root system response of banana and plantain cultivars...
TRANSCRIPT
Root system response of banana and plantain cultivars to an agroforestal tree shade gradient
in the central highlands of Costa Rica
(Reaktion von Bananen- und Kochbananen-Wurzelsystemenauf einen agroforstwirtschaftlichen Schatten-Gradienten
im Zentralen Hochland Costa Ricas)
Diplomarbeit
für die
Diplomprüfung
zur
Erlangung des Grades: Diplom-Agraringenieurin (Dipl.-Ing.agr.)
der
Landwirtschaftlichen Fakultät
der
Rheinischen Friedrich-Wilhelms-Universität
zu
Bonn
Vorgelegt am XX. Oktober 2011
von cand.agr. Charlotte Dreiseidler
1. Prüfer PD Dr. Jürgen Burkhardt
2. Prüfer Dr. Beate Pfistner
Erklärung
Ich versichere, dass ich diese Arbeit selbstständig verfasst und meinen Anteil
kenntlich gemacht habe, und dass ich keine anderen als die angegebenen
Quellen und Hilfsmittel benutzt sowie Zitate kenntlich gemacht habe.
Bonn, den XX.10.2011
Charlotte Dreiseidler
2
Acknowledgements
I would like to thank the GIZ (Gesellschaft für Internationale Zusammenarbeit
GmbH) and Bioversity International for allowing me to experience a great time; by
their sponsorship and facilitation of getting known to science.
I would like to express my gratitude to my supervisors, PD Dr. Jürgen Burkhardt
and Dr. Charles Staver, and my colleagues Dr. Oscar Bustamante and Dr. Pablo
Siles; for your ideas, patience and active support. I want to thankfully mention the
Bioversity research team at CATIE, and Erwid Valdivia, who designed and
maintained the experimental plots.
At the end I would like to thank all those, that made the time in CATIE, in
Bioversity office and here at home a fun and feeling-well-kept time. Thank you for
being with us.
3
Summary
In an organic coffee farm in Turrialba, located in the Central Highlands of Costa Rica, four cultivars of Musa were grown in four plots of varying levels of shade (minimal (8%), 25%, 50% and 75%
shade) by the leguminous Poró (Erythrina poeppigiana). The banana plants were sampled at ~6 month age by two soil coring methods. The roots of Musa and the ‘other‘ species, i.e. Poró and
coffee dwarf variety ‘Caturra‘ were washed from soil, separated, scanned and weighed for roots >1mm diameter. Each three plants per shade level from AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘),
AAB ‘Curraré‘ and ABB ‘Pelipita‘ were sampled by 4 large samples (monoliths with 18000 cm3 soil volume) at 40 cm distance from the plant. The twelve plants of AAA ‘Gros Michel‘ were before
additionally sampled by 20 small samples (auger of 567,5 cm3 volume) at 40, 80 and 120 cm distance from the plant and in two soil layers, 0-10 cm and 10-20 cm depth. A comparison of both
methods revealed, that large samples are advantageous in customisation of their sampling tools, in low standard errors (% of mean) and balancing the spatially heterogeneous Musa root system. And
small samples are advantageous in positioning of sample locations in the densely planted system, and the soil volume is more convenient in processing. The sampling intensities of both methods
were well chosen, leading to <10 %SE/M. We suggest 80-100 auger samples or 16-20 monoliths per studied group (i.e. shade level, cultivar), and to create a middle-sized squarely formed sample.
The Musa root contents in samples of both methods were analysed. Shade significantly influenced the Musa roots in monoliths, which sharply decline under 75% shade. AAB ‘Curraré‘ and ABB
‘Pelipita‘ have more and denser roots. The specific root length increases under 75% shade in both methods, i.e. Musa roots supposedly are thinner. Shade insignificantly influences AAA ‘Gros
Michel‘ roots in auger samples, which equally decline under 75% shade. The banana roots in the auger samples significantly decrease with depth, insignificantly decrease in distance (horizontal),
and both declines are stronger under 75% shade. In both methods, Musa roots do not alternate in the coffee-row proximity. The ‘other‘ roots in samples of both methods always form the major share.
They do not develop contrarily in shade levels, i.e. only poorly increase under 75% shade. In the auger samples, a spatial complementarity is detectable, and near coffee-rows the ‘other‘ roots are
denser and more than in inter-rows. The Musa and ‘other‘ root share are uncorrelated in samples of both methods (correlation coefficient <0,3). The Musa root contents in samples are weakly
correlated to light parameters (CC > 0,3), uncorrelated to soil moisture (CC < 0,3) and moderately correlated to shoot traits or biomass (CC < 0,6). At the end, we estimated the total root system of
AAA ‘Gros Michel‘ out of the auger method. We calculated the share of one monolith of the total root system, and transferred this percentage to the other three Musa cultivars. Shoot-root ratios
were calculated for total dry shoot to root biomass. The SRR decrease from minimal to 25% shade, by an increase of root biomass. The SRR then increase under higher natural shading. As both the
shoot and root biomass declines, the root biomass must be declined stronger. Therefor, we see the light deficiency as the major impact upon Musa root formation. The relations of roots to the shoot
development is the essential one, which determines the root decline in 75% shade, stimulated by the low light availability. The root system is probably discriminated in favour of forming more leaf
area in the bananas, to capture the reduced available light still penetrating the Poró canopy.
4
Zusammenfassung
Auf einer Farm für organischen Kaffee, im Zentralen Hochland Costa Ricas nahe Turrialba, wurden vier Bananen-Sorten unter wechselnden Schattenniveaus (minimal (8%), 25%, 50%, 75%) durch den N2-fixierenden ,Poró‘ (Erythrina poeppigiana) angebaut. Die Bananen wurden im Alter von 6 Monaten durch zwei Arten Bodenproben beprobt. Die Wurzeln der Musa-Sorten und die anderer Pflanzen, d.h. ‘Poró‘ und der Zwerg-Kaffeesorte ,Caturra‘, wurden durch Waschen von der Erde gelöst, sortiert, gescannt und gewogen (nur Wurzeln >1mm Durchmesser). Je drei Bananen pro Schattenniveau der Sorten AAA ,Gros Michel‘, AAA ,Red‘ (syn. ,Morado‘), AAB ,Curraré‘ und ABB ,Pelipita‘ wurden ausgewählt und mit je 4 großen Proben (eng. ,monoliths‘ á 18000 cm3 Volumen) in 40cm Entfernung von den Pflanzen beprobt. Die zwölf Pflanzen von AAA ,Gros Michel‘ wurden zuvor mit je 20 kleinen Proben (Bohrkerne, eng. ‘auger samples‘ á 567,5 cm3 Volumen) in 40, 80 und 120cm Entfernung und in zwei Bodentiefen, 0-10cm und 10-20cm, ebenfalls beprobt. Der Vergleich beider Methoden ergab, dass die großen Proben in der Anpassungsfähigkeit ihrer Entnahmewerkzeuge, in niedrigen Standardfehlern (% des Mittelwerts) und im Ausgleich der räumlich heterogenen Wurzelsysteme der Bananen vorteilhaft sind. Die kleinen Proben hingegen sind im einfachen Positionieren der Entnahmeorte innerhalb des dicht gepflanzten Systems und des geringen zu verarbeitenden Volumens von Vorteil. Die Intensität der Beprobung war in beiden Fällen gut gewählt, da sie die %SE/M auf <10 reduzierten. Wir empfehlen 80-100 Bohrkerne oder 16-20 ,monoliths‘ je zu testender Gruppe (d.h. Schattenniveau, Sorte), und die Entwicklung einer Probenart von mittlerer Größe und quadratischer Form. Die Bananen-Wurzelgehalte in Proben beider Methoden wurden analysiert. Das Schattenniveau beeinflusst signifikant die Musa-Wurzelgehalte der Proben und zeigt deren starken Rückgang in 75% Schatten. AAB ,Curraré‘ und ABB ,Pelipita‘ haben vermehrte und dichtere Wurzeln. Die spezifische Wurzellänge ist in Proben beider Methoden unter 75% Schatten größer, d.h. vermutlich sind die Bananenwurzeln dünner. Das Schattenniveau beeinflusst die Musa-Wurzelgehalte in den Bohrkernen nicht signifikant, dennoch sind diese in 75% Schatten reduziert. Die Bananen-Wurzelgehalte gehen signifikant mit der Bodentiefe und nicht signifikant in der zunehmenden Distanz von der Pflanze zurück, und dies verstärkt in 75% Schatten. In Proben beider Methoden werden die Bananenwurzeln nicht durch die Nähe der Kaffeereihe beeinflusst. Die ,anderen‘ Wurzeln bilden immer den größeren Anteil in den Proben beider Methoden. Diese entwickeln sich nicht gegensätzlich zu Musa-Wurzeln in den Schattenniveaus, d.h. sind nur marginal vermehrt in 75% Schatten. In der Bohrkern-Methode ist eine räumliche Komplementarität erkennbar, und die Proben in Nähe der Kaffeereihen weisen erhöhte Wurzelgehalte verglichen mit den Zwischenreihen auf. Die Musa- und ,andere‘ Wurzelgehalte in den Proben sind zueinander unkorreliert (Korrelationskoeffizienten <0,3). Die Musa-Wurzelgehalte sind schwach korreliert zu Licht-Parametern (CC > 0,3), unkorreliert zur Bodenfeuchtigkeit (CC < 0,3) und moderat korreliert zu oberirdischen Bananen-Parametern oder -Biomasse (CC < 0,6). Zu guter Letzt schätzten wir das gesamte Bananen-Wurzelsystem der AAA ,Gros Michel‘ Pflanzen durch die Bohrkern-Methode. Dann berechneten wir den Anteil eines ,monoliths‘ am gesamten Wurzelsystem, und übertrugen diesen Prozentanteil auf die drei anderen Musa-Sorten. Wir berechneten die ,shoot-root ratios‘ (ober- zu unterirdischer Biomasse). Diese sinken von minimalem zu 25% Schatten durch einen Anstieg an Wurzelbiomasse in allen Sorten. Danach steigen die SRR unter hohen Schattenniveaus an. Da sowohl ober- wie unter-irdische Biomasse abnimmt, muss die Wurzelbiomasse stärker reduziert werden. Insgesamt gehen wir davon aus, dass der Lichtmangel der Haupteinfluss auf die Bananenwurzeln ist. Das Verhältnis der Wurzeln zur oberirdischen Biomasse ist das Entscheidende, das den Wurzelrückgang unter 75% Schatten zu verantworten hat, folgend auf eine Stimulation durch Lichtmangel. Das Wurzel-system wird womöglich zugunsten der Blattfläche der Bananen diskriminiert, um so viel wie eben möglich des reduzierten Lichts, das durch das Poró-Blätterdach dringt, aufzufangen.
5
Content
1. Introduction ..........71.1 Background of a Latin American project ..........81.2 Musa spp.: bananas and plantains .........111.3 The growing system of bananas, coffee and trees .........201.4 Root sampling methods .........31
2. Hypotheses .........373. Experimental sites .........38
3.1 Geography and climate .........383.2 Experimental plots .........403.3 Soils .........44
4. Materials and methods .........474.1 Data collection .........474.2 Data analysis .........52
5. Comparison of sampling techniques .........555.1 Comparison of methods .........55
5.1.1 Field work & project embedment .........565.1.2 Lab work & results .........585.1.3 Improvement .........63
5.2 Statistical comparison .........655.2.1 Preciseness .........665.2.2 Sampling intensity .........69
5.3 Conclusion .........756. Root formation .........76
6.1 Musa root biomass .........776.1.1 Allocation .........776.1.2 Spatial distribution .........83
6.2 Tree and coffee root biomass .........906.2.1 Formation .........906.2.2 Correlations to Musa roots .........96
6.3 Estimation of total Musa root system .........986.4 Conclusion .......106
7. Below- and above-ground relations .......108 7.1 Relations below- and aboveground .......108 7.1.1 Environmental parameters .......108 7.1.2 Plant parameters .......112 7.2 Shoot-root ratios .......115
7.3 Conclusion .......1218. Conclusions .......122 8.1 Farming improvement .......124 8.2. Perspectives .......1269. Annex .......128
A. List of all Tables .......128B. List of all Figures .......129C. Abbreviations .......130D.+E. Post-Hoc tests .......131F. Shoot biomass of Musa .......134
10. References .......135
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1. Introduction
In a rather short period of five and a half months, this study was carried out at
CATIE (‘Centro Agronómico Tropical de Investigación y Enseñanza‘), a world-
renowned agroforestry research centre in Costa Rica, for the INIBAP
(‘International Network for the Improvement of Banana and Plantain‘) department
of Bioversity International. As the particular study was part of a larger project
context, the very capable situation enabled me to do far more than an individual
root testing would have produced during five months. Studying the roots of
bananas and plantains is a challenging and interesting activity, and our research
team gained some very promising results.
Combining several species of agricultural crops on one unit of arable land was
lately a focus of Bioversity International in Latin America. Growth resources, which
are water, sun light and nutrients, may be utilised more effectively by several crops
(Nair, 1993), and a couple of beneficial effects in both an environmental context
and secured economic returns for producers may support a successful farming.
Roots of Musa cultivars were addressed in diverse aspects by researchers, who
summarised a great deal of knowledge in Turner and Rosales (2005). Out of the
roots‘ point of view, the competitive interactions in the mixed-species system and
the effects of natural shading should be tested in this study. ‘Competition‘
impacting Musa would be defined as a yield depression and an economical failure
(Schroth, 1999).
The banana root system may be defined as “a population of roots of different types
and age that evolve dynamically according to root formation and root senescence“,
by Draye (2002). Our purpose was to study the root architecture and shoot
development of 6 month old, shaded Musa plants (Objective A). Additionally, we
involved a methodological aspect and carefully observed soil coring methods we
used in our field grown bananas and plantains (Objective B).
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1.1 Background of a Latin American project
Over three years, 2009 to 2011, the project ‘Improving small farm production and
marketing of bananas under trees: Resource partitioning, living soils, cultivar
choice and marketing strategies‘ is conducted by Bioversity International, member
of CGIAR. Bioversity International devoted itself to worldwide, development
orientated agricultural research - to the “conservation and use of agricultural
biodiversity - to improve peoples lives“. The banana department of Bioversity
International, INIBAP, takes over responsibility in conserving banana and plantain
biodiversity and maintaining their productivity, since they form a major staple food
crop in tropical parts of the world. Four Latin American countries are subject to
several individual studies, Peru, Honduras, Nicaragua and Costa Rica. Funded by
the German International Corporation, GIZ, its primary intention is to improve the
living conditions of smallholder farmers in Latin America, by improving commonly
planted banana and plantain cultivars, in a multi-species growing system, to
increase the farmers‘ returns of income and production. German universities, like
the University of Bonn, cooperate with Bioversity as well as about twenty different
national research organisations. The studies focussed in both agricultural and
socio-economic terms upon growing systems combining banana and coffee as
valuable products, in farm-based experiments including interrogations and
analysis (e.g. Dold, 2010), and several rather stationary experiments like this one.
Costa Rica produced in 2008 sugar cane, bananas and pineapples in topmost
positions; still, bananas and pineapples share the position of highest values ($)
and export quantity1. Costa Rica (in brackets: World) produced in 2008 2.127.0002
tonnes (93.813.033 tonnes) of bananas and 85.176 tonnes (34.911.224 tonnes) of
plantains, whereof 96,5%3 (19,17%) of bananas and 21,4% (1,38%) of plantains
were exported. Therefor, Costa Rica as one of the top Musa spp. producing
countries in the world exports an unusual high proportion of its production. Still,
8
1 All data by http://faostat.fao.org; date of access: 26 June 2011
2 Most data include estimations or semi-official data, as marked by FAO.
3 Values calculated by using FAO production/ trade data, calculated by me
domestic supply is a major sink for Musa harvests. In 2009, Costa Rica banana
production increased, whilst Costa Rica plantain and World production for the two
of it decreased. Bioversity International states that less than 15% of Worlds
banana production is exported, the remaining part locally consumed. At some
places, they mention, people eat close to 1kg of bananas per day4 . According to
the FAO, Costa Rican people consumed 0,43 kg/capita/year of bananas and 8,67
kg/capita/year of plantains in 20075.
The world development report (‘WDR‘) 2008 ‘Agriculture for Development‘ (The
World Bank, 2007), considers Latin America and the Caribbean as being mostly
‘urbanised countries‘6. ‘Paradox‘ though it may be, the large agribusiness sectors
of those countries did considerably well in terms of productivity, but the rural
people were not equally well affected. The WDR2008 estimates, that agriculture
has 2,7 times the potential to reduce poverty in Latin America than non-agricultural
growth has. Costa Rica had 25,5% rural poverty and 19,2% urban poverty in 1992
(The World Bank, 2007). Honduras, Nicaragua and Peru, who are the
accompanying project countries, had a share of approx. > 70% rural poverty (The
World Bank, 2007; in the years Honduras 1998/99, Nicaragua 1993, Peru 2001).
Agribusiness sector had 7% of GDP in Costa Rica in 20097, with a major share of
the service sector accounting for 66% GDP in 20098. The development incentive
stated is “linking smallholders to new food markets and providing good jobs“ (The
World Bank, 2007). Policy objectives suggested, reduced to agricultural objectives
9
4 INIBAP Website, http://bananas.bioversityinternational.org/en/; date of access: 27 June 2011. Both information supposedly account for Musa spp. generally.
5 All data by http://faostat.fao.org; date of access: 27 June 2011
6 Therefor requiring different attention than ʻagriculture-basedʻ or ʻtransformingʻ countries. ʻUrbanised countriesʻ are roughly characterised with the agribusiness contributing approx. 5% of national growth 1993 to 2005 and the sector of agribusiness and food industry share about one third of the Gross Domestic Product (ʻGDPʻ). Poverty is to be found mostly urban, though rural poverty may be 45%. (The World Bank, 2007)
7 World Development Indicator by The World Bank, http://data.worldbank.org/indicator. Date of access: 01 August 2011.
8 Honduras: 12% (Agriculture of GDP), 60% (Service of GDP); Nicaragua 19%/ 51%; Peru 7%/ 59% (all 2009). Data: World Development Indicator by The World Bank, http://data.worldbank.org/indicator. Date of access: 01 August 2011.
as they are of our interest, are the participation of smallholder farmers as
competitive suppliers in “dynamic, domestic food markets“ and the productivity
increase of subsistence farmers, combined with valuing environmental services
and further social assistance. The former may demand training, producer
organisations and innovation through science and technology; the latter ‘resilient‘
farming systems. Such could “improve livelihood in subsistence agriculture“ -
though little potential for economic growth, the product diversification, stabilisation
of food supply and economic output till long-term sustainability, and contribution to
worker and family health and environment by less pesticide pollution (amongst
others) could do their share (The World Bank, 2007).
The large ‘environmental footprint‘ of agriculture affects both contemporary and
future peoples‘ health, food and environmental sustainability (The World Bank,
2007). Mismanaged irrigation water, biochemical pollution, pesticide poisoning and
food production stability are some aspects. Costa Rica had an amount of 225,3
[hundred grams pesticides per hectare of arable and permanent cropland] used in
2000-2002 (The World Bank, 2007). Though in WDR2008 the pesticide amount
spent was unavailable for most countries, Costa Rica is first worldwide followed by
Colombia (166,7 [hundred grams pesticides per hectare]). Exemplary,
monocultural, intensively grown bananas on export plantations are very
demanding, in both fertiliser and especially pesticide use. Plantations are located
in the lower and hence warmer regions of Costa Rica. Though the studies are
presently primarily directed to the contemporary farmers‘ benefits, the long-term
purpose aims at developing systems and methods, which one day may have a
larger share of the export markets as well. Those improved systems may be
rather suitable to environmental and sustainable issues and enable a production,
that considers future generations and an intact, powerful surrounding.
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1.2 Musa spp.: bananas and plantains
Musa spp.
Banana, plantain and cooking bananas are perennial, gigantic herbs of the genus
Musa, mostly section Eumusa with chromosomes (2n = 22). Most cultivated
varieties nowadays are triploid hybridizations of two species of that section, Musa
acuminata (‘A gene‘) and Musa balbisiana (‘B gene‘). Although diploid and
tetraploid varieties exist just as well, triploid cultivars are widely planted. Though
botanically not justified (Carr, 2009), the triploid cultivars are commonly referred to
(amongst others) as AAA dessert bananas, AAB plantains and ABB cooking
bananas (Draye, 2002). The genes are sometimes determined as source to
effects, as better (seasonal) drought and disease tolerance of Musa balbisiana
with the B gene (Daniells et al., 2001; Carr, 2009). Sensitive to environmental
changes, bananas generally like warmth, humidity, light, avoid competition and
poorly drained soils, and species differ in their adaptability (Turner et al., 2007).
The true stem, a rhizome, is located below-ground and called ‘corm‘. Shaped like
a bowl it has approx. 35cm height and 30cm horizontal length (Carr, 2009; Draye,
2002). Leaf primordia encircle the shoot apex in a rosette and form a ‘pseudo-
stem‘, which is pierced by the inflorescence during shooting (Carr, 2009; Draye,
2002). The vegetative phase of planting to flowering is the main phase of root
growth (Carr, 2009; Draye, 2002), therefor most roots are to be found at begin of
flowering (Blomme, 2000a). So typical for monocotyledons, the primary roots are
root axes, called ‘cord roots‘, and emerge in bundles of 3-4 at the upper part of the
corm from a cambium-like layer (the ‘Mangin zone‘, Draye, 2002; Blomme, 2000a).
In strict orders, primary, secondary and (seldom) tertiary laterals emerge, and are
thinner and shorter, respectively (Araya, 2005), just like root hairs; though Draye
(2002) and Swennen et al. (1988) mentions them to cover the root axes; Blomme
(2000a) says they are sub-ordered to the last laterals present; Belalcázar et al.
(2005) say they grow at the active ‘end‘ of each order. Those laterals and root
hairs are mainly responsible for water and nutrient uptake, i.e. hydrological
conductance, and form the major interface to the soil (Turner et al., 2007).
Cultivated species are chosen for their edible fruits, which are thus parthenocarpic
11
and hence have female infertility (i.e. non-seeded; Daniells et al., 2001). Given
that, mother plants need to reproduce vegetatively by lateral shoots, called
‘suckers‘, or clones (Carr, 2009); the former are formed in remarkable sizes and
numbers during the vegetative phase of the mother plant, i.e. in our case 0-6
suckers after approx. 6 months growth, and they emerge from buds at the rhizome
(Carr, 2009; Turner et al., 2007).
In the study at hand we observed the widely accessed AAA ‘Gros Michel‘ and the
AAA ‘Red‘, synonym ‘Morado‘; the cooking banana ABB ‘Pelipita‘ and the plantain
AAB ‘Curraré‘. Both dessert bananas are to become pseudostems ≥ 3m tall and
robust; Pelipita‘s pseudostem may be 2,1 - 2,9 m and ‘normal‘ (Daniells et al.,
2001)9. Additionally, the catalogue says suckers grow vertically, close to the
mother plant to three quarter of its height for all three species, with Pelipita having
6 or more. Genotypic differences in root formation and phenotypic responses are
maybe slightly higher for controlled (‘in vitro‘) experiments, than field (‘in vivo‘)
ones (Draye, 2002), and high variabilities of root development in fields obscure
genotypic differences (Blomme, 2000a). The level of ploidy seems to rise the
‘magnitude‘ of shoot and root plant parameters (Blomme, 2000a). In the very same
field trial, the author found genotypic variability due to genome groups (AAA, AAB,
ABB) for root characteristics, with plantain and cooking bananas having larger root
systems than dessert bananas. But Swennen (1984) found bananas to have two
times the length and density of plantain (AAB) root systems. Increased competition
leads commonly to a higher variability from plant to plant in root traits (Carr, 2009).
Consequentially, “the [banana] root system is strongly modified by the soil
environment“ (Turner et al., 2007) becomes reasonable. The banana roots form a
dense and shallow ‘mat‘, even compared to other fruit crops shallow (Turner et al.,
2007), in which axes, laterals and hairs are rather horizontally distributed than
vertically (Blomme, 2000a; Draye, 2002), a “radial horizontal type“ (Belalcázar et
al., 2005). Thus the ‘effective rooting depth‘ is limited to 30 - 40 cm from the
ground surface, in which water uptake etc. may take place (Carr, 2009). Turner et
12
9 Unfortunately, no root characteristics are given in there, and plantain Curraré was not found.
al. (2007) state that the shallowness may be believed to be of edaphic induced
origin, rather than a quality which is inherent to the crop itself; as the authors
report banana roots that were found in 1,5 - 1,8 m in deep soils. Problematic in soil
volume restricted root systems are rather mechanical issues, for the root mat has
to provide enough anchorage for the tall pseudostem, the broad leave canopy and
the considerable bunch mass, i.e. 20-50 kg likely (Draye, 2002); as that they are of
growth resource availability restraints (see below; Blomme, 2000a). The banana
root system traits may be broadly summarised like this: a rhizome may have
200-400 root axes in its vegetative cycle, which elongate 2-3 to 5 m from the
pseudostem, and thus may reach to 230 m in total length; their growth rate is said
to be 60cm month-1 or 2 - 3,5 cm day-1, and they leave the rhizome at 30° angle,
though not reach to the by then calculated anticipated depth; hence emerge flat,
turn downwards with age (i.e. ‘negative geotropic growth‘); and most root system
is to be found within the first 60cm from the pseudostem, and laterals emerge from
primary roots most proximal to the rhizome; or 90% within 1m from the plant and
70% in 20 - 40 cm depth; and finally, the dry biomass of a banana or plantain mat
may be 1,1 - 4,9 kg at flowering, due to variety measured (Swennen, 1984; et al.,
1988; Blomme, 2000a; et al., 2000b; Draye, 2002; et al., 2005; Turner et al.,
2007). In AAA ‘Grand Naine‘, Araya (2005) found > 80-95% root fresh weight in the
first 45 cm; and defined the stratification of ‘Grand Naine‘ and ‘Valery‘ as 40% in
topmost 15 cm, >65% root fresh weight in topmost 30 cm, and finally 88% within
the top 60 cm.
The phenotypic development of roots (root traits) in the field, as branching,
elongation or diameters, are “a function of genotype, plant status, root age and
rhizospheric conditions“ (Draye, 2002). Schroth (1999) states that “genetic factors
interact with environmental factors“ (i.e. ‘compensatory root growth‘), thus planning
growth systems must augment the most adequate combination. That plasticity of
growth, so Blomme (2000a), is determined by amongst others planting material,
biophysical factors like climate, pest and disease pressure, soil properties; the
author expects edaphic factors (like soil moisture, anoxia, nutrient contents, bulk
density, soil texture and structure, land preparation, previous crops, ...) to be more
important than shoot characteristics; e.g. light availability, in terms of carbohydrate
13
assimilation to enable root growth. Gauggel et al. (2005) lists many root system
deterioration cases; prominent effects and symptoms are injuries, poor root
development, shorter or rotten roots, respective of the cause. Araya (2005) found
optimal soil for Musa growth to be “slightly acidic, deep, rich and well drained“, and
named clayey loam or any loam soils. Vaquero (2005) named soil texture,
compaction and drainage as major influences; aeration and low mechanical
resistance are demanded for normal growth, whereas impermeable layers, high
clay contents and waterlogged areas should be avoided. The author found > 15%
coarse soil particles and > 60% clay both to reduce Musa optimal root growth, (i.e.
root length density); in the first case, caused by the low water retention capacity,
and in the second by the low permeability. Thus, the author considers Musa root
growth best in fine sandy loam or clay loam; as Musa form more extensive and
deeper root systems in soils, of finer texture, good structure and porosity.
Bananas still produce more sufficient yields in acidic soils than other crops, in a
wide range of pH 4,5 - 8,5 (Draye, 2002). The author finds Aluminium toxicity to be
accompanied by reduced diameter of laterals, thus a reduced main surface of
growth resource uptake. Soil temperatures are positively correlated to root growth
(Carr, 2009; Blomme, 2000a). Mulch applications increased root growth and
suckering, but causes superficial root mats too (Swennen, 1984; Araya, 2005);
Musa roots are orientated towards fertile and high concentrated organic matter
areas of the soil (Belalcázar et al., 2005). Blomme (2000a) found field grown
bananas to have relatively much roots in low nutrient conditions, possibly to exploit
more soil to support the shoot. Bananas prefer less mobile NO4- to NH3+ for
nitrogen uptake; and demand constant amounts of potassium, as Musa plants hold
high water amounts per soil area; the two uptake mechanisms require energy and
release protons into the rhizosphere, thus attribute to soil acidity (Turner et al.,
2007). Waterlogging, to which bananas are sensitive, causes shallower root
systems, growth restrictions and thus plant size and yield reductions (Draye,
2002). The author reported approx. 68% of mycorrhiza invasion in Musa roots,
which has positive shoot effects, acts useful as P fertilisation and is advantageous
for smaller root systems, and even may reduce the root number.
14
Mechanical impedance may severely restrict the banana root system in size and
distribution, as active root tips are soft and “sensitive to penetration
resistance“ (Draye, 2002; et al., 2005). Vertical exploitation of Musa roots is
reduced by soil compaction, high clay contents, saturated or impermeable layers
(Blomme, 2000a). If exploitation is limited, chemical effects are induced, such as
root uptake capacity; those chemical and mechanical effects are sometimes
difficult to be separated (Draye, 2002). Root axes elongation is more affected than
the laterals emergence (similar to be found for low pH conditions), and root axes
may become thicker, what is related to reduced uptake capacity and hydrological
conductance (Draye, 2002; Araya, 2005). Belalcázar et al. (2005) found heavy
texture to cause shorter and thicker (0,4 - 1 cm), lighter texture longer and thinner
(0,6 - 1,3 cm) Musa roots. By reviewing studies, Draye (2002) states that restricted
Musa root system size does not necessarily limit the uptake, as the additional root
growth is more important in influencing absorption. Equally, Blomme (2000a)
mentions that a reduced root system size may just as well supply a vigorous Musa
plant, if the growth resources (i.e. primarily nutrients and water) are sufficiently
provided in the banana rooting zone.
The positioning of active, functional roots is at least as important as the elongation
of structural roots. The preferred layers and mechanisms of uptake vary amongst
nutrients. Buresh et al. (2004) and Schroth (1999) both cite an IAEA study of 1975,
in which uptake patterns of radioactive phosphorus were tested around tree crops
by soil injections. The highest uptake was close to the soil surface (30 cm), except
for Kenyan coffee (45-75 cm depth). In lateral distribution, coffee and Musa
paradisiaca had those uptake at 30-100 cm distance from the trunk; although
extensive root growth would have been possible. Schroth (1999) anticipates a
higher competitiveness in that parts, and Draye (2002) generally concludes that
increased root growth or uptake may take place in nutrient-rich areas, by root
plasticity, thus conclusions of such experiments may be limited. The author
reviewed other studies to show P uptake in the topmost 15 cm layer, and 60 cm
from the rhizome; for water, topmost 10 cm layer (40%) and 30 cm (80% of total
uptake).
15
Shading and Yield
“Obviously, an improved root system will result in better anchorage, faster growth
and higher yield“ (Blomme, 2000a). Negatively affected rhizomes or roots fail to
support the shoot components with sufficient growth resources, anchorage and
thus yield declines are likely (Blomme, 2000a). Infestations with nematodes
(Fernández et al., 2005: Radopholus similis, Meloidogyne incognita, Pratylenchus
coffeae, Helicotylenchus multicinctus) or banana weevil (Cosmopolites sordidus)
of nematodes, banana weevil [or Fusarium wilt] are widely observed and the
according yield declines too (Swennen et al., 1988). Infestations are stronger in
high root density areas (Draye, 2002). Plantains are relatively sensitive, in poor
yielding from the 2nd harvest cycle on; by poor suckering, that was related to
diseases, organic matter demand etc. (Swennen et al., 1988.). Blomme (2000a)
found roots reduced by nematodes still able to support a relatively vigorous shoot.
Costs to maintain root length elongations may rise in stressful conditions, thus a
greater share of photosynthetic energy will be needed (Draye, 2002). Given all
that, Musa yield is determined by root conditions or restraints, that are of genetic,
environmental, edaphic (physical, chemical) or biological nature (Turner, 2005;
Swennen et al., 1998; Gauggel et al., 2005).
Sun light, and consequentially photosynthesis to assimilate carbohydrates, is the
‘engine‘ of any plant growth. Carbohydrates form major construction parts of
plants, and roots depend entirely on their provisioning by the shoot; reduced
assimilation will affect root growth and functioning (Turner et al., 2007). The author
adds, that Musa light response curves vary. Musa plants photosynthate by C3
pathway (Carr, 2009), which inherits a lower water-use efficiency or temperature
optima than C4 or CAM-plants have (Nair, 1993). The author describes, that
transpiration is higher and shade adaption better for C3 plants, as they still
assimilate carbon at low irradiance levels; C4 plants are better adapted to full sun
radiation. The root pressure is high in bananas, keeping the leaves hydrated
(Turner et al., 2007). Stomata are to be found adaxial (upper) and abaxial (lower -
up to four times denser stomata) on leaves, of which adaxial stomata are wider
open on sunlit leaves, and the other way around on shaded leaves (Carr, 2009).
The author indicates that shaded leaves are less sensitive to soil water changes.
16
Fig. 0 Banana yield response to shade, schematised by Turner et al. (2007, p. 466). Line A = anticipated yield
response of banana to light reduction, “based on the efficiency of growth of well shaded plants“; Line B and C
= increased radiation causes no yield response, as other growth factors than light are limiting yield.
Robinson and Nel (1989) found sunlit and mutually shaded leaves of AAA
‘Williams‘ to have 20,9 ± 1,5 µmol CO2 m-2 s-1 (sunlit) net CO2 uptake, and 6,8 ±
1,0 µmol CO2 m-2 s-1 (shaded), and stomatal conductance was reduced analogue.
The photosynthetic active radiation (PAR) received was reduced by 5% and
accordingly, the net carbon dioxide uptake decline to 32% (shaded of sunlit leaf).
Any Musa plant grown under shade (‘protective cover‘) reacts to the newly given
radiation profile (Turner et al., 2007). The author referred to an own former
publication, saying, that Musa responses may be distinguished for moderate (light)
or hight (deep) shade levels (Fig. 0). In deep shading (intensity not further
specified), irradiance reduction restricts Musa root growth and yield increases
proportional to the received sunlight. In moderate shading, other factors become
limiting instead. The author suggests, that growing bananas understory could save
water, as long as “the root zones of the bananas and overstory did not overlap to a
large extent“.
Schaffer et al. (1996) conducted in vitro experiments of AAA ‘Gros Michel‘ grown in
root chambers and glasshouses. Bananas in 200 l chambers were
photosynthetically more efficient; and had higher leaf area and plant dry weight
than those in 20 l (restricted root growth), at ‘normal‘ CO2-concentrations of 350
µmol CO2 mol-1, whereas in 1000 µmol CO2 mol-1 no chamber effect upon dry
17
Fig. 1 Net CO2 assimilation (A) of banana, Musa AAA ‘Gros Michel‘, to varying CO2 concentrations in the leaf
cuvette (Ca) for plants grown in large (200 l) and small (20 l) root chambers. Regression lines are in large
chambers A = 102,65 ([-85,13 + Ca] / [796,95 + Ca]) and r2 = 0,95; and in small chambers A = 87,81 ([-85,96 +
Ca] / [863,08 + Ca]) and r2 = 0,92. Data were pooled from 350 and 1000 µmol CO2 mol-1 treatments, as no
significant interaction between ambient carbon dioxide concentration and root chamber size occurred (P >
0,05). Adapted and shortened from Schaffer et al. (1996; p. 688).
matter was observed. Large chamber bananas had higher net CO2 assimilation
rates (Fig. 1). The build-up of starch in leaves was suggested, if the strength of the
sink, i.e. roots, is reduced; but the author say that it could not be confirmed and
the rhizome may act as an additional partial starch sink. Turner et al. (2007)
developed those data and subdued them to ‘the curve fitting procedure‘ given by
Sharkey and colleagues10, and found an approx. 25% reduction in plant growth by
root restriction, to 1686 g (20 l pot) of 2272 g (200 l pot) plant dry weight.
Photosynthetic biochemistry was changed insofar, that the maximum carboxylation
rate, which is allowed by RubisCo, was reduced by 46% and the day respiration
rate increased by 44% (in small 20 l pots).
Lecompte et al. (2005) grew AAA ‘Grande Naine‘ in field (FE) and glass house
(GE) experiments, with a 5 times lower radiant flux density in the latter. The shoot
biomass was similar, but the leaf area increased more rapidly in GE, and specific
leaf area was higher. GE-bananas also had less root axes, significantly lower
diameters of secondary roots, significantly lower branching density on root axes
and a lower primary root growth. As the author reviewed typical low-light-
18
10 Sharkey and colleagues (published 2007) are cited by Turner et al. (2007). See References in: Turner et al. (2007).
availability-responses to be: decreasing shoot-root ratios, lower root branching
density and reduced diameters, and noted that other environmental influences like
temperatures and water were similar for both GE and FE, he concluded that the
root reduction as a consequence of less radiation, maybe in terms of less
assimilates provided for the root system, seems plausible. Additional, the roots of
‘higher order‘ (i.e. 2nd or 3rd laterals) were stronger affected (diameter reduction),
thus the growth resource uptake must be reduced in return, as they form the major
surface contact (see Chapter 1.3; Turner et al., 2007).
In planting density experiments, Robinson and Nel (1988) found the pseudostem
height and stem circumference to increase with plantation age, e.g. 2,6 to 3,95 m
height and 0,79 to 1,13 m diameter, from the plant cycle to the 4th ratoon cycle in
AAA ‘Williams‘. Their annual yield potential was determined by changing (harvest)
cycle intervals. Sucker emergence to harvest intervals increased with planting
density and age, thus indicating competition, i.e. 15,5 months duration in 1st ratoon
crop and 1000 plants ha-1; to 30,9 months in 2nd ratoon crop and 2222 plants ha-1.
Additionally, the authors remark stability in a morphological and phenological
sense to determine optimal planting densities are given only after four crop cycles,
thus indicating the interdependence of plantation age and density.
In a 16-year long study, 1987 - 2002, Serrano (2005) compared the experienced
yield losses to the content of functional root losses in Costa Rican commercial
plantations. The author found evidence of positive relations, exemplary shown for
four regions. Given is the loss of boxes11 ha-1 year-1 per loss of 10 g functional
Musa roots: in Sarapiquí 60, in Pococí 140, in Siquirres 55, in Talamanca 99
[boxes ha-1 year-1]. As causes the author suspected (a.o.) nematodes, anoxia, un-
drained soils, acidity, thus: dead roots, less healthier roots, less productivity.
Blomme (2000a) pointedly admits: maximal photosynthesis rates are the desirable
condition to be achieved, instead of maximal root proliferation, in an economic
sufficient plant growth.
19
11 Traditional banana harvest: 1 box = 18,14 kg fruit.
1.3 The growing system of bananas, coffee, trees
Root competition
Bananas and plantains (Musa spp.), combined with Coffea arabica, are densely
and spatially mixed intercropped with Erythrina poeppigiana. Dense, simultaneous
mixed-species agroecosystems have a most large tree-crop interface (‘TCI‘;
Young, 1997), at which competition rather than synergetic improvement is likely to
occur (Rao et al., 1998); competition and facilitation are system-inherent
characteristics (Schroth, 1999). In multi-strata systems, above-ground competition
is mainly varying canopies competing for sun light (radiation), thus photosynthesis;
below-ground competition is merely competition for water and nutrients, by
presence of roots (Khanna, 1998). The ‘key characteristic‘, by which root
competition is measured, is “root length density (RLD) of each plant component in
different layers of soil“ (Ong et al., 2004) (i.e. [cm cm-3]), showing the abundance
of roots. RLD is a “parameter of competitiveness“ (Schroth, 1999) or “quantifies
the capacity of the root system to explore soil volume“ and may have 1 cm cm-3 in
Musa, thus similar to trees; although herbaceous species may have 4-50 cm cm-3
(Turner, 2005). Other parameters of root efficiency and competitiveness are (a.o.)
age, diameter, root hair presence, physiological characteristics (Schroth, 1999).
Given that, high RLD accordingly represents high relative competitiveness (Turner,
2005; Schroth, 1999). Accordingly, “leaf area index and extinction coefficients“ in
the mixed canopy would define radiation competition, and biomass production is a
function of growth resource availability “in space and time“ (Ong et al., 2004).
Physiologically active and functional (fine) roots are of < 2 mm diameter; the
contrary structural, large roots account for approx. 90% of total root biomass, and
< 5% of root length (Akinnifesi et al., 2004). Therefor, the relative competitiveness
of root activity is better resembled by root length, than root (dry) biomass
(compare in Tab. 1). Stratification of Musa roots in soil see in Chapter 1.2. In
coffee, var. ‘Caturra‘, Siles et al. (2010) found 75% of total fine roots in 100 cm
from ground surface within the 60 cm topsoil, and homogeneously distributed,
even so in combination with Inga densiflora shade trees. Muñoz and Beer (2001)
had 50% of fine roots in 0-15 cm topsoil in Theobroma cacao combined with
20
Tab. 1 Components of the Musa root system, in length and biomass compared, different references
summarised.
Reference
Araya, 2005
Swennen et al., 1988
fine (<1 mm d.) thin (1-5 mm d.) thick (> 5 mm d.) contribution to total root system biomass
11 % 66 % 21 % 10 plantsAAA ʻGros Michelʻ
primary roots secondary laterals tertiary laterals contribution to length of whole root system
negligible: < 1%22 % 77 % AAA banana
negligible: < 1%53 % 46 % AAB plantain
Erythrina poeppigiana shade trees. The fine root distribution with the soil space is
a major aspect of compatibility of species (Khanna, 1998). Laterals of Musa
supposedly are more responsive than root axes, thus more conclusive in terms of
root architectural plasticity and adaption (Draye et al., 2005). Tree roots may
spread vertical and lateral, though the functional roots are closer to the trunk than
the whole lateral spread (Akinnifesi et al., 2004). Next to crop supply, roots have
functions like providing anchorage, improving soil conditions and providing organic
matter (Young, 1997; Araya, 2005).
Fine roots are likely for many crops and trees to be found in water rich, nutrient
rich soil layers, mostly the first 30 cm of the topsoil (Rao et al., 2004; Young, 1997,
Muschler 1993), particularly in the humid tropics (Beer et al., 1998). Mulching
causes fine root formation in the superficial soil layer, which results in competition,
once the additional biomass is decomposed (Rao et al., 2004; Schroth, 1999).
Erythrina poeppigiana litter decomposes fast, releases most nutrients < 4 weeks
(humid tropical conditions), and has approx. 3,3 %N (Nair, 1993). Trees may shift
the functionality of their fine roots short-termed (water availability), so that the high
RLD measured may not show the strongest active part (Rao et al., 2004). Acidic or
compacted soils as well can cause shallow tree root systems (Rao et al., 2004),
such as strong acidity of pH 4,5 - 4,7 (Akinnifesi et al., 2004), but perennials are
less affected by compaction (Akinnifesi et al., 2004), for Musa see in Chapter 1.2.
Other restricting influences are anoxia or soil temperature extremes (Akinnifesi et
21
al., 2004). Root formation is highly site specific (Blomme, 2000a, et al., 2000b;
Mukasa et al., 2005), as genotype and environmental factors interact (Schroth,
1999). Most often, trees and crops occupy the same soil layers, thus inevitable
competition arises (Rao et al., 2004), as most trees have many roots in the topsoil,
and then exponentially decreasing root systems with depth (Young, 1997;
Akinnifesi et al., 2004), although of many tropical trees are not well known
(Akinnifesi et al., 2004) and though spatial separation would be desirable (Beer et
al., 1998). Schroth (1999) reports that in multiple occupied soil layers, roots
appear to segregate with respect to their species, thus preferring higher intra-
specific to inter-specific root density; the mechanism why remains unclear, it
seems to be a kind of rhizospheric effect; Khanna (1998) says the sheer presence
seems to be repulsive. Schroth (1999) suggests, that zones depleted by
associated crops are infertile, thus the ‘compensatory root growth‘ initiates growth
into more fertile zones. Optimal would be a root system below the zones occupied
by shallow crops, like shallow banana mats, which could act as a ‘safety-net‘ and
‘rescue‘ nutrients from deep soil layers (Young, 1997; Akinnifesi et al., 2004). Rao
et al. (2004) suggest an optimal use of below-ground recourses, if the plant
components can occupy separated niches, such as “vertical, horizontal, temporal
and functional“ ones, in case the ‘functional diversity‘ of the plant species is given
by their ‘complementary root properties‘. But: in case root systems are not
competitive enough to displace others, an intermingling will be inevitable (Schroth,
1999). Diminished root systems due to missing space may reduce growth and thus
yield (Akinnifesi et al., 2004). Denser planting of trees leads to formation of deeper
root systems (Rao et al., 2004; Akinnifesi et al., 2004), though shallower rooted
crops have no possibility to ‘escape‘ (Muschler, 1993). Plants may pronounce
rather the vertical than their horizontal features (Noordwijk et al., 2004).
Root competition, measured by root abundance, thus is the shared access to
growth resources (Khanna, 1998). Competition present is that (A.) the depletion of
soil by other species, thus reduced resource availability (B.) the declined depletion
zone size per root, when total RLD increases, both intra- and inter-specific; (C.)
together with the plants demand defines its RLD its “relative competitive strength“;
and it may be increased by mycorrhiza associations (Cadisch et al., 2004).
22
Schroth (1999) and Akinnifesi et al. (2004) say that “depletion zones overlap“, thus
two-way intra-specific competition increases. Structural massive roots (trees)
seldom provide obstructive barriers to other species roots (Akinnifesi et al., 2004).
But scientists express the opinion that root presence may not necessarily indicate
competitive situations; Akinnifesi et al. (2004) e.g. see that even though tree roots
are abundant in the crop rooting zone, this does not need to be strong competition.
In experiments by Hamblin and Tennant (1987), the RLD of monocotyledonous
plants (cereals) exceeded those of dicotyledonous plants (legumes) by 5-10 times,
although shoot growth and soil water changes in rooting zones were similar. The
authors found also that the total RLD was not well correlated to water loss, as fine
RLD is not directly proportional to root functions. Schroth (1999) states that uptake
efficiency per unit root length differs. The RLD of trees often exceed that of crops
(Rao et al., 2004), especially between old, established trees and young, (possibly
annual) crops (Young, 1997).
Relative competitiveness of one species‘ roots is then influenced by their (possibly
stronger) vigour, which may be determined by the (then lower) specific root length
(SRL, i.e. [cm g-1]), thus better penetration of soils with root impedance (Akinnifesi
et al., 2004). Turner (2005) formulates, SRL “quantifies length of root per unit of
carbon invested in the root system“, may be 0,4 - 150 m g-1 for Musa, and is
influenced by climatic and edaphic conditions (Blomme, 2000a). Quite contrary to
the first sentence above, Akinnifesi et al. (2004) indicates, that high SRL shows
“greater plasticity in root growth and a better physiological capacity for water and
nutrient uptake“ (also: Blomme, 2000a), though less resilient to soil compaction
and water stress. Root systems hindered in their extent, thus lower total root
length and biomass, may show an increased SRL (Akinnifesi et al., 2004). Anyway,
Lecompte et al. (2005) finds the root diameter to be affected by carbon supply and
competition, thus positively correlated to light availability. Thinner roots are more
flexible (Schroth, 1999). Blomme (2000a) sees the uptake functions rather related
to more length than greater volume (VOL) of roots.
Plasticity of root systems thus is an important factor determining below-ground
competition (and is the key to assure a desired root behaviour, e.g. in Musa:
23
Draye, 2002). Especially for perennial plant components, competition can rather
be seen as long-term strategic opponents (Noordwijk et al., 2004). Time therefor is
so particularly important for roots, (A.) long-term field experiments (Rao et al.,
2004), (B.) as roots underlie a constant dynamic change in time and space
(Noordwijk et al., 2004). The author says the whole root system equals a
‘functional equilibrium‘, in which constantly root growth and root mortality balance
its size (Fig. 2); this dynamics enable responses to local stimulants, with specific
“velocity and intensity“. Plasticity in responses to edaphic and environmental
conditions include other root systems, and mean changing growth and
physiological characteristics (Schroth, 1999). They may become vertical, so the
author, instead of horizontal; but it requires flexibility, competitiveness, deep soils
and partial shallowness; otherwise they intermingle, what could be desirable if N2-
fixing species are involved. The ‘standing root biomass‘ of established perennials
changes little (Fig. 2), and though Noordwijk et al. (2004) states a far higher
plasticity in below-ground plant biomass than above-ground. Early success or
failure, as the first year of establishment of bananas in those plots certainly would
qualify for, do not indicate necessarily the long-term potential of the system as
plants develop with age (Rao et al., 1998, Kenzo et al., 2010). Established tree
root systems often are pre-dominantly competitive to young established crops,
especially in limiting conditions (Akinnifesi et al., 2004; Schroth, 1999), and tree
root densities increase with their age (Rao et al., 2004), as does competition
(Khanna, 1998). In mature plantations of cacao and Erythrina poeppigiana,
Fig. 2 Growth and decay of roots in perennials (trees) and annual crops, schematic (Noordwijk et al., 2004, p.
84)
24
Muñoz and Beer (2001) found annual turnover close to 1.0 of fine roots, and
assumed a constant annual rate, and thus 3-6% nutrient input only by turnover.
Banana and plantain root systems have major constituents being ‘transient‘
structures. Root axes live approx. 2-6 months; primary laterals persist for 6-10
days to 8 weeks, secondary up to 5 weeks and root hairs for approx. 3 weeks
(Draye, 2002). The author mentions a decay of root hairs, if root axes in their
growth are arrested; thus, edaphic conditions declining their growth are important
in intensive cropping systems (Draye et al., 2005). The maximal root system size
has a Musa at flowering, then root growth decays; and that roots have to fulfil all
shoot demands (Blomme, 2000a). The ‘plant crop‘ is the first harvest cycle,
followed by ‘ratoon crops‘ (second harvest cycle onwards), and the vegetative
reproduction has some consequences for production. Robinson and Nel (1989)
found sub-optimal competition until the 2nd ratoon cycle, then onwards accordingly
increasing plant parameter magnitudes, including yield (see Chapter 1.2). Carr
(2009) suggests that optimal planting densities for plant cycles and ratoon cycles
differ. Depending upon the sucker chosen for each ratoon cycle, the plant
becomes ‘nomadic‘, i.e. it changes position (Blomme, 2000a; Carr, 2009). Suckers
develop first root axes before the mother plant decays (up to 200-300 apiece;
Draye et al., 2005), thus the plant includes actually several root systems, a shared
common pool of growth resources for both, and those several individual root
systems architecture and functioning has to be considered in planting system
balances (Blomme, 2000a). Given that, the later ratoon cycles are of increased
importance to evaluate a plant combination or density.
Above- and below-ground
Above- and below-ground interactions may be difficult to separate (Muschler,
1993), and valuing beneficial interactions and improvements by planting
combinations, that may not be quantifiable, as well (Akinnifesi et al., 2004).
Though, connecting causes and effects in dense agroecosystems is necessary to
understand their complexity; research in this aspect thus is a consideration of
choices. Ong et al. (2004) find that yield losses may be accepted as costly
‘structural investment‘ in turn, and productivity and sustainability are interrelated.
25
Robinson and Nel (1989) found high overlapping spatial arrangements of bananas
in plantations advantageous in easier plant access and mechanical bunch support,
by their arrangement, what “compensates the physiologically induced yield
reduction“, especially if that is low as in their experiment observed.
A plant forms a ‘functional equilibrium‘12 between its below- and above-ground
parts (Noordwijk et al., 2004), suspected for Musa early by Swennen (1984). In a
case, where nutrients or water may be scarce, the equilibrium is shifted towards
more root formation. Better access to scarce resources and less above-ground
biomass demanding growth resources still balances the plant a functional unit. In
another case, where irradiance by the sun may be reduced, it will shift towards
more leaf formation. More leaf area to capture radiation and less roots demanding
photosynthates - carbohydrates - will keep the plant functioning (Noordwijk et al.,
2004). Yields could be at risk, if the balance is shifted unfavourably - e.g. if root
system under stress require largest quantities of photosynthates - and often
unfavourable conditions reduce both root and shoot growth (Akinnifesi et al., 2004;
Blomme, 2000a). Highly generalised, scientists say that roots account for about
one third of a total plants carbon content (Nair, 1993); or 14 - 16% of total biomass
(in an secondary forest, Kenzo et al., 2010); or approx. 20-30% of total biomass,
15% in humid, 50% in arid regions (Nair, 1993), or 20% of coffee var.
‘Caturra‘ (Siles et al., 2010). Ratios may quantify that equilibrium, though literature
provides them both on shoot or root basis. We used shoot : root ratios (root
biomass basis), according to Blomme (2000a), et al. (2000b) and Young (1997).
Those are approx. 1-4 for trees, in a generalised expectation (Young, 1997; for
bananas, see above), or 1-8 (Noordwijk et al., 2004); and a higher shoot : root
ratio for the arable component is considered useful (Akinnifesi et al., 2004).
That plant-inherent mechanism is renowned used for managing trees in crops,
especially leguminous shade trees in perennial crops (Schroth, 1999). Pruning the
26
12 Indeed, Noordwijk et al. (2004) use the term ʻfunctional equilibriumʻ to describe both the unit ʻplantʻ, and the unit ʻroot systemʻ. In both cases, the plant organs form functional units, that continuously change in time (dynamics) and mostly in space, too, during the plantsʻ life. The description for the Musa ʻplantʻ is used by Swennen (1984) too.
shoots of a shade tree reduces their root competitiveness. Roots are reduced to
save carbon, as their is less shoot to support roots, and no shoot biomass
demanding as much nutrient and water uptake as before. Roots ‘die-back‘, and
provide additional organic matter; the root system is less flexible; shade is
managed by pruning and the residues, used as green manure, add to the soil
nutrient pool, but old trees will response less (Rao et al., 2004; Schroth, 1999).
A most essential question is: “How much root system does the (a) plant need“?
(Noordwijk et al., 2004, Nair 1990, Akinnifesi et al., 2004). It must be answered as
a producers decision, which plant component in a mixed-species system is
economically used (Schroth, 1999; Beer et al., 1998). ‘Only‘ shade-providing
service-trees might be degraded thus in their importance. Although, as they take
place away, there has to be any positive (economic or other) effect; as they require
- even if well-managed and uncompetitive - space, light, soil resources and
manpower (Schroth, 1999). Second, the yield of a crop may be economically or
domestically sufficient, even though individual root systems remain small (Schroth,
1999; Noordwijk et al., 2004). That is, again, a socio-economic decision, but also a
specific consideration of plant productivity (for Musa - Chapter 1.2, p. 15). In Musa,
e.g., carbohydrates may as well be spent on fruit tissues instead of extensive root
growth, when the rooting zone is well supplied (Blomme, 2000a). Though, forming
extensive root system even without a productive need may raise competitiveness
within a densely spaced system (Noordwijk et al., 2004). Hence, a ‘competitive
balance‘ must be found for a certain combination of species, whether that is ‘ideal‘
in a theoretical sense or not.
Species and combination
Coffee is often grown commercially with (leguminous) local shade tree species,
such as Eucalyptus spp., Erythrina spp., Inga densiflora etc. in Central America
(Schaller et al., 2003a; Schroth, 1999; Siles et al., 2010), as are other perennial
crops as well (Muñoz and Beer, 2001). Bananas are quite frequently intercropped,
especially in home gardens and for regional supply13. Bananas are taller than
27
13 Base-line study of farms for the Bioversity International project: see Dold (2010).
coffee shrubs with wide spread leaves, why they are partially used as shade to
coffee (Beer et al., 1998), due to size and their higher affinity to strong radiation. A
banana canopy may absorb 90% of incoming radiation (Turner et al., 2007). The
system may be problematic, as bananas are very sensitive to wind and their
falling, maybe during harvest, is suspected to damage the coffee (Beer et al.,
1998). The author reviewed two late studies and found strong competition
between both species. The infestation with the Pratylenchus coffeae nematode
may increase, as banana is a host as well as coffee (Desaeger et al., 2004).
Schroth (1999) suggested to avoid root competition amongst the perennial species
as far as possible - positive edaphic effects, that shade tree root systems provide,
are already given by the perennial crop root systems.
Erythrina poeppigiana (‘Poró‘), is a fast-growing nitrogen-fixing tree, which is used
as a mere ‘service tree‘ (Muñoz and Beer, 2001) as it provides only functions
beneficial to adjacent crops, like shade, green manure and soil improvement (Nair
1993), but neither is used as timber or the production of any valuable product.
Such ‘FGNFT‘s‘ (Young, 1997) are said to have more aggressive roots than slow-
growing trees (Rao et al., 2004); and Cadisch et al. (2004) considers deeper
rooting and less competitive species to be possibly more useful than ‘FGNFT‘s‘ in
these systems. Fast-growth of trees is not necessarily related to strong
competitiveness (Schroth, 1999), although often presumed (Schaller et al., 2003a).
Though, Central American farmer use it frequently in coffee; it was observed, that
the tree species used are changed responsive to coffee price situations by the
farmers (Schaller et al., 2003a; Beer et al., 1998). N2-fixation rates were approx.
60 kg ha-1 year-1 (Nair, 1990; 1993; Beer et al., 1998), and nitrogen transfer is by
its prunings and litter being laid as green manure upon the soil surface (Khanna,
1998), and by its root die-back and nodule senescence (Young, 1997; Muschler
1993; Khanna, 1998), though nitrogen content in nodules is anticipated to be small
compared to other tree parts, yet faster in decomposition (Nair, 1993; Beer et al.,
1998). Pruning the shoots of Erythrina poeppigiana causes a decline of root
activity (Muschler, 1993), making it manipulatable for resource competition, and
causes a downright nodule mortality rather than common senescence (Mafongoya
et al., 2004). Thus, N2-fixation was observed to require 10 weeks to reach pre-
28
pruning rates, and a total suppression under excessive pruning was feared
(Mafongoya et al., 2004), as that may cause an increased demand for mineral N
sources. “The large, spherical nodules are clustered on the central root system, ...
with the highest weight closely to the stem of the tree“ (Nair, 1993). That may
indicate the preferred fixation-areas in soil. Muschler (1993) expects nodules of
trees to be in equal ‘mineral-rich topsoil‘ than fine roots. Erythrina poeppigiana is
acidity-tolerant (Nair, 1993) and was shown to have functional fine root contents in
intermediary soil layers (neither shallow nor deep, Rao et al., 2004), though fast-
growing tree species are said to have deep, extensive root systems (Akinnifesi et
al., 2004). The strong removal of soil resources and fixing in its own biomass may
occur (Nair, 1993), though, here the trees are yet established and their biomass as
green manure re-used.
The coffee variety grown here is ‘Caturra‘, which is “a highly productive dwarf
variety“ (Siles et al., 2010); the author says it depends upon quite strong
fertilisation to maintain the high productivity. Coffee can well be grown in 40-70%
shade (Beer et al., 1998), as coffee may have developed understory (Schaller et
al., 2003a) and Siles et al. (2010) found 30% yield reduction in coffee with less
than 40% light availability, shaded by Inga densiflora; yet the shaded coffee
harvest is of high quality. In the same experiments, the author saw no fundamental
effects on the biomass of coffee, though the leaf characteristics changed much.
Coffee removed from full sun is less physiologically stressed (Siles et al., 2010),
thus being less affected by certain diseases (Desaeger et al., 2004). Scientists
suggest, that coffee grown on optimal sites under shade produces less yield, but
under limited conditions produces better yields in shade than under full sun (Beer
et al., 1998); yet the Central Valley is a quite optimal growing condition (Siles et
al., 2010). Coffee photosynthesis rates are maximal in intermediate shade and it is
high temperature-sensitive (Beer et al., 1998). Coffee root systems seem
competitive enough to displace tree root systems (Schaller et al., 2003a). Siles et
al. (2010) found 50% of the fine roots of coffee in the topmost 60cm inter-row to
coffee rows, whereas in combination with Inga densiflora, it were 70%; if the tree
densities are to high and the trees are not managed (canopy closure), the yield of
coffee will be stronger reduced.
29
The growing system of coffee and Erythrina poeppigiana received quite some
research attention, indicating, that their nutrient cycling within the agroecosystem
is rather closed (reviewed by Nair, 1993; Young, 1997), but the Musa plants are
anticipated to change that balance considerably, especially because their high
amount of fruit tissues is harvested and removed. Water competition is likely for
simultaneous dense systems, but in < 800 or < 1000 mm rainfall conditions
(Young, 1997). Rainfall in Turrialba exceeds 3200 mm (Chapter 3.1; CATIE
meteorological data), thus we do not anticipate a direct water competition. Beer et
al. (1998) says that short dry periods already may cause water competition, even
in humid tropics; but the dry season of Turrialba is rather indistinctive. Bananas
are most depended upon a well balanced water supply, maybe most of all possible
biophysical factors (Carr, 2009). Turner et al. (2007) admits, that the sensitivity of
Musa to water was over-issued often, and there is a considerable drought
tolerance anyhow, for shorter dry periods and possibly related to the ‘B‘ genome;
leaf folding and stomata closure are Musa adjusting mechanisms. Mixed-species
systems are highly complex in their interactions, as they have direct competition
(Rao et al., 1998; and 2004).
Schaller et al. (2003a) studied Coffea arabica and Eucalyptus deglupta, grown in a
commercial finca (‘Juan Viño‘), situated between Turrialba and Cartago. The
authors concluded, that their mixed-species systems worked well, because A.
more growth resources than required were available; B. trees and coffee shrubs
used the resources complementary, as their roots were complementary distributed
(coffee-row and inter-row); and C. coffee root systems were apparently sufficiently
competitive to stand their ground against the trees. The authors found, that the
total RLD was very similar across the plots, so that the soil space seemed very
efficiently used.
„Optimum planting density for bananas is derived from a complex integration of
many factors, all of which must be evaluated for each individual
plantation“ (Robinson and Nel, 1988). Robinson and Nel (1989) measured the
influence of spatial AAA Cavendish ‘Williams‘ arrangements upon vegetative and
yield components. Significantly the bunch mass was reduced (up to 9%), the more
30
individual plants overlapped within the system, but not before the 2nd ratoon cycle
(i.e. third harvest cycle). Standard recommended densities according to the
authors were 1666 plants ha-1. The productivity (yield year-1) was non-significantly
lower for higher overlapping (up to 7,4%), but more determined by bunch mass
than the not-consistently elongated crop cycles. According to Draye (2002) and et
al. (2005), high planting densities promote root formation, whereas low
temperatures arrest root growth. The ‘nomadic‘ habit of perennials reproduced by
ratoons (Blomme, 2000a) complicates finding complementary planting
arrangements. Increased competition, e.g. in terms of water, causes higher plant
to plant variability (Carr, 2009), which may influence sampling. The author adds
that optimum density may depend upon which cultivars and conditions are applied.
1.4 Root sampling methods
Root access
Roots may be tested in vitro or in vivo (Blomme, 2000a; Swennen, 1984). Though
in vitro has the advantage of being comparable to other studies, which is hardly
possible for the global range of environmental conditions of field studies, their
conclusion may be limited (Draye, 2002); but roots are 95% healthy (Swennen,
1984). A plant within a complex agroecosystem will most probably develop
differently, and such direct insight a field experiment provides. Field condition
sampling is most laborious and difficult in terms of assessing the whole root
system (Blomme, 2000a; et al., 2000b; et al., 2005). Draye (2002) sees field
studies limited in giving information about banana root systems as well, except for
monitoring complete crop cycles, and suggests controlled experiments for
understanding phenotypic responses. The authors major concerns are root traits
to be studied in field are limited, the size of core samples would have to be very
large for the spatial variability banana root systems provide.
Many on-field experimental methods modify the growing environment of the plant
studied, thus results may be biased; such are e.g. (mini-) rhizotrons, i.e. glass
walls or in-growth tubes (Blomme, 2000a); or sector sampling and trench profiles
31
(Draye et al., 2005). Excavations, trenching or profile walls are “time consuming
and destructive“, so the author. Schaller et al. (2003b) excavated 0,8 x 3 m profile
walls completely around trees; Araya (2005) excavated in quarter circles around
the Musa plants. Destructed sites may not be evaluated a second time without
intrusion in plant growth. Early plant development (young) did not provide
conclusions for mature plants (Blomme 2000a; et al., 2005). Thus, Turner et al.
(2007) reported simulations and ‘allometric relationships‘, which were sought
within the plant, to explain root traits by observing shoot traits (Swennen, 1984;
Blomme, 2000a; et al., 2000b; Mukasa et al., 2005; Draye, 2002); though that
models were not universal, as shoot- and root composition of plants changes due
to maturity stages and environmental conditions (Blomme et al., 2005).
Simulations design the activity of any root meristem in both time and space (Draye
et al., 2005).
Alternative: non-destructively
In an attempt to find those alternative methods to assess banana roots, Blomme
(2000a); and published et al., (2000b), et al. (2005) tried several comprehensive
possibilities. Significant positive relations were found (Tab. 2), e.g. best for
pseudostem height and leaf area. The author subdued the data to equations
gained by Regression Analysis. Those explained at least 90% of the root variation
by shoot characteristics; with leaf area and pseudostem circumference among the
best shoot traits to use; leading to R2 = 0,93 for total root mat dry weight and R2 =
0,97 for average cord root basal diameter. Carr (2009) reviewed similar relations
Tab. 2 Root and shoot traits related by Correlation Coefficients in 20 week old plants, grown in field at 2x2 m
spacing, 27 Musa genotypes (Blomme, 2000a, shortened, p. 107). Significant at P < 0,001; ** P < 0,01; * P <
0,05; (n.s.) = not significant.
Traits Leaf area[cm2]
Plant height[cm]
Plant circumference [cm]
Root dry weight [g]
Cord root length [cm]
Av. basal cord r. diameter [mm]
Total dry weight [g]
0,72 0,65 0,65
0,64 0,54 ** 0,46 *
0,47 * 0,51 ** 0,70
0,65 0,53 ** 0,38 (n.s.)
32
being positively linear between pseudostem diameter and female flower number
(r2 = 81%), and diameter increase and female flower production (r2 = 85%).
Serrano (2005) reports own published results, in which functional root weight was
correlated with 0,85 or 0,92 with annual yield (boxes). Turner et al. (2007) notes
that for any simulative calculations the difficulty is to fit them into fields, where
roots grow in remarkable variations in time and space. Draye (2002) analogue
adds those relations to be of seasonal or possibly genome induced variation.
Ratios are a useful tool to compare changes and balances in components, as
shoot and root parts of a Musa plant, the ‘functional equilibrium‘, indicated by
(Swennen, 1984). Blomme (2000a) sees ‘absolute‘ data required, i.e. the total root
mat has to be measured. Shoot-root ratios are expected to change significantly in
environmental impacts, possibly for genotypes and in course of vegetative and
reproductive cycles (Blomme et al., 2000b). In that publication, the author showed
the developmental stage influencing the shoot and root compounds of Musa plants
(Fig. 3 A.), and the arrows show the sampling age of the Musa plants in the study
at hand (6 months). Shoot-root ratios were assessed for several Musa genotypes
(Fig. 3 B.)
Coring
Coring has known methodological weaknesses, such as high variability in results
in terms of enormous standard errors (Noordwijk et al., 2004), and the small soil
volume taken compared to the high spatial variability of (e.g.) tree root systems
(Akinnifesi et al., 2004), and soil site volume generally being highly heterogeneous
(Araya, 2005). For monitoring root development over time, i.e. ‘sequential‘, they
are even rather less usable; quite comprehensible, as the destruction of root
system to gather early sampling series will necessarily influence later sampling
series (Noordwijk et al., 2004). Though, in Musa studies, they were used to be
anticipated an easy-to-use, one-time and on-farm-compatible method (Draye et
al., 2005), so there were ways sought to further minimise their difficulties. Any form
of sampling demanding soil-root separation may suffer root loss (Blomme, 2000a).
Important for coring in Musa, so Draye et al. (2005), is the proximity to the plant (<
30cm), the individual core size and their total number. In a virtual (!) coring
33
Fig. 3 Shoot-root ratios of nine Musa genotypes at flowering of the first crop cycle (A.), and dry matter
distribution of two varieties from planting to harvest (B.). Genome groups: AA (‘Calcutta 4‘); AAA (‘Valery‘);
AAB (‘Agbagba‘, ‘Mbi Egome‘, ‘Obino l‘Ewai‘); ABB (‘Cardaba‘) and three “tetraploid plantain hybrids“. FL =
flower emergence; arrows = sampling date in our study at hand (approx. 6 months). (Blomme et al., 2000b;
modified, p. 16)
experiment, the authors detected a high variability of Musa roots in space, even
though 90 root systems were designed out of the same root number and length;
that variability was to be seen in the cores as well. Araya (2005) suggests cores of
15 x 15 x 30 cm; if taken at the area of highest root length density (RLD) around
the Musa plant, their size may be reduced to the smallest possible.
Blomme (2000a) designed rather large ‘cores‘, compared to standard augers,
which were excavated by small spades (Fig. 4). Wild banana AA ‘Calcutta 4‘ and
AAB plantain ‘Mbi Egome‘ were planted at 4 x 4 m, cores were located in the first
60cm from the plant suspected to host most of the root system. The author
detected the cores to show 1,1 - 1,4% for root dry weight [g], and 2,2 - 2,7% for
cord root number and cord root length [cm]. Both interplant variation and core
location was found to be significant once, which was interpreted to indicate the
high spatial variability of the root system, especially for suckering behaviour. All
three traits showed R2 > 0,86 in average for double samples (two cores related to
34
B.A.
Fig. 4 In Blomme (2000a, p. 110) used method of soil core sample arrangement. First core according to axial
line through mother plant (MP) and biggest sucker (BS), at 15cm from the mat, and intervals at 45°. Size:
diameter 25cm and height 80cm.
the whole mat), and even more for triple cores for both genotypes. In a second
study of 30 genotypes, core values could explain 80% (double core) and 85%
(triple core) of the whole root mat. Mukasa et al. (2005) continued the work in
different edaphic conditions, and in Uganda instead of Nigeria. Eight genotypes of
Musa were assessed on-farm by the same method, only reduced to three cores
per plant. The cores showed 5,2 - 8,1% for root dry weight [g], and 6,3 - 7,1% for
cord root length [cm]. Thus, the author concludes, maybe the compact loamy soils
of the Uganda-sites restricted root spread stronger than the sandy Nigerian soil,
and therefor more roots were found within shorter distance of the Musa plant, and
therefor within the cores. The variability was higher amongst plants than core
locations.
Those coring systems spread around individual Musa plants serve to understand
the banana root growth in the first place, even though Erythrina poeppigiana and
Coffea arabica roots may be quantified and analysed within the cores. Samples of
core sizes around trees even are suspicious because of the high spatial variability
of the tree root system, states Noordwijk et al. (2004). Despite that concern, the
following studies were conducted in over-the-whole-plot patterns:
35
Siles et al. (2010) chose diagonal core sampling patterns across their plots, in
mixed-species systems of Coffea arabica and Inga densiflora (shade tree).
Positions of cores were A. characterised by their distance to the nearest shade
tree, and B. whether located within the coffee-row or the inter-row. Sampling depth
was 1 m, and both species‘ root were not separated. In a control system of pure
coffee shrubs, as well as in the combined mixed-systems, most fine roots were
found within the coffee rows, and a marked decline in the inter-rows.
Muñoz and Beer (2001) divided their plots in 1 m2 units, that were classified
according to their distance to the shade trees. In mixed-species systems of
Theobroma cacao (perennial) and Erythrina poeppigiana (shade tree) were soil
cores taken, and in a second series in-growth bags installed. A 0,5 mm grid was
used for separating roots from soil, and fine roots < 2mm were analysed. Dead
roots were not excluded. No significant differences in root abundances occurred in
the 15 cm topsoil.
Schaller et al. (2003a) used again a diagonal pattern across their plots, in mixed-
species systems of Coffea arabica (2 x 1 m2) and Eucalyptus deglupta (shade
tree; 8 x 8 m2 spacing). Cores were defined with respect to season, soil depth,
distance from shade trees and positioning referring to the coffee row, in a series of
different studies. A number of equal positioned samples were bulked and a
representative core created. A 0,5 mm sieve was used, and fine RLD < 2 mm was
measured. In second series, the positions were displaced to avoid disturbed soil.
Sampling depth was 40 cm. 63% of the tree roots were in the topsoil, whereas
only 40% coffee roots, but those were homogeneously distributed in the upper 40
cm. Coffee roots do not significantly de- or in-crease in proximity or periphery of
shade trees. Coffee roots are found within the coffee rows, with a marked decline
in inter-rows; and Eucalyptus deglupta seems to be quite the contrary. No effect of
shade trees on coffee growth and yield was observed. In another publication,
Schaller et al. (2003b) analysed roots up to > 10 mm diameter in different classes,
within large trenched profile walls; and only fine roots < 2 mm in taken cores, in a
mixed-species system of Eucalyptus deglupta and grass contour stripes.
36
2. Hypotheses
Objective A
Natural shading impact on Musa cultivar root formation and distribution.
1. Biomass allocation. Banana and plantain have less root biomass in high levels
of natural shading (Chapter 6.1). The Shoot-root ratio of each plant increases,
because the root biomass is stronger reduced than the shoot biomass (Chapter
7.2). Genotypic differences cause a variation in phenotypic responses to the
named conditions.
2. Spatial proliferation. The density and amount of Musa roots decreases in
horizontal (distance) and vertical (depth) directions from the rhizome (Chapter
6.1.2). In high natural shade, the banana root distribution is shortened more,
thus, the amount of roots of adjacent plants increases (Chapter 6.2). Genotypic
differences lead to varying phenotypic root formation.
3. Correlated parameters. Shoot characteristics and root traits are strongly
positively correlated (Chapter 7.1.2). Environmental conditions are correlated to
banana root traits (Chapter 7.1.1). Root density and amount of coffee and tree
roots are strongly negatively correlated to banana roots (Chapter 6.2.2).
Genotypic differences are assumed.
Objective B
Soil core sampling methods for field grown banana root assessment.
4. Sampling methods. Large samples (monoliths) are qualitatively more precise
(standard errors) than small samples (auger) (Chapter 5.2). Small samples are
advantageous in dense planting system field conditions, whereas large samples
suit better to the spatial structure of banana root systems (Chapter 5.1).
37
3. Experimental sites
Climate and edaphic conditions are factors influencing phenotypic plant
development strongly (Turner et al., 2007). The experimental fields in which we
grew Musa for studying were designed before my root studies, as they served for
more observations in terms of photosynthesis, leaf area and earthworms (fellow
colleagues). Thus, their design and layout shall be introduced shortly.
3.1 Geography and climate
Turrialba is located submontane to a volcano in the Central Valley of Costa Rica.
The small country is bordered by Atlantic and Pacific shores. The highlands are of
mostly volcanic origin and reach altitudes up to 3300 m a.s.l. Costa Rica can be
divided into several climatic zones. Generally, it is situated in the equatorial zone
providing tropical climate (CATIE Meteorological Data). Mostly, two seasons can
be distinguished in different durations and characteristics. Costa Rica is
characterised by14 its high temperatures and commonly much rain, whereas
humidity varies. The Central Valley reaches middle temperatures of 22 °C, i.e. 72
°F, all year, i.e. milder than in costal lowlands. The small size makes it prone to
winds and sea breezes.
Turrialba is situated at 602 m a.s.l. at the coordinates 9° 53‘ latitude north and 83°
38‘ longitude east (CATIE Meteorological Data). Two seasons form a year. Its dry
season should last from late December to March and its rainy season from late
April or May to November. It endures a tropical warm climate with a dry season, as
well as other Costa Rica parts. But in the highlands, average temperatures are
lower. The measuring station is located directly in the middle of the CATIE
campus. In 2010, the wet season started considerably late, not before the middle
of May. It lasted longer as well, until the second week of January, more or less. For
38
14 If not otherwise named: all (!) meteorological and climatic data/ information were taken from CATIE Meteorological services, http://www.catie.ac.cr/, “Services“. Date of access April 2011. For further climatic information consider www.imn.ac.cr, the Instituto Meteorológico Nacional, IMN.
its ca. 9 to 10 months rain it is a humid warm tropical climate, with approx. 3274,2
mm rain in 2010 (calculated from Tab. 3).15
The field work for this study took place from 31 August 2010 to middle of
December 2010 (meteorological data 2010: Tab. 3). Although January and
February show a quite high precipitation referring to the fact it is the ‘dry‘ season,
the number of days with an amount of rain above 0,1 mm is lower than for the ‘wet‘
season months (CATIE ‘Monthly Summary of the Year 2010‘, not shown).16
Tab. 3 Monthly average values of temperature, relative humidity and solar radiation (per day), as well as total
precipitation per month, of year 2010. Additional yearly average values for each parameter since the
beginning of observations, i.e. Temperature 1958, Precipitation 1942, relative humidity 1958, solar radiation
1968. Values in brackets include 2010, regular value only until 2009. Data of meteorological station located at
CATIE, Turrialba, Costa Rica; data generated by CATIE.
Month Temperature [C°] Precipitation [mm] Rel. Humidity [%] Sol. Radiation [MJ/m2]
January
February
March
April
May
June
July
August
September
October
November
December
Average all years
20,9 255,7 92,2 14,7
22,0 252,1 93,2 15,5
22,2 224,4 92,6 16,6
23,1 179,9 91,9 16,9
23,3 183,2 93,3 17,1
22,9 276,8 93,3 16,9
22,9 167,8 92,7 16,7
22,9 292,1 92,9 17,3
22,5 360,3 93,0 12,2
22,5 133,6 92,3 16,1
21,2 299,0 94,2 13,1
20,0 649,3 95,2 11,5
21,8 (21,8) 224,4 (225,7) 88,1 (88,3) 16,8 (16,6)
39
15 Classification in Diercke World Atlas, 1996, Germany. Young (1997) provides criteria to classify climates as well; and 0 months with < 60 mm rain (ʻdryʻ) and > 1500 mm annual rainfall give evidence that Turrialba is ʻhumid tropicsʻ.
16 CATIE Meteorological Data, ʻMonthly Summary of the Year 2010ʻ, http://www.catie.ac.cr/ (see for Days > 0,1 mm precipitation). The ʻdryʻ season of Turrialba is relatively indistinctive.
3.2 Experimental plots
In the very vicinity of CATIE, an area of commercial use and scientific studies is
situated, ‘La finca comercial‘. Sugar cane and coffee are produced, and it hosts a
remarkable collection of cacao genotypes. The area used for the study at hand
belongs to Scientist Elias de Melo, and ‘La Molina‘ serves for organic coffee
production at ~ 5,27 ha, and approx. 1 ha was in our experiment (Zapata, 201017).
At any rate, coffee and shade trees are older than 35 years in this constellation,
with replanted individuals every now and then.
Fig. 5 ‘La Molina‘: Four levels of shade, including Musa spp. and Coffea arabica, shaded by mostly Erythrina
poeppigiana. From top left to bottom right: minimal shade (ca. 8%), 25% shade, 50% shade, 75% shade.
Situated at: CATIE, La finca comercial, Turrialba, Costa Rica.
40
17 The MSc student Zapata Padilla, C.D., characterised shade and soil conditions within CATIEʻs ʻfinca comercialʻ in his thesis. For ʻLa Molinaʻ, excluding our 1 ha banana treatment, he found: tree species are approx. 88 Cedars ha-1, and predominately 230 Poró ha-1; thus approx. 60% canopy closure; a “plant density“ - not specified, whether only coffee or all plants - of 5571 plants ha-1, a lower density compared to the others; an annual average 12,12, quintal ha-1 harvest. It can not be taken as a description of our four shade levels. It is additional information to the surroundings.
Two plots exists. The larger one was divided into three parts, forming 25%, 50%
and 75% natural shading by canopy closure of tall Erythrina poeppigiana trees
(Fig. 5), and very sporadic Cedars. It forms a soft depression, in particular at 75%
shade. The smaller one was made minimal natural shading, corresponding
approx. 8% of canopy closure. It lies on a small hill, exposing the soil to the sun
and descending in a soft slope.
The planting scheme of Coffea arabica, variety ‘Caturra‘, is equal for all four levels
of natural shade. The shade trees ‘Poró‘, i.e. Erythrina poeppigiana, are planted in
low densities (minimal shade) to high densities (75% shade), in rows parallel to
those of coffee. Poró‘s in lowest density had thicker stems and a lower canopy
than in the other three densities, crudely observed. The coffee berries are
continuously harvested, even during field work of studies. The shade trees were
pruned all three months, with a view to maintain the respective canopy closure of
each shade level. The pruned leaves were left in each part, whereas the woody
branches were removed.
Musa spp. plants were grown precisely in the coffee inter-rows, with a distance of
3 x 3 m between banana plants (Fig. 6), thus leaving one inter-row empty to avoid
banana roots intermingling nearby. Nine cultivars of Musa were distributed
Fig. 6 Basic planting scheme of Musa spp. mother plants and coffee rows of all four shade level plots. Shade
trees are additional, not shown, in parallel rows and densities due to each natural shade level.
41
randomly upon those planting locations, each in five replications per level of
shade. Four Musa cultivars were chose for root studies, the remaining cultivars
were left to enable other studies at full maturity and fruit ripening; the four cultivars
being the dessert bananas AAA ‘Gros Michel‘ and ‘Red (Makabu)‘, synonym
‘Morado‘, the cooking banana ABB ‘Pelipita‘, synonym ‘Filipita‘, and the plantain
AAB Curraré. In the study at hand, three replications were chosen per level of
shade to be sampled.
The above-ground situation, that means the natural shading and light conditions,
and the Musa spp. shoot characteristics, were gathered by A. Musa plant
measurements, and B. different kinds of data representing the surroundings. By
me, Musa pseudostem height, diameter and the number of suckers were
protocolled. Erwid Valdivia gathered quite some data within the framework of his
Master thesis. Used by me, that includes DIFN (diffuse light), LAI (leaf area index
of shade trees), TDR (soil humidity), and Musa spp. dry shoot biomass.
Tab. 4 Musa spp. plant measurements for twelve plants per cultivar, three per level of shade. Three cultivars
measured. PSH = pseudostem height, DIA = pseudostem diameter at 1m pseudostem height; SU = number of
suckers per mother plant. Plant in italics (Curraré 75%): was replanted for died plant, i.e. too young.
PSH [cm]PSH [cm]PSH [cm] DIA [cm]DIA [cm]DIA [cm] SUSUSU
Gros Michel
Curraré
Pelipita
Minimal 164,0 156,6 184,0 27,7 26,1 31,2 3 3 5
25 % 180,0 167,0 182,0 28,0 26,0 26,7 3 4 4
50 % 197,0 173,0 185,3 29,2 25,6 24,5 2 2 4
75 % 162,0 136,0 139,5 23,4 18,3 17,0 0 0 0
Minimal 200,0 136,5 254,3 34,4 22,1 47,2 3 0 5
25 % 226,7 197,0 149,0 40,2 32,5 23,7 5 3 1
50 % 172,0 168,0 199,0 25,0 27,5 32,0 0 1 3
75 % 151,0 100,4 149,0 25,2 10,1 18,5 0 0 0
Minimal 241,0 221,0 206,5 43,9 42,9 39,8 4 2 2
25 % 186,5 231,4 244,0 34,7 42,9 45,7 2 2 3
50 % 195,0 222,5 192,0 34,6 35,5 32,9 1 1 1
75 % 139,0 143,0 160,5 24,9 22,0 26,4 0 0 0
42
Musa shoot growth was quantified in a small data set directly prior to root
sampling. Pseudostem height was measured from the soil surface to the point of
parting of the last two new leaves, often including just unrolling leaves (Tab. 4).
Diameter, measured at 1 m height of the pseudostem, emerges simultaneously.
The number of suckers was counted, thus only those visible above soil surface
were included. Given that root sampling stretched above approx. 2,5 months time,
the cultivars were of different age at measuring, in order ‘Gros Michel‘ (youngest) -
‘Curraré‘ - (‘Morado‘, not measured) - ‘Pelipita‘ (oldest). A reduction in plant size
and diameter may be observed for high natural shading levels, 75% in particular,
as well as the continuous reduction in sucker numbers, to zero in 75% shading.
The Musa dry shoot biomass is not shown here (see Chapter 7.2). Erwid Valdivia
kindly made both Musa shoot biomass and the following environmental
parameters available; TDR may be seen in Chapter 3.3. The light conditions are
registered by DIFN, a method to quantify the diffuse light amount received among
a canopy, and the LAI of that canopy, which measures the amount of shading in
terms of leaf area per unit of ground. Thus, DIFN should be 1 for minimal shading
(∼full sun), where LAI should be zero; consequentially, DIFN should be zero for
Tab. 5 Light conditions in four shade levels, measurement located next to experimental Musa spp. plants.
DIFN = diffuse light, unit non-dimensional; LAI = leaf area index of shade trees, unit is [cm2 cm-2]; “n.a.“ = not
available. N = 3; values in italics: N = 2. Data kindly made available by Erwid Valdivia.
Gros Michel Curraré Morado Pelipita
DIFN
LAI
Minimal 1 1 1 1
25 % 0,67 0,67 0,60 n.a.
50 % 0,48 0,43 0,41 0,42
75 % 0,20 0,64 0,24 0,25
Minimal 0 0 0 0
25 % 0,56 0,54 0,66 n.a.
50 % 0,97 1,08 1,14 1,14
75 % 6,02 1,97 1,82 1,75
43
100% shade (theoretically), and LAI variable, but > 118. Average values close to
the Musa cultivars are given, yet the measurements vary within those groups.
3.3 Soils
Soil analyses were conducted twice in 2010. Once in April for the topmost 15 cm
layer of the fields, and once in December for the lower situated 15-30 cm beneath
the top layer. The April-testing-locations lay directly at the position, where the
Musa mother plants were later planted into. The December-testing-location thus
had to give way to A. the Musa cultivars that remained to harvest; B. the possibly
strongly influenced soil directly beneath the old rhizome. So, locations of samples
were replaced to 50cm from the original Musa planting location in diagonal
direction (i.e. between two root sampling locations). In a zigzag pattern across the
plot, 10 experimental plants were chosen, in whose vicinity the soil was analysed.
A large whole was dug, approx. 1 kg of soil scratched out of the vertical wall, and
bulked with the other 10 to gain one sample per plot.
The analyses were done by CATIE soil lab. The soil texture was evolved by
granulometric analysis with method of Bouyucos (Tab. 6). The experimental fields
are rather uniform in texture (few percentage points variation), although similarity
is greater for the topmost 15 cm. The minimal shade plot contains less sand and
partially more silt and clay. In the 15-30cm beneath, the silt content does not vary
> 2% amongst the shade levels; the 25% and 75% shade plots bear more sand
than clay. The texture is a ‘clayey silt‘ in the important topmost soil layer.
Tab. 6 Soil texture and its components in experimental fields. Four plots, two analyses; granulometric analysis
by Bouyucos in CATIE soil lab. Topmost 15cm tested in April 2010, beneath 15-30cm tested in December
2010. Average means for all four plots per layer tested.
Texture Minimal Shade 25% Shade 50% Shade 75% Shade
0-15 cm
15-30 cm
clayey silt 40% sand 27% silt 33% clay40% sand 27% silt 33% clay40% sand 27% silt 33% clay40% sand 27% silt 33% clay
clay 30% sand 25% silt 45% clay30% sand 25% silt 45% clay30% sand 25% silt 45% clay30% sand 25% silt 45% clay
44
18 Information (methods, replications, materials) in Erwid Valdiviaʻs Master thesis (unpublished).
Tab. 7 Soil analyses for certain parameters, in two analyses, by CATIE soil laboratory. Topmost depth tested in
April, lower 15cm to 30cm tested in December. In italics: organic matter (December-analysis), underlined:
organic carbon (April-analysis).
Shade pH H2O
acidity [cmol(+) l-1]
Ca[cmol(+) l-1]
Mg[cmol(+) l-1]
K[cmol(+) l-1]
P[mg l-1]
N [%]
C [%]
O.C./O.M.[%]
0-15 cm
Min. 4,63 3,74 3,00 0,91 0,39 31,6 n.a. n.a. 2,830-15 cm
25 % 4,61 2,53 3,67 0,96 0,51 36,5 n.a. n.a. 3,31
0-15 cm
50 % 4,68 2,42 3,79 1,03 0,46 41,5 n.a. n.a. 3,24
0-15 cm
75 % 4,57 3,21 3,50 0,90 0,58 61,7 n.a. n.a. 3,21
15-30 cm
Min. 4,68 5,09 2,34 0,58 0,26 10,1 0,15 1,70 2,9315-30 cm
25 % 4,69 4,65 2,23 0,60 0,37 8,0 0,16 1,87 3,22
15-30 cm
50 % 4,69 4,41 2,85 0,65 0,40 11,8 0,18 2,03 3,50
15-30 cm
75 % 4,70 3,92 3,24 0,80 0,32 8,9 0,17 1,91 3,29
The soil properties considered worth an analysis were chosen differently for April-
and December-analyses (Tab. 7). The topmost layer (April) was analysed for
organic carbon content and micro-nutrients19; whereas the beneath 15-30 cm
(December) were evolved for organic matter and total percentage of nitrogen and
carbon. Anyway, the methods are the same: determination of phosphorus and
potassium by extraction in solution ‘Olsen Modificado‘ pH 8,5; determination of
calcium, magnesium and exchangeable acidity by extraction in potassium chlorate
1N; pH in water; and finally carbon and nitrogen in combustion. The soil of our
experimental fields is strongly acidic, in low pH values of 4,57 to 4,7. Nutrient
Tab. 8 Soil humidity (by TDR) in four shade level plots, measurements located next to experimental Musa spp.
plants. TDR = soil humidity [%], N = 3. Data kindly made available by Erwid Valdivia.
Gros Michel Curraré Morado Pelipita
TDR [%] Minimal 37,37 38,75 38,05 38,02
25 % 42,05 40,86 38,94 38,32
50 % 39,27 42,65 42,89 41,50
75 % 40,51 38,38 40,76 42,24
45
19 The mirconutrient results (Cu, Zn, Mn, Fe) for 0-15 cm layer in the Annex.
contents are naturally lower in the 15-30 cm layer, than in topmost soil, e.g.
calcium, and particularly phosphorus are low. Calcium levels are moderate.
Phosphorus amounts in the topsoil are exceedingly high; especially for 75%
natural shading level. Organic matter contents (OM) are around 2,9 - 3,5 %, which
is at least sufficiently high. Most peculiar, the highest values are 3,5% (OM) and
3,31% (organic carbon content), to be found in 50% shade and 25% shade,
respectively; and for neither 75% natural shade has top values.
The soil moisture measurements were kindly made available by Erwid Valdivia
(Tab. 8). The data were collected by the time domain reflectometry method (TDR)20 and close to experimental Musa plants by using a portable sensor. Variation
within the shade levels is small (not shown), and the variation amongst the natural
shade levels are rather small as well.
And the soils of Costa Rica, especially in the Central Valley, are often of volcanic
(ashes) origin (amongst others, see Siles et al., 2010); and often, coffee is grown
on such sites.
46
20 Information (methods, replications, materials) in Erwid Valdiviaʻs Master thesis (unpublished).
4. Materials and methods
4.1 Data collection
The outline of the experiment and the fields were set up and designed before I
took up root studies in this project (see Chapter 3.2). The data were collected in
2,5 months, the beginning of September to midst of November 2010.
Preceding the root sampling, the experimental Musa spp. plants were measured
for their certain plant parameters21, to make the above-ground plant development
accessible alongside root development. At most one day after measuring, the root
sampling took place. The photosynthesis study of Erwid Valdivia was attuned to
root studies, so that the ‘harvest‘ of the experimental plants to assess their shoot
biomass followed root studies by few days. This schedule had to be changed for
individual cultivars, meaning that the chopping was realised before root sampling.
Given that the Musa spp. roots stayed fresh and vivid for days within the soil, it
should not have influenced the results. Thus, each cultivar was realised from root
sampling to analysis before the next one was begun. The litter layer was removed
before sampling.
Fig. 7 Root sampling methods, realised A. by auger (small samples) and B. by monoliths (large samples). A. =
auger collects a soil core in the metal tube (within the soil in the picture), and is handled by a metal grip (cut
by the upper edge of the picture). B. = metal frame marking the sample; additional (not shown): spade, mallet.
47
21 See Chapter 3.2 for method description and data.
A. B.
In root sampling two soil coring methods were used. Large (monolith) and small
(auger) samples were taken for three plants per level of shade. A standard auger
for soil sampling was used to represent a small-sample-method (Fig. 7 A.). It is
drilled by sheer man force into the ground. Soil accumulates within a slender metal
tube at the bottom of the central metal bar. After removing the auger out of the
ground, the remaining soil is forced out of the auger, collected in a good bucket,
packed into a small plastic bag, ‘airtight‘ closed, labelled correctly and stored in an
(un-)cooled but shaded place. A large-sample-method forming monoliths
demanded three tools (Fig. 7 B.): a metal frame, a spade (or good shovel), and a
thick (rubber) mallet. The frame is placed onto the ground, marking the sampling
location, and dug into the ground using the mallet. The soil forming the sample is
dug out with the spade into any kind of large bucket or nylon sack. It is labelled,
the sacks closed and kept in shade.
Supporting utilities are folding rules and permanent markers (labelling). The
measures of the samples had to be controlled during sampling, as to which depth
the monolith is excavated, and to which depth the auger is drilled into the soil, to
ensure a correct volume of soil removed. It was more difficult for the monolith, due
to the square-shaped, hugh surface area, which was laid upon uneven and oblique
ground. At the auger, the inner height of the metal tube was marked at the desired
height before sampling begin.
Implement a useful system of samples located around a Musa spp. experimental
plant was rather complicated. Referring to the radial, shallow, and horizontally
extended root system of bananas (Blomme, 2000a; et al., 2000b), the positions for
sampling were laid out equally distributed around the plants (Fig. 8). In monolith
(large samples) method, one sample was replicated four times around one plant,
being 30 x 30cm surface and 20cm deep. The sample began at 40cm distance
(horizontal) from the mother plant. In auger (small samples) method, the small
sample was taken at 20 locations around a plant, of equal size and shape, and the
five positions of samples in one direction were replicated for the other directions.
Thus, three distances (horizontal - 40cm, 80cm, 120cm) and two depths (vertical -
0-10cm and 10-20cm) were realised. In this auger method, every sample may be
48
uniquely defined by its ‘location parameter‘, i.e. direction - distance - depth. In
monolith method, the ‘location parameter‘ is restricted to direction from the mother
plant. The ‘direction‘ was chosen (see Fig. 6, p. 37, Chapter 3.2) to study whether
the close coffee rows had any effect upon Musa root formation, as two directions
of samples were located between coffee row and banana, and two directions in
the middle of the inter-row. Per level of shade, three experimental plants per
cultivar were used to form three replications. Auger method was only applied for
cultivar dessert banana AAA ‘Gros Michel‘.
Fig. 8 Design of A. auger (small) sampling method, only AAA ‘Gros Michel‘; and B. monolith (large) sampling
method (four Musa cultivars).
49
A.
B.
The basic information on our sampling methods are to be found in Tab. 9.
Collected samples were removed from the field in their initial soil status to the
washing area, in our case the CATIE laboratory facilities. Storing samples as
whole soil bulks requires space but gains time, as the roots stay remarkably fresh
within it. Small samples were capable of being stored in a common fridge. The
flaw of the now emerging analysis chain is that samples had to be stored between
the singular steps of work, which demanded time for packing and unpacking,
labelling, required storing capacities and materials, and finally caused a slight
drying out of roots in the fridge for the first cycles of samples. Later we could
eradicate that weakness.
Sample by sample was washed through a standardised sieve of 2 mm wire
diameter separating roots from other firm contents and soil particles, supported by
hand and water pressure. Finer sieves do exist, but this was a concession to the
strictly limited time frame. The remaining firm contents were put in a transparent
bowl full of clear water. With tweezers the desired roots were extracted and
separated into two groups. All other solid leftovers, like litter, stones, branches
were disposed. Roots were separated into Musa roots and all other roots
available, containing those of shade trees, coffee and sporadic smaller herbs.
Considering the size of the sieve used and the duration of a total-separation to
Tab. 9 Basic information of monolith (large) and auger (small) sample method.
auger technique monolith technique
no. samples per plant 20 4
replications per shade level 3 3
no. samples per cultivar 240 48
time required 4 plants in 8 hours 8-12 plants in 8 hours
persons working 2 1 (-2)
soil volume 567,5 cm3 18.000 cm3
depth from soil surface up to 20 cm up to 20 cm
surface on soil ground 56,75 cm2 900 cm2
cultivars sampled 1 (240 samples) 4 (192 samples)
50
every single finest root, with possibly a demand for binoculars, it was decided to
leave out roots < 1 mm diameter. The crux of the matter is that there is no option
to measure the roots precise diameter. Therefor, separating had to be done by
sense of proportion, which had to be learned and trained. Yet, a possible error of
roots left out unseen exists.
Musa spp. roots are easy to distinguish from Erythrina poeppigiana and Coffea
arabica roots. Changing in colour from black over grey to flawless white -
depending on the cultivar, age and phenological status -, they differ considerably
from ochre brown coffee and tree roots. Second, they are flexible and easy to fold,
especially smaller roots; and finally, they consist of very watery and easy-to-
pressurise material. If pressed in by a tweezer, the tweezer drills into the root
immediately and the root gives a little noise like a squeeze. The coffee and tree
roots however are very hard and not capable of being pressed in.
Finally both root parts of each sample were analysed. A lab computer hosts the
programme ‘WinRHIZO (Pro) 3.9 2004‘ by Regent Instruments, working with an
optical scanner by image acquisition, a Large Area scanner, though the images
used were smaller. The roots of a sample were placed in flat, transparent bowls
filled in clear water that should cover all roots. The scanner generates an image,
which is analysed due to previously given settings. The programme displays the
determined roots diameter for each small section of a root and sorting the
furthermore gained values into categories defined for root diameters (see Chapter
4.2). Both parts of a sample, Musa and other roots, were scanned separately.
Some samples had to be divided into multiple parts, when the root content
transcended the bowls capacities.
We weighed the separate root contents, if possible, directly after scanning. Roots
were dried carefully using a coffee filter paper. Two scales were used
simultaneously to speed working up, both featuring a preciseness of 0,0002 g.
Each portion of roots then was packed in a small paper bag, labelled and put into
an oven. The samples were dried at ca. 75-80 °C for usually three to four days.
Whilst these days a certain number of samples was monitored for weight changes
51
every day, to find the first possible day to start dry weighing when changes would
be marginal. Roots were disposed after that last step.
The data were collected by myself and several further persons involved. Erwid
Valdivia, Dr. Oscar Bustamante and Cindy, who is Bioversity‘s phytopathological
lab assistant in CATIE, helped to deal with the hugh volume of work. Two local
field worker were employed, one of them working independently in the end.
Several lab workers helped analysing roots, whereof two were employed
continuously. All different steps of work had to be learned and trained, which made
a continuous team necessary to gain qualitative results.
4.2 Data analysis
The scanning programme, WinRHIZO (see above), released its data in classic .txt
files, which were implemented into a spreadsheet programme. Several
transforming errors occurred during this implementation, that had to be erased.
Many samples, the monolith (large samples) in particular, had to be divided into
several parts to allow proceeding (scanning and weighing); those were summed
up again. In cultivar AAA ‘Gros Michel‘, the auger (small) samples were taken at
the equal 40cm-distance-location like monoliths; thus, the contents of auger
samples had to be added to the monolith samples. In the end, each sample can be
defined uniquely by its determination parameters, which are cultivar, plant number,
replication; level of shade, direction from plant; and for auger additionally distance
(horizontal), depth (vertical); and the parts of each sample were taken separately:
Musa roots, and coffee and tree roots.
Some calculations have been introduced, before the database was ready to be
used for analyses in Chapters 5-7. The scanning programme listed the important
root variables for every diameter class we introduced beforehand. These were
summed up partially for all diameter classes above 1 mm and used for further
analyses. The diameter classes implemented were <0,5 mm; -0,7 mm; -1 mm; -1,5
mm; -2 mm; -2,5 mm; -5 mm; -7,5 mm; -10 mm; >10 mm. The most important root
52
variables were root length [cm], surface area [cm2], project area [cm2] and volume
[cm3]. Additional root variables were calculated. Within literature, roots frequently
are defined in the following ways: root length density [cm cm-3], specific root length
[cm g-1] and biomass per unit of soil [g dm-3]. For the latter computed variables, the
dry biomass [g], determined by weighing, and the samples‘ volume, i.e. 567,5 cm3
(auger) and 18.000 cm3 (monolith), were required.
In the scanned results, the diameter classes > 1mm could be chosen easily for
calculations, as all diameter classes are displayed separately. Yet scanning
showed that several fine roots < 1mm frequently remained after visual judgement
during separating, a concern that was expressed above. These ‘fine root residues‘
are of more importance to root length than weight. For weighed results, there was
no possibility to exclude those residues before weighing; thus, their importance is,
though included in weighed results, considered of minor importance to biomass
results.
An adjustment was implemented for the small number of very coarse tree or coffee
roots, almost thick as trunks, that were found in sampling locations. In about ten
samples, such roots did not fit into the scanner, due to being to thick to close the
lid. The roots were cut horizontally in two halves and scanned. Consequentially the
results have to be readjust to match the normal results. Some ‘tryout-roots‘ and its
halves were studied thoroughly, its insights transformed into a simple system (Tab.
10). Depending on whether both halves were scanned at once (in the same bowl)
Tab. 10 System implemented to correct scanning results of coarse tree/ coffee roots to match normal root
results. The first column describes whether all roots lay within one transparent bowl to be scanned or within
two, whereof all „upper“ halves lay in one, and all „lower“ halves lay in the other. RLD = root length density,
SRL = specific root length. In italics: result approximating realistic values. (biomass per unit of soil does not
depend upon scanning results)
Half roots in:
Length Surface area Project area Volume RLD; SRL
2 bowls arithmetic mean of both
add both choose higher result
add both calculation normal
1 bowl half of result the result half of result the result calculation normal
53
or in two steps (separate bowls), the results had to be changed. E.g. the volume
always matched perfectly, whether the whole root was scanned, or both its halves
were scanned and added. On the other hand, for project area, the scanner
apparently measures the broadest part of the tube-shaped root, and the length to
then compute the projected area; thus, if two halves are measured in the same
bowl, the arithmetic half of the total project area will represent a idealised root, not
the real distribution of width. The surface area then is extended for the cutting area
at both halves; it is not accessible how the programme estimates the root, as a
tube or cut half, and therefor the result may be imprecise.
The database is formed out of the all those calculations, and forms the fundament
of further analyses. A couple of invalid samples appeared from time to time.
Sampling could not be completed, due to stones within the ground, or an error
during root analyses occurred. Such values were excluded.
The analyses then were conducted in SPSS (PASW) 18 by IBM. Multivariate
analyses in General Linear Models were used; graphs developed and descriptive
statistics applied (order and analyse data for standard errors, means, etc.; more
information in Chapter 6.1). Correlation analysis, linear regressions and further
equations describing data distributions were calculated by a common table
calculation programme, Numbers ’09 by Apple (more information in Chapter 5.2
and 7.1).
54
5. Comparison of sampling techniques
Banana and plantain grown in field conditions promote a disadvantageous
situation to study their root traits (Blomme, 2000a). Certainly, any in vitro
experiment may not reassemble insights in ‘realistic‘ growing conditions equally,
but the minor accessibility of roots reduces the use of in vivo experiments (Draye,
2002). The major perspective may be to continue field studying in on-farm
conditions of smallholder farmers. Given that, soil coring was chosen to be tested
for its usability. The small size of samples was sub-optimal for spatially variable
tree root systems (Akinnifesi et al., 2004) and the (statistical) variability of results
high (Noordwijk et al., 2004). The method was applied to bananas before (see
Blomme, 2000a; et al., 2000b; Mukasa et al., 2005). Sampling must be efficient
and effective to be of use.
According to Hypothesis 4, the practicability is advantageous in small samples
(auger) in dense planting systems, whereas the suitability to specific
characteristics of banana root systems are better given for large samples
(monoliths), (Chapter 5.1). The statistical analyses are expected to show less
variability in monoliths than auger samples (Chapter 5.2).
In course of the statistical analysis, optimal intensities for sampling with either
method (monolith or auger) shall be suggested.
5.1 Comparison of methods
Monolith and auger samples shall be compared for their advantages in field
practicability (5.1.1) and lab analysis (5.1.2).
55
5.1.1 Field work & project embedment
Data collection methods oscillated between two needs; predictability for planning
on the one hand, and possible customisation during work on the other hand.
The acquisition of an root auger is rather long-term, as it is a scientific tool and
must be bought at an adequate enterprise or be lent from an research institute.
Shipping tools around the world, is costly, as is the acquisition of such a tool. The
tools used for creating monoliths, are far easier accessed. Rubber mallets and
spades are bought at ordinary hardware shops. The frame may be manufactured
by a local workshop out of simple metal bars. That may be cheaper and faster,
particularly in developing countries.
Labour costs formed a major part of our studies‘ expenses. Auger samples
required more time and worker per sampled unit, i.e. Musa plant or shade level,
because A. it is exhausting and a laboured process; and B. many more small
samples must be taken per unit, than large samples (Chapter 5.2). That aspect
refers to project planning as well; the work step of data collection was very
extended and reduced the amount of partial studies we were able to conduct.
Monoliths are comfortable to take (and of one person at a time22).
The auger, despite its costs and purpose, required modifications. A footboard was
welted to the central metal bar above the metal tube (Fig. 7, p. 43), because shear
arm force was not enough to drill it into the soil. It broke about three quarter
through sampling right above the metal bar, apparently not withstanding the
required force. The metal frame broke at the welds several times. A breakdown of
sampling tools during field work, especially if no workshop is immediately
available, is a weakness of both methods.
Customisation of soil cores involves their design, i.e. volume and sampling depth,
and their general geometric form. Augers are common-sized and not flexible in
56
22 Chapter 4.1, p. 46, Tab. 9
volume or form. Metal frames are designed for the purpose particularly, thus form
and surface area may be chosen. The depth may be freely chosen, as long as
spades may access the deep-layered soil - a problem of rather slender but deep
samples. The hole walls should not break in, it would manipulate the sample. The
metal tube of the auger restricts one sample in height. The footboard then
prohibited penetration into the soil for more than 30cm, because the horizontal bar
was wider than the metal tube‘s outer diameter. Whether deliberate or not, much
smaller a footboard would not be practicable for sampling. Restrained depth
access surely influences Musa spp. marginal, as to the superficial and shallow root
mat; it is something else for tree roots and their depth extent in these planting
systems (Noordwijk et al., 2004; Akinnifesi et al., 2004).
Space is, above- and below-ground, a restraining factor in such dense
agroecosystems, for mobility during data collection. Coffee shrubs disturbed
implementing the two methods particularly, considered the coffee is commercially
used and must remain undamaged. Above-ground vicinity restricts the auger
more, given that it must be held strictly vertical and turned during drilling. Hence,
strong superficial tree roots collided with the footboard. Below-ground vicinity has
coarsest tree and coffee roots 23 equally, which are not sliceable by auger and
hardly by spade, and stones. We used knives and thin metal bars. In small
samples, the hole‘s walls must be maintained, though difficult in the limited space;
and the auger has to be removed and replaced precisely without dropping the yet
gripped soil and without manipulating the sample. Stone interruptions almost
prohibited taking samples, depending on the stone size. The minimal shade level
turned out to be a challenge to sample it by auger method, i.e. completing a plant
took nearly an hour more than in the other plots, caused by its high stone content.
Stones were a major cause for invalid sampling.
57
23 The question is, whether the removal and analysis of that coarse, thick tree roots was necessary or not. Their presence may be of rather mechanical impedance to Musa roots, than of ʻcompetitionʻ in the sense of nutrient uptake, than they are of structural purpose. Despite quantifying the mechanical impedance, the data analyses are delicately changed by adding those trunks, what may not be of use to assess distribution and competition anyway. And still, as being within-sample, they belonged to root biomass gathered by coring.
Monoliths engross a large part of ground surface, i.e. 900 cm2. The large square
hardly is suitable into the limited space by coffee plants, tree trunks and superficial
thick roots. That problem occurred in 75% natural shading particularly. Dislocating
samples may change root trait measurements delicately, as the spatial variability is
assumed to vary considerably. The small circle of auger method, i.e. 56,75 cm2,
matches open space easier. But variation due to root proliferation should impact
even a small dislocation stronger, as the sampling position was separately tested.
The hugh soil volume of monoliths was a lot to deal with, in transport and storage;
auger samples were more comfortable. Root studies are a matter of facilities
always.
5.1.2 Lab work & results
Quality and direction of the study begin in the field. The purpose of the auger
method was to assess root traits in their proliferation around singular Musa plants;
whereas the purpose of monoliths was to create a simple pattern to gain solid
biomass amounts. Thus, the ‘positioning‘ of a sample may only be defined for
auger samples by distance (horizontal), depth (vertical) and direction. A finer
proliferation study is not possible, as in both methods the samples are ‘bulked‘ and
Fig. 9 Disturbances affecting the soil volume excavated, in A. auger (small sample) and B. monolith (large
sample) method. A. = soil in metal tube is compromised and thus of lower surface level than outside; B. =
uneven or descending soil surface unmatched by ‘rigid‘ sample shape.
58
A.B.
no root growing direction may be distinguished. The number and positioning of
samples determines the usability of results and the objects studied. A system
concentrated upon the Musa in its centre may not gather more information about
the adjacent plants (coffee, trees) than their relative roots within the samples.
A high heterogeneity in edaphic components is anticipated, particularly for high
natural shade levels. Logically, the small samples are expected to depict the
divergences in site conditions, whereas the large samples rather are supposed to
show a more homogenous picture of the site. Consequentially, the small samples
(auger) may be too variable to provide insight into a whole plot; or they might
depict an individual Musa‘s root system more realistic, than monoliths.
Whilst drilling the auger into the ground, the soil bulk pushes upwards within the
metal tube. During that process, the soil bulk is compressed, maybe by any kind of
friction force (Fig. 9 A.). Thus, the bulk height is lower than the ground surface and
possibly the bulk density of the soil core increased. We measured the inner length
of the metal tube, but the outer may be preciser as not compressed. Monoliths
Fig. 10 Scanner acquired images of: small samples (auger, no. 168): AAA ‘Gros Michel‘, A. = banana roots,
and B. = tree + coffee roots; and of large samples (monoliths, no. 516): AAA ‘Morado‘, C. = banana roots, and
D. = tree + coffee roots, two out of three images.
59
D. C.
B. A.
have that large surface area, and placed upon uneven or descending ground the
removal of the correct soil volume is equally difficult. The volume of soil taken is
important, as the root contents are always related to the certain amount of site soil
they occur from, otherwise the determination is incorrect.
Influencing the volume were stones as well. They were removed and in no kind
counted or measured, so that their impact is not detectable. Anyway, stones are a
usual edaphic component and restrict root growth of any plant. Replacing
samples, whether due to stones, tree roots or coffee shrubs, took place (Chapter
5.1.1). The shift to enable samples, that otherwise would be prohibited, ‘optimises‘
the Musa root system, but it is no longer truly realistic: the thick root is not
gathered as a mechanical impedance, and the Musa root deficiency in that part
not assessed.
Soil cores have to suit the specific Musa root system. Strong lateral shoots for
vegetative reproduction emerge from the mother plant‘s corm (Fig. 11 A.). At their
position at the corm, no root axes emerge, and the soil volume unoccupied thus by
roots increases like a funnel. Small samples (auger) placed in that space will
gather no Musa roots. That may be realistic, but it leaves no biomass to be
analysed. Monoliths usually get the next root axes by their large size and square
Fig. 11 Musa spp. root system, A. = view from above upon cut pseudostem, root axes, laterals and sucker
(white, thick, at right/ left side). B. = two sucker emerging proximal to mother plant pseudostem, after approx.
6 months growth; C. = poorly cut root axis remaining in sampling location of auger.
60
A.
B.
C.
form. The sharp edge of the auger often slipped along root axes instead of cutting
them neatly (Fig. 11 C.), until they rip and actually within-sample roots remain.
Superficial root axes slightly crossing the location often were pushed aside and
also were deficient in the removed soil.
Data analyses in the lab are influenced by the biomass amount gathered by large
or small samples, although the procedure is equal. Commonly, larger samples are
less convenient for lab analyses than smaller samples (Fig. 10). Balances are
more difficult and time-consuming in equilibration, ovens require more time, and
even parted samples are very crowded in scanner bowls (Fig. 10 D.), with many
crossings. Double-scanned bowls had diverging results in image analysis, though
the equal root amount was scanned. Whereas singular roots were very conform in
separate scanning processes. Larger samples started to dry in the fridge, but
small ones were well enough covered. On the contrary, small samples had so
marginal Musa root biomass from time to time, e.g. in the most distant sampling
position, that they hardly exceeded the accuracy of the balances (Chapter 4.1).
The two auger samples positioned at 40cm distance added, form 7,05% (minimal
Tab. 11 Musa root contents gathered in auger samples and monoliths, for four shade levels in the cultivar
AAA ‘Gros Michel‘. Average values per sample and standard errors (SE) are for N = 12 in monoliths (with 75%
shade having N = 10 due to invalid samples), and N = 12 in auger positions (with 40 -- 20 cm position having
N = 10 in Minimal, 50% and 75% shade). Musa roots are given in DB and RLD.
Shade augerShade auger DB [g] RLD [cm cm-3]DB [g] RLD [cm cm-3]
DB [g] RLD [cm cm-3]monolithsmonoliths
Minimal 40 -- 10
40 -- 20
25 % 40 -- 10
40 -- 20
50 % 40 -- 10
40 -- 20
75 % 40 -- 10
40 -- 20
0,065 ± 0,020 0,064 ± 0,0181,56 ± 0,63 0,023 ± 0,004
0,045 ± 0,016 0,039 ± 0,0101,56 ± 0,63 0,023 ± 0,004
0,107 ± 0,033 0,081 ± 0,0220,73 ± 0,11 0,018 ± 0,002
0,027 ± 0,012 0,024 ± 0,0070,73 ± 0,11 0,018 ± 0,002
0,054 ± 0,012 0,048 ± 0,0081,23 ± 0,30 0,024 ± 0,004
0,015 ± 0,005 0,032 ± 0,0131,23 ± 0,30 0,024 ± 0,004
0,070 ± 0,026 0,061 ± 0,0180,56 ± 0,117 0,011 ± 0,001
0,011 ± 0,005 0,021 ± 0,0090,56 ± 0,117 0,011 ± 0,001
61
shade), 18,36% (25% shade), 5,6% (50% shade) and 14,47% (75% shade) of the
respective monoliths‘ dry biomass (DB). That shows, that A. often the biomass
proportion in the two augers is close to the soil volume proportion (an auger has
3,15% of a monolith‘s soil volume); i.e. the double DB (6,3%); B. the DB in the
augers seems rather higher than the DB in monoliths (Tab. 13), which is logical:
the auger position is close to the Musa plant and shows a small share of the root
system, whereas the monolith spreads from 40 to 80 cm distance; we anticipate
the root density to decline with increasing distance (Chapter 6.1.2; Araya, 2005).
The flat, large monolith ‘balances‘ the changing DB, even better observable for
root length density (RLD). Concerning the latter, singular auger samples must be
compared, as it is a ‘standardised‘ unit per soil volume. Therefor, A. the 40/ 10cm
position has highest RLD, as the sample is closest (horizontal distance) and
topmost (vertical depth) and smallest (auger) to the Musa plant; B. the 40/ 20cm
position always has lower values, consequentially, as a. we anticipate the root
density to decline with increasing depth (Chapter 6.1.2; Araya, 2005); and b. DB
develops similarly (Tab. 11); and C. the monolith RLD is lowest, due to the same
reason as DB (above).
The total root contents gathered within the samples of both methods (Musa [only
around ‘Gros Michel‘ plants] and ‘other‘, i.e. Erythrina poeppigiana and Coffea
arabica roots) are for RLD in monoliths 0,095 ± 0,017 cm cm-3 (average ± SE;
minimal shade); 0,065 ± 0,008 (25% shade); 0,064 ± 0,006 (50% shade); 0,048 ±
0,005 (75% shade). Correspondingly, the 40 cm (horizontal distance) and 10 cm
(vertical depth) position has RLD within auger samples 0,207 ± 0,244 cm cm-3
(minimal shade); 0,211 ± 0,276 (25% shade); 0,175 ± 0,021 (50% shade); 0,201 ±
0,023 (75% shade). Compared to Schaller et al. (2003a), who obtained approx.
2,5 - 2,7 cm cm-3 RLD in the topmost layer of Coffea arabica combined with
Eucalyptus deglupta, there seems to be less total root length in our plots. Possibly,
that is caused by the fine roots < 1 mm being left out, whereas (Schaller et al.,
2003a), primarily measured the roots < 2 mm only; yet, a different level of total
roots present may result from species combination, site characteristics etc. Turner
(2005) named possible RLD for only bananas to be 1 cm cm-3, or 4-50 cm cm-3,
which is much higher indeed. The total DB gained by monoliths forms 19,83 ± 4,40
62
g (average ± SE; minimal shade); 17,71 ± 4,48 (25% shade); 23,78 ± 5,59 (50%
shade); 23,05 ± 5,76 (75% shade). In both root length and biomass, thus, ‘other‘
roots form the major share of the total root amount in samples, though less for
RLD, and strongly in DB, causing the root contents to rise in 50% and 75% natural
shade. In those two, ‘other‘ roots form approx. > 18g of total DB. In the two 40cm
positioned auger samples added, the total DB gathered (and % of corresponding
monolith) is 2,27 g (average; 11,45%; minimal shade), 1,5 g (8,47% in 25%
shade); 1,41 g (5,93% in 50% shade), and 1,42 g (6,16% in 75% shade).
Fees to use the lab equipment are of course institute-specific, but in that case we
had to pay for each sample separately. Thus, the small samples were counted, no
matter how few biomass included; and large samples were divided into many
parts, thus counted individually. For small samples separation took less effort,
though it is easier learned with large samples for new staff, but there are many
additional particles. Large samples were more convenient in washing, in total.
5.1.3 Improvement
Improving core sampling methods, or deciding for a method for a root data
collection, is primarily a matter of the intended purpose. What kind of root
proliferation shall be assessed by the cores? It can be decided, A. is the spatial
arrangement of the growing system best suited by a sampling pattern over the
whole plot, or concentrated upon individual plants of an individual cultivar; or B.
what form and size of cores may be fitted in proper locations into the densely
planted agroecosystem. The parameters of coring methods are partially easier or
more difficult in modification.
The natural radial form of Musa root systems is best matched with a radially
spread set of cores, that are located at high root densities in the direct proximity
around the pseudostem, and thus, the rhizome (Fig. 12). In small samples (auger),
the distant 1,20 m position did provide few Musa biomass and is considered of
minor importance to representing a Musa root system, thus could be eradicated.
63
Then by A. taking samples in more directions, and B. adding new locations in
between, with equal number of directions (Fig. 12); more cores in the plant
proximity could be taken. The focus upon the vicinity of the rhizome could, as
presumed by us and Draye et al. (2005) and Araya (2005), reduce the variability in
cores, from plant-to-plant; and reduce the inflexibility towards sucker development,
without dismiss the ‘realistic‘ representation of individual Musa plant root
formation. Large samples (monoliths) may only be added as much as space
around the Musa plant within a first circle of monoliths enables to. Yet 6 or 8
monoliths would destroy the experimental plot severely and cause almost an entire
root mat excavation. The latter may be rather an improvement to effectivity, than
efficiency. The sample numbers and plant replications are the best-to-attend
parameter, which may be changed for a soil coring method (Draye et al., 2005;
Araya, 2005; Blomme, 2000a); next to their positioning. They may be important
tools to determine the quality of the results (Chapter 5.2); and simple positioning of
samples in densely planted mixed-species systems is the advantage of our auger
method.
Fig. 12 Improving soil coring methods, left: small (auger) samples, right: large (monoliths) samples. Left:
1,20m sampling position removed, additional 80cm/ 60° position (six directions), increase original 4 to 6
directions, and find auger with e.g. 16cm diameter of metal tube. Right: upper part is the original sample,
bottom is the new sample: reduce surface are to 10 x 40cm, thus increase width (perpendicular to line: Musa
- sample) to 40cm; and increase depth to 30cm.
64
The form of cores is often less changeable (Fig. 12). A circular form could be
better used, when the diameter could be larger; biomass contents would increase,
soil volume stays small, and the cutting interface increases. A square form is more
accommodating, at any rate soil volumes should be reduced. A shape, comfortably
to be dug out by spade is necessary. Considering the radial root formation and the
sucker-related trouble, the vertical plain facing the Musa plant must be the most
important one. It cuts roots closest to their arising point, hence it must be designed
particularly large and as deep as required. The longer that plain is, the more roots
may be cut, and thus the third dimension of the monolith could be small as the
spade (Fig. 12). In that ‘tangential layout‘ the large plain is perpendicular to the line
Musa plant - next sample. Customisation is the one hugh advantage of our
monoliths. Deeper, shorter (horizontal distance) and wider samples may increase
the output on roots, and hence better suit in a densely planted system, as it is
more shaped like a ‘profile wall‘; it has only 44% of the surface area, but still 66%
of the soil volume content. A soil bulk in size between both tested methods could
make lab analyses more convenient, by providing enough biomass to reduce
variability, but small enough to proceed it; and increase the practicability in the
dense fields.
Disturbances and their unquantified impact upon sample volumes have to be
eradicated as far as possible. A soil bulk could be weighed right after excavation.
Alternatively, the stones or tree roots above a certain size could be measured in
some way (volume or weight).
5.2 Statistical comparison
Monolith and auger samples are compared for the variability of results (5.2.1) and
consequentially, optimal sampling densities will be suggested (5.2.2).
65
5.2.1 Preciseness
The standard errors (SE) were calculated as the percentage of the average Musa
root content of a small sub-group of samples each. The dessert banana AAA ‘Gros
Michel‘ was solely studied, thus the very same 12 plants compared. The sub-
groups include all samples of one plant (monoliths; Fig. 13 A.), or each sampling
position per level of natural shade, including all three replication plants (auger; Fig.
13 B.), respectively. Given that standard errors differ strongly due to the measuring
scale of the root variable used (e.g. ‘volume‘ has very high values, compared to
‘root length density‘), that this standardisation allows to compare all five important
root variables chosen from the database. Thus, the groups are N = 4 for monolith,
with Plants No. 1; 5; 9 being minimal shading, 2; 6; 10 are 25% shading and so
forth. For auger, the groups are N = 1224.
Results
The % standard error/ mean (%SE/M) varies less among the root variables for
auger (Fig. 13 B.) than for monolith (Fig. 13 A.) method. For both, the ‘weighed‘
variables (fresh weight (FW) in monolith: max. 62,96 %SE/M; dry biomass per unit
of soil (DBU)) tend to higher SE than the ‘scanned‘ variables (e.g. root length
density (RLD) in monolith: min. 6,5 - 7,8 %SE/M). By ~ 10-60 %SE/M, monoliths
have less SE than auger samples, by ~ 30-80 %SE/M. For the important root
variable RLD, the difference amongst Musa plants may be max. 41,63 %SE/M
(monoliths) or the difference amongst sampling locations max. 47,04 %SE/M
(auger). Generally, 75% natural shading (in both methods) and minimal natural
shading (in monoliths) tend to show greatest variability amongst root variables (in
monoliths: plant 4; 8), and amongst plants or sample locations; and 75% and
minimal shade generally have higher %SE/M (auger), like the most distant
sampling locations from the plant (labelled ‘D‘, ‘E‘, e.g. 50% shade) show.
66
24 Invalid samples reduced N in 10-20 cm depth positions by 1-3, in Minimal, 25% and 75% shade.
Fig. 13 Percentage standard error of mean, cultivar AAA ‘Gros Michel‘ and sampled separately by both auger
(B.) and monolith (A.) method; for five root variables; standard error calculated for N = 4 (A., monolith) and N =
12 (B., auger); invalid samples possibly excluded. RLD = root length density, B.p.U.o.S. = biomass (dry) per
unit of soil. Plants 1, 5, 9 = minimal shade; 2, 6, 10 = 25% shade; 3, 7, 11 = 50% shade; 4, 8, 12 = 75%
shade. Labelling of auger method graph: letters for sampling locations, A = 40cm/ 10cm; B = 40cm/ 20cm; C =
80cm/ 10cm; D = 80cm/ 20cm; E = 120cm/ 10cm.
Discussion
Large samples (monoliths) indeed provide less %SE/M than small sized samples
(auger), thus confirming concerns expressed before (Noordwijk et al., 2004;
Draye, 2002), with 10-60 %SE/M in monoliths, and 30-80 %SE/M in auger. And
that even though sub-groups of monoliths included only 4, but sub-groups of auger
already 12 samples, and the magnitude of SE is likely to decrease with the
increasing numbers of samples involved. SE of that magnitude are almost
67
A.
B.
undesired, as they are to be found for auger. The further distant sampling locations
of Musa plants in auger method seem to have slightly increased %SE/M (~
60-80%); considered we obtained very few root biomass (Musa) in those
sometimes, that does not seem surprisingly odd (e.g. 80/ 20cm, and 120/ 10cm)25.
Thus unexpected, the variability amongst root variables seems higher for
monoliths than for auger samples. A divergence in ‘weighed‘ and ‘scanned‘ root
variables would be explainable (though low divergences occur), as the different
measurement equipment used could account for it; but in Musa plant 4 and 8
(monolith) a wide divergence amongst ‘scanned‘ variables is to be seen, e.g.
volume (Musa 4: difference is 58,41 %SE/M) or RLD (difference 10,63%). The two
plants are of 75% natural shading; and despite monolith results, the variability is
very low amongst ‘scanned‘ variables for Musa by auger in 75% shade (max.
difference 7,3%). ‘Weighed‘ variables though differ more for auger, than monolith
(e.g. 75% shade max. difference 32,6%). Maybe the large proportions of roots
gathered in monoliths had disadvantages in lab analyses, as roots crossed much
in scanner images and balances oscillate stronger in terms to find the weight.
A variability is thus observed in magnitude of SE and differences amongst root
variables more for high natural shade levels (plant 4, 8 and auger: 75% shade).
Carr (2009) observed, that the plant to plant variability increases under
competition or stress; and we anticipate a general stronger field heterogeneity in
high natural shading (75% shade), particularly in edaphic components and light
availability, by denser planted shade trees. Yet the very good results of minimal
shading (auger; monolith: plants 1, 5, 9) are surprising, as we had many difficulties
with stones to overcome during sampling. Two observations then should be done:
A. the dry biomass for Musa plant 1 has an unusual high %SE/M, and B. the 50%
shade of auger samples has higher differences amongst root variables; both
phenomena appear later on in root biomass analyses again. RLD provides
constantly lower SE, which affirms the decision to use it, next to frequent use in
literature. FW has highest SE, but differs seldom from DBU (e.g. 75% shade in
68
25 Chapter 5.1.2
auger) and lower %SE/M in monoliths; thus, the first dried samples in the fridge
may not have been influencing. DBU does vary from the development of other root
variables (e.g. Musa 1 monolith: 62,49 %SE/M), but due to its relating dry biomass
to a soil amount, it should be used.
5.2.2 Sampling intensity
Inquired was, in which intensity samples of either size had to be laid across the
plots to enable effective but efficient analysis of roots. The practicability of
sampling methods is restrained, which prohibits to take a great number of
samples. The best intersection of lowest % standard error/ mean (%SE/M) and
fewest amount of samples is sought.
Basic sub-groups are N = 4 (one Musa plant) in monolith, and N = 5 (one direction
of one Musa plant) in auger sampling method. Thus, not each sampling location as
in the prior Chapter was taken as a basic unit, but one ‘set‘ of all sampling
locations. The dessert banana AAA ‘Gros Michel‘ was studied, and the root
variable root length density (RLD). The %SE/M was calculated for increasing sub-
groups, i.e. per level of shade, which is 4 - 8 - 12 samples for monoliths (Fig. 14
A.), and 5 - 10 - ... - 55 - 60 samples for auger (Fig. 14 B.). Higher amounts of
samples were given by choosing one plant per shade level (basic), i.e. 16 - 32 - 48
for monoliths (Fig. 14 A.), and 80 - 160 - 240 for auger (Fig. 14 C.). Thus, the sub-
groups except those including all samples available, may be formed out of many
combinations of Musa replications and direction-sets per shade level. Exemplary,
each 12 combinations of possible basic sub-groups were used to create an
average %SE/M for 25 or 40 auger samples or 16 monoliths. Which ones used,
and how many, was arbitrary chosen. The resulting relation of sample amount
(independent variable) and %SE/M was found best describable by power
functions, of the form:
with y = %SE/M; b = sample amount.
69
Fig. 14 Sampling intensity for A. monoliths, both per-shade-level (≤ 12 samples) and all-shade-levels (≤ 48
samples); B. auger samples, per-shade-level (≤ 60 samples); C. auger samples, all-shade-levels (≤ 240
samples). %SE/M over amounts of samples; for root variable RLD. For dessert banana AAA ‘Gros Michel‘.
Invalid samples excluded, thus not always the full sample amount is reached (e.g. B., 60 samples). Power
functions of type Y = c * bx describe the results well.
70
A.
B.
C.
Then, several chosen ‘idealistic‘ values of sample amounts or %SE/M could be
tested for their usefulness (Tab. 12). 5 to 10 %SE/M would be desirable, but were
thought to be still achievable by auger and monolith sampling method; and adding
samples to the yet taken ones per Musa plant, would allow max. 28 auger samples
and 8 monoliths, before field space and lab analysis duration limit the extent.
Results
The %SE/M is higher for auger (38-52%) than monoliths (16-28%) for the basic
sub-group (Fig. 14). In both methods, the %SE/M decreases for RLD with
increasing amount of samples (Fig. 14), except 50% shade in monolith (Fig. 14 A.;
Tab. 12). Including all shade levels, auger samples reach 7,6 %SE/M for 230
samples (i.e. 10 invalid samples) and monoliths 8,82 % for 46 samples (i.e. 2
invalid; Fig. 14); thus, a decline below 10 %SE/M was achieved with our full
sampling extent. Minimal shading has higher %SE/M than others (Fig. 14 A./ B.),
and is comparable to 75% shade in auger, but not in monoliths.
Tab. 12 Optimal sampling intensities tested for dessert banana AAA ‘Gros Michel‘, for both methods auger and
monolith. Amount of samples required for 10% SE/M per level of shade/ all shade levels (1.) and for 5% SE/M
(2.); %SE/M achieved by 28 samples per Musa plant in auger or 8 in monolith (3.), and by 84 samples per
level of shade in auger or 24 in monolith/ or 336 in auger per level of shade, and 96 in monolith (4.). For root
variable RLD, and described by power functions of type Y = c * bx.
Method Shade [%SE/M]1
result [%SE/M]2
result [amount samples]
3
result [amount samples]
4
result
Auger Min 10 201,9 5 967,8 28 23,96 84 14,74
25 % 10 131,7 5 674,6 28 19,29 84 12,10
50 % 10 78,1 5 311,0 28 16,73 84 9,64
75 % 10 228,3 5 1151,6 28 24,56 84 15,34
All 10 131,4 5 533,8 336 6,29
Monolith Min. 10 37,1 5 158,0 8 20,82 24 12,31
25 % 10 18,6 5 77,2 8 15,05 24 8,82
50 % 10 35,5 x104 5 59,59 x1012 8 14,79 24 14,21
75 % 10 42,5 5 693,5 8 15,13 24 11,52
All 10 36,7 5 152,6 96 6,26
71
In the calculations of ‘idealistic‘ values, the 5 and 10 %SE/M require sampling
amounts (Tab. 12) for separate shade levels, which are far higher than the max.
amounts taken by us, e.g. those were 60 in auger, and 12 in monoliths. For all-
shade-levels, the ~131 samples (auger) and ~37 samples (monoliths) for 10 %SE/
M are below the max. amounts (240 for auger, 48 for monoliths) taken by us. At
any rate, from 10 to 5 %SE/M a sharp and high increase in sample amounts
required takes place, that indicates a low reduction of SE/M, but a high increase in
sample numbers. One Musa plant studied with 28 (auger) or 8 samples (monolith)
would achieve at least 16,7 or 14,8 %SE/M, respectively (Tab. 12). Extended onto
three Musa plants (i.e. 84 auger s. and 24 monoliths per shade level), %SE/M <
15 are achieved, which is only few percentage points lower than for three plants at
our max. sample amount (which is 11-18% for 12 monoliths as well as 60 auger
samples; Fig. 14 A./ B.). A decrease from 7-9 %SE/M (our max. sample numbers)
to <6,3% in the new max. sample number takes place (336 auger s. and 96
monoliths; Tab. 12).
Discussion
The development of %SE/M (root variable: RLD) over changing numbers of
samples shows indeed (Fig. 14), that the standard errors (SE) of larger sub-groups
decrease, compared to smaller sub-groups. The auger and monolith sample
methods approximate each other for larger sub-groups. Hence, the more samples
are taken with each method, the less divergence in %SE/M between both methods
exist. That is interesting, as the same banana plants were studied by both
methods. The maximum total sample amounts taken (i.e. 230 auger samples, 46
monoliths) achieve <10 %SE/M, which is a satisfying result for both methods;
considered, that the variability in small sub-groups was rather high (Chapter 5.2.1).
The maximum sample amounts taken per unit studied (i.e. per shade level: ~60
auger samples, ~12 monoliths), have 11-18 %SE/M.
The maximum sample amounts we used appear very appropriate in this case of
%SE/M development. The ‘intermediary‘ sample numbers (~60, and ~12) improve
compared to the ‘basic‘ sample numbers (5, and 4) by a difference of 5-10 %SE/M
72
(auger; Fig. 14 B.), or 27-34% (monoliths; Fig. 14 A.). Even a fully sampled plant
(20 auger samples) improves compared to the ‘basic‘ sample number with a
difference of 9-13 %SE/M. The ‘high‘ sample numbers (230, and 46) were tested
for replacement by ‘idealistic‘ sample numbers (Tab. 12; 336 auger s. and 96
monoliths), and that would improve the %SE/M by 1-3, but would be accompanied
by strong increases in sample numbers (Tab. 12; and see below). That does not
compensate the additional work effort. Given all that, an optimal sampling density
must not have less than 40-50 auger samples or 10 monoliths per-shade-level;
and optimal values suggested could be 80-100 auger samples and 16-20
monoliths per-shade-level. Consequentially, the number of replications per shade
level would increase by 1-2 AAA ‘Gros Michel‘ plants. In the case, that the
improvement suggestions to the auger sampling pattern in Chapter 5.1.3 are
realised, a slightly reduced number of samples per plant would evolve. It could be
considered to introduce instead a higher number of replication plants. That
possibly would reduce the variability (%SE/M) of the whole studied unit further;
whereas a plant as a basic sub-group would possibly be less precise. Thus, the
decision must be made with respect to the intended purpose, A. represent an
experimental plot of heterogeneous nature; or B. study individual plants in their
root distribution.
The power functions, which we used to describe the %SE/M development, indicate
the following: those functions experience a strong decline for the first additional
samples to the basic-groups, but become rather ‘flat‘ soon (Fig. 14). Thus, the
‘additional decline‘ in %SE/M is very low, when already large sub-groups are
further expanded. Given that, A. the ‘optimal densities‘ promoted in the
calculations by us, were too ‘idealistic‘ to be realistic (Tab. 12); B. for separate
shade levels, the divergences amongst the calculated required sample amounts
are rather low for 10 %SE/M, but increase considerably for 5 %SE/M. For the
latter, they become far more heterogeneous than the visualised development of
%SE/M in Fig. 14 would imply. The calculated sample amounts (per-shade-level)
exceed 78-228 auger samples or 37-42 monoliths for 10 %SE/M, and even
311-1152 auger samples for 5 %SE/M. The sample numbers of 10 %SE/M are
almost below those taken by us. But those of 5 %SE/M exceed ours by far, and
73
indicate by that: the results may be qualitatively improved, the more samples per
studied unit are taken; but those sample numbers are neither in space around
Musa plants, nor in any time available for field studies realisable. Thus, the
qualitative improvement is only realisable to a very certain extent. Given all that,
the involvement of power functions implies, that low SE of basic sub-groups and
low variabilities amongst individual samples is the most important aspect.
In the end, more samples in each studied unit (e.g. shade levels) have to be taken,
when a small coring method (auger) is involved, as if a large coring method
(monoliths) is used. One monolith must be compensated by more than one auger
sample, to ensure preciser results. That conclusion is quite conform to Draye
(2002) and Noordwijk et al. (2004), who express the demand for a considerable
soil volume to be analysed to balance the spatial variability and the edaphic
heterogeneity of sites. And the divergences amongst shade levels (compare
Chapter 5.2.1) are visible in Fig. 14 B. (monoliths), or in Tab. 12 (50% shade -
which is exceptional in AAA ‘Gros Michel‘). Therefor, the planning of a root trial
should not calculate with the effort to proceed individual samples (Chapter 5.1:
large vs. small samples), but to proceed the total sample number required for each
soil coring method. 26
74
26 The development of %SE/M over sample amounts was calculated for the remaining Musa cultivars AAA ʻRedʻ, ABB ʻPelipitaʻ and AAB ʻCurraréʻ in the same way, though only for monolith method, in which they were sampled. The plantain ʻCurraréʻ and banana ʻRedʻ have slightly higher %SE/M than the other two. 75% natural shade has mostly higher %SE/M, stronger than shown for ʻGros Michelʻ in the Chapter 5.2.2. Minimal shade is sometimes similar, as shown above; and minimal natural shade shows highest variation amongst the cultivars, like high %SE/M (ʻGros Michelʻ), low %SE/M (ʻCurraré) and increasing instead of decreasing development (ʻRedʻ). The all-shade-level curves are very uniform. Separate shade levels have less divergences amongst them for max. sample amounts, like above, than for basic sub-groups. Invalid samples are max. 6 out of 48 (ʻRedʻ), thus must be considered.The root variable dry biomass per unit of soil (DBU) was analysed in the same way like RLD. The development of %SE/M over sample amounts react similarly than for RLD; although the %SE/M are constantly higher for DBU than for RLD.
5.3 Conclusion
The studying of very specific (root) traits in a very heterogeneous agroecosystem
is a challenge. A good knowledge of possible soil coring methods is necessary, to
choose an appropriate method. In our study, we are able to confirm, that the
number of samples is the most powerful aspect of coring methods, suggested by
Draye et al. (2005). Smaller samples inevitably have higher variability, i.e.
standard errors. And the closeness to the plant may counteract, as samples taken
at the area of highest root density (RLD), may be of the smallest size (Araya,
2005); otherwise, the soil volume tested must be remarkably large (Draye et al.,
2005). That is the more important, the higher the spatial variability of roots
becomes; commonly, that is higher, if the site heterogeneity is high (Lecompte et
al., 2005); which is most likely given in stressful conditions (Carr, 2009). We
observed, that the variability in our 75% plot was amongst the highest. However,
the tolerance to increase both efficiency and effectivity of coring is limited. To
remain in realistic sampling efforts, only low qualitative improvement may be
made. On the contrary, efficiency improvements directly impact the quality, which
is far too fast a negative impact. Next to the sampling pattern, a ‘synthesised‘
middle-sized and in its proportions changed core would gather even better fitted
results. Finally, the total roots (RLD) of all species (around AAA ‘Gros Michel‘)
plants are low, with <0,1 cm cm-3 (monoliths) and < 0,3 (auger samples).
In terms of Hypothesis 4, the divergences of %SE/M were complex for different
root variables or natural shade levels. Yet large samples (monoliths) were
advantageous in low %SE/M, though variation amongst shade levels or root
variables seems higher. The two methods draw near each other for high sample
amounts (230 auger samples, 46 monoliths) with <10 %SE/M. Intermediary
sampling intensities, slightly raised to 80-100 auger samples per-shade-level, and
16-20 monoliths, could be sufficient. Small samples are advantageous to be suited
into a densely grown system (positioning). Large and square, instead of circular,
samples seem to compensate the specialities of Musa root systems better, and the
tools for taking large samples are advantageous in customisation.
75
6. Root formation
Banana roots are rather sensitive to their immediate environment (Turner et al.,
2007), and as they prefer warmer temperatures, sun light and water (Draye, 2002),
a response to a deficiency of radiation under natural shading is assumed. Plants
maintain a ‘functional equilibrium‘ between their shoot and root biomass
(Swennen, 1984; Noordwijk et al., 2004). A deficiency in above-ground growth
resources, i.e. radiation, may lead to a preferred build-up of shoot biomass to
maintain photosynthetic carbon dioxide assimilation (Rao et al., 2004; Schroth,
1999). Also root build-up costs photosynthates (Turner et al., 2007), which may be
otherwise invested, and a humid tropical agroecosystem may be well supplied with
below-ground growth resources, i.e. water and nutrients (Draye, 2002). Yet high
natural shading is accompanied by densely occupied soil space by shade trees,
coffee and Musa; below-ground competition may influence the phenotypic root
development as well as shading. Turner et al. (2007) sees the shallow proliferation
of banana roots as a consequence of edaphic conditions, rather than genetic
determination.
According to Hypothesis 1, the banana and plantain have less root biomass in
high levels of natural shading (Chapter 6.1.1). According to Hypothesis 2, the
density and amount of Musa roots decreases in horizontal and vertical directions
from the rhizome (Chapter 6.1.2). In high natural shading, the root system is
shortened more, whilst the amount and density of roots of adjacent plants
increases (Chapter 6.2); and correspondingly, according to Hypothesis 3, banana
roots are strongly negatively correlated to tree and coffee roots. Genotypic
divergences are assumed to cause varying phenotypic responses.
In the course of the study, a method to estimate the whole banana root mat out of
soil cores shall be suggested (Chapter 6.3).
76
6.1 Musa root biomass
The density and amount of Musa roots will be studied for large samples
(monoliths) in response to natural shading (Chapter 6.1.1), and the distribution of
banana roots is analysed by small samples (auger; Chapter 6.1.2).
6.1.1 Allocation
A General Linear Model (GLM) was performed as a MANOVA to release
information about significant variation in Musa root formation. The monoliths of
AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘ and ABB ‘Pelipita‘ were
subject to the analysis. Thus, N = 46; N = 42; N = 46; N = 4627 respectively; the
monoliths taken include three Musa plant replications per level of natural shading,
and N = 4 monoliths per plant (occasionally invalid samples). The root variables
dry weight, length, volume (VOL), root length density (RLD), specific root length
(SRL) and dry biomass per unit of soil (DBU) were used.
Common for all MANOVA‘s conducted in the present study, they were done by
SPSS by IBM, and by original programme settings, such as Pillai-Trace, Wilks-
Lambda, Hotelling-Trace and Roy method to calculate the multivariate analysis.
The level of significance is < 0,05. The root variables used differ in the individual
cases, thus see each Chapter. Post-Hoc tests for significant factors were done as
Tukey and Duncan tests. The inter-subject effects (i.e. singular ANOVA‘s) had to
be considered as well, as they may differ from the multivariate analysis result. All
possible interactions were tested.
Results
Cultivar and natural shade levels both are significant. The interaction cultivar x
shade is harshly significant in MANOVA, though the inter-subject effects have no
significance for any root variable. Plant and replication number are significant as
77
27 Occasionally, ʻscannedʻ and ʻweighedʻ variables were not both missing, if sample lost in lab.
well, but the ‘direction‘, the sample was taken in, not. SRL in inter-subject effects is
contrary in (in-)significances to the other five root variables. Significant interactions
include mostly the factors plant, replication or direction, or are accompanied by
shade and cultivar.
Duncan tests form similar results as Tukey-HSD does for DBU and RLD (Annex
D). The Tukey test gives average means of sub-groups. In natural shade levels,
75% has no conformity to other levels, whereas the sequence of the others is
unexpectedly 50% < Min. < 25% (DBU). In RLD, the sub-groups are different, as
25% < Min (see also Fig. 15). VOL-variable develops similarly (no Post-Hoc
shown; Tab. 13). In the cultivar-Post-hoc tests (Annex D), the two dessert bananas
form one sub-group, the plantain and the cooking banana another. ‘Gros Michel‘
has lowest, ‘Curraré‘ highest root contents in samples (see also Fig. 15), thus
have no conformity. The root variable SRL develops mirror-inverted (Tab. 13).
VOL develops like DBU (Tab. 13). The plant-Post-hoc tests identify Musa plant 21
(‘Curraré‘) to have exceptional high root contents; and identify the plants 4 and 8
(‘Gros Michel‘), 28 (‘Curraré‘) and 48 (‘Pelipita‘) to have very low root contents,
together with several other ‘Gros Michel‘ and ‘Morado‘ plants (RLD). In DBU, the
plants 1 (‘Gros Michel‘) and 37 (‘Morado‘) additionally have high root contents in
monoliths. Replications are not a ‘functional‘ unit, but merely a ‘process-defined‘
Tab. 13 Musa root contents in monoliths for four natural shade levels and four cultivars AAA ‘Gros Michel‘,
AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘ and ABB ‘Pelipita‘. The root variables VOL and SRL were chosen, and
average mean ± standard error are given.
Root variable Shade Gros Michel Morado Curraré Pelipita
VOL [cm3] Minimal
25 %
50 %
75 %
SRL [cm g-1] Minimal
25 %
50 %
75 %
16,7 ± 2,96 48,8 ± 14,39 51,9 ± 8,13 35,5 ± 5,89
14,3 ± 2,29 47,4 ± 8,63 56,9 ± 9,78 45,7 ± 5,93
21,5 ± 4,72 29,5 ± 5,37 36,6 ± 10,10 28,1 ± 4,28
9,4 ± 1,94 15,3 ± 4,45 19,6 ± 7,08 15,6 ± 2,13
408,0 ± 34,32 275,9 ± 34,39 274,6 ± 19,90 247,4 ± 21,96
499,3 ± 42,52 268,5 ± 33,66 260,6 ± 55,60 214,8 ± 22,70
471,6 ± 79,44 2,8 * 104 ± 2,8 * 104 317,1 ± 17,97 242,3 ± 20,31
446,4 ± 62,75 466,0 ± 46,90 3.192,7 ± 2,64 405,9 ± 43,22
78
sub-group, thus were not considered. Analysed by box plots (not shown), ‘Curraré‘
seems to have the highest spread of values (upper and lower quartiles).
The ‘directions‘ from the experimental Musa plant, in which the monoliths were
taken, were not significant (thus not shown). The root contents appear like a
general ‘disorder‘. No singular peculiarity of inter-row (‘IR‘) or coffee-row (‘CR‘)
Fig. 15 Root content of Musa under four natural shading level and four cultivars, AAA ‘Gros Michel‘, AAA
‘Red‘ (‘Morado‘), AAB ‘Curraré‘ and ABB ‘Pelipita‘, in monoliths. For two root variables, DBU and RLD to
compare length and dry biomass trait of roots.
79
B.
A.
locations may be observed, in terms of higher or lower root contents (RLD, DBU);
or ‘adapted‘ roots by a VOL or SRL change. Analysed by box plots (not shown),
the spread of values of that ‘directions‘-sub-groups are much higher and more
variable than ‘normal‘ sub-groups (upper and lower quartile); particularly in
‘Curraré‘ and 25% shade, or the dessert bananas in minimal natural shade.
Discussion
The Musa root content gathered by the monoliths is significantly influenced by the
natural shade level, under which the banana plants are grown. In minimal and
moderate shading, the analyses are inconclusive, in terms to reveal the shade
management most beneficial to a strong root formation (Fig. 15, Annex D). For
‘Pelipita‘, RLD and DBU are always higher in 25%, and in ‘Gros Michel‘ both root
variables are always higher in minimal shading. At any rate, then a decline of root
contents takes place; a smooth reduction in 50% shade and a strong, uniform
reduction in 75% shade. We conclude, that excessive shading negatively impact
banana and plantain roots. On-farm shading may be less uniform and even more
deep than 75% shade; thus, to allow a solid banana root exploitation, such deep
shading should be avoided. Alongside that root content decline, the Musa shoot is
reduced strongly in size and biomass under high shading (Annex F; Chapter 3.2),
but more to this ‘plant equilibrium‘ in Chapter 7. AAA ‘Gros Michel‘ has lower root
contents than the other three Musa cultivars, especially its AAB ‘Curraré‘ pendant.
Thus, with lower Musa RLD, ‘Gros Michel‘ has apparently less nutrient and water
uptake-capable root interface. The studies findings are always confined to the root
content in samples, as the total root exploitation in its full extent was not studied.
These results now may raise the question, how strong the Musa root contents in
monoliths are reduced? The decline of RLD contents from minimal to 75% natural
shading is given in [%], accompanied by the RLD values (average means) shown
in Fig. 15 A., for each of the four cultivars. ‘Gros Michel‘ (RLD means in Chapter
5.1.2, Tab. 11) reduced by 52,2%; ‘Curraré‘ (0,041 to 0,020 cm cm-3) reduced by
51,2%; ‘Morado‘ (0,027 - 0,018 cm cm-3) reduced by 33,3%; and ‘Pelipita‘ (0,030 -
0,020 cm cm-3) reduced by 33,3%. Banana ‘Morado‘ and cooking banana ‘Pelipita‘
80
have higher RLD values in 25% than minimal shade (Fig. 15 A.); the decline of
that shade to 75% is 41,9% (‘Morado‘), and 41,2% (‘Pelipita‘). Thus, measured by
a root variable depending upon length, ‘Gros Michel‘ and ‘Curraré‘ have, though
the former has far less Musa root contents than the latter, similar reduction rates;
and ‘Morado‘ and ‘Pelipita‘ are alike each other. The decline of DBU contents is
given correspondingly: ‘Gros Michel‘ (0,09 to 0,03 g dm-3) reduced by 66,7%;
‘Curraré‘ (0,16 - 0,06 g dm-3) 62,5%; ‘Morado‘ (0,14 - 0,04 g dm-3) reduced by
71,4%; and ‘Pelipita‘ (0,12 - 0,05 g dm-3) 58,3%. The DBU values in 25% instead
of minimal shade are higher for plantain ‘Curraré‘ and cooking banana
‘Pelipita‘ (Fig. 15 B.); the decline of that shade to 75% is 71,4% (‘Curraré‘), and
72,2% (‘Pelipita‘). Given that, compared for their root biomasses, the dessert
bananas have a very alike and strong reduction in shade, and the cultivars with a
‘B genome‘ are similarly alike each other. The Musa DBU decline is up to three
quarter of the original values, and the Musa RLD declines only up to half of the
original values.
The first Discussion-paragraph describes the general development of Musa root
contents for either the factor shade, or the factor cultivars. The interaction of both
tested says, that the four cultivars have significantly diverse root contents due to
the shade levels tested. As named above, the interaction (shade x cultivar) is still
significant in MANOVA to 0,05 (level of significance), whereas the inter-subject
effects are not significant. If we assume the multivariate test to be more
‘authoritative‘, the cultivars react differently to natural shade: the strongest
divergences are to be seen in moderate shade (DBU), or up to 50% shade (RLD;
Fig. 15). Draye (2002) notes that such ‘synergetic architectural root variables‘ like
dry biomass (DB) or DBU are restrained in their conclusion to compare the root
proliferation of certain genotypes; as roots may change morphologically.
Belalcázar et al. (2005) reports Musa roots to become more voluminous, by
increased diameters, when mechanical impedances slows down their growth.
Lecompte et al. (2005) found Musa root diameters in root axes as well as in
laterals to be reduced under low light availability.
81
In this study, it was not possible for us to separate the root orders (axes, laterals of
1st, 2nd order etc.) to conclude their diameter changes; only an average diameter
development per sample would have been possible. We solved the situation in the
following way: the Musa VOL in monoliths primarily decreases under high natural
shading (Tab. 13), and develops like DBU (Fig. 15 B.). But this does not give
evidence to us, whether just less roots are to be found within the sample; or if the
individual roots are indeed thinner. The calculated root variable SRL assesses the
change in proportions of root biomass and corresponding length28: it increases
quite uniformly for 75% natural shade (Tab. 13). This development indicates, that
the Musa roots shift towards less biomass, compared to more length under high
natural shading. The following conclusions are possible: A. the Musa roots that
developed under low light availability are indeed thinner, which would imply that
less carbon is invested per root cm formed; or B. the root system in the whole is
smaller and exploits only less soil volume, so that more fine roots and high-order-
laterals are gathered in the samples; which are naturally thinner, have less
biomass and form more root length. In ‘Gros Michel‘ only, the SRL-development is
diverse (Tab. 13). Apparently, this cultivar has an unusual high length proportion in
general, compared to the others; and in 25% shade particularly. Two SRL-values
are exceptional high: ‘Morado‘ in 50% shade, and ‘Curraré‘ in 75% shade. In both
groups, one monolith each has very low DB contents, plant 35 (‘Morado‘) with DB
= 0,0006 g; and plant 24 with DB = 0,0013 g. Those excluded, SRL would be
246,0 and 558,029, respectively; which is very conform to the rest. The monoliths‘
impact upon ‘normal‘ root variables (VOL) is marginal, but in the ‘specific‘
calculated ones it becomes exceptional. Possibly stones or similar inhibitions in
the field caused those Musa root contents.
The insignificance of the factor ‘directions‘ was not very conclusive to give
information about the influence of the coffee row. No higher Musa DBU or RLD
were distinguished for inter-row (in line Musa - next Musa) than for coffee-row (in
line Musa - next coffee). We have to conclude, that at least in the topmost 20cm at
82
28 Chapter 1.3
29 In ʻCurraréʻ, a monolith of plant 28 has DB = 0,0286 g and thus is conspicuously low, and SRL without it would be 483,09 in 75%. The three monoliths named are often to be seen (Chapter 7).
a distance of 40-80 cm from the experimental Musa plant, the banana roots were
not particularly diverted or reduced by the coffee shrub roots. Possibly the coffee
roots are even more confined to the soil directly below the rows (compare Schaller
et al., 2003a); or the coffee roots are deeper rooting and possibly even displaced
there by the strong Musa roots in those particular soil areas. On the contrary,
shade trees are present even - though in low numbers - in minimal shading, so
their roots may have ‘overlaid‘ the spatial effect of the coffee shrub roots. As we
found the heterogeneity in edaphic components to influence our samples (Chapter
5.2), possibly that heterogeneity ‘overlays‘ an otherwise very small spatial effect of
coffee shrub roots. And as we found several significant interactions with the factor
‘direction‘ (e.g. x cultivar, x shade), one of those impacts may as well ‘tarnish‘ the
effect, as it simply may not be present. That is unexpected, but possible.
Last, analysed by box plots (not shown), the values were stronger spread for the
moderate natural shade levels, than for the 75% shade (upper and lower
quartiles). The ‘box‘ stretched about 0,2 g dm-3 DBU (‘Curraré‘ in minimal or 25%
shade), or 0,04 cm cm-3 RLD. Unexpectedly the values are less diverse in the 75%
plot, which we found to be apparently heterogeneous - measured by SE - in
Chapter 5.2. Thus we have to be careful, how we define heterogeneity.
6.1.2 Spatial distribution
A General Linear Model (GLM) was performed as a MANOVA to release
information about significant variation in Musa root distribution. The auger samples
of AAA ‘Gros Michel‘ were subject to the analysis. Thus, N = 58, N = 60; N = 57
and N = 55 for Minimal, 25%, 50% and 75% shade, respectively. Three Musa plant
replications per level of natural shading were taken, and N = 20 auger samples per
plant, in five repeated sampling positions. The root variables dry weight (DB),
length (LEN), volume (VOL), root length density (RLD), specific root length (SRL)
and dry biomass per unit of soil (DBU) were used. The level of significance is <
0,05; further information on GLM in Chapter 6.1.1.
83
Results
The depth (vertical distribution) is significant, whereas the distance (horizontal
distribution) is not significant. The interaction depth x distance is significant. The
factor ‘direction‘ from the Musa plant is insignificant. Shade is insignificant, but the
inter-subject effects would be significant to a raised level of significance, <0,1.
Plant and replication number are significant as well. The singular root variables in
this GLM become less uniform than in Chapter 6.1.1. SRL in inter-subject effects is
in major parts contrary in (in-)significances to the MANOVA; the further length-
depending variables (RLD, LEN) are e.g. insignificant for the factors plant and
replication. Significant interactions mostly involve the factors plant, replication or
depth. The interactions depth x shade is significant, whereas direction x shade,
distance x shade and particularly direction x distance are not significant.
The factor ‘depth‘ consists of only two groups, and a Post-Hoc tests had not to be
applied. The root content of AAA ‘Gros Michel‘ declines with both distance
(horizontal) and depth (vertical) from the plant (Fig. 16), only 50% shade is
exceptional in this respect (0-10cm depth; and the 80 and 120 cm positions). VOL
and DBU develop exactly like RLD, except minor divergences (in DBU and VOL,
the 120 cm in 50% shade is of highest value at all; in RLD (Fig. 16), this is the 80
cm position; in DBU, the 40/ 10 cm position has higher root contents than minimal
shading at the same position; in RLD and VOL, this is not the case (Fig. 16). SRL
develops mirror-inverted (Tab. 14). VOL average means are (given ± standard
error) of course less than in monoliths, as they are not standardised per unit soil:
40/ 10cm are 1,44 ± 0,45 cm3 in minimal (1,28 ± 0,47 in 75% shade); 40/ 20cm are
0,91 ± 0,35 cm3 (0,26 ± 0,11); 80/ 10cm are 0,93 ± 0,43 cm3 (0,79 ± 0,20); 80/
20cm are 0,35 ± 0,14 cm3 (0,12 ± 0,06); and 120/ 10cm are 0,88 ± 0,33 cm3 (0,14
± 0,05). The factor plant does not show sub-groups for length-depending
variables, but in VOL and DBU, the AAA ‘Gros Michel‘ plants 6, 9 and 11 have very
high root contents in augers, and 1; 4; 12 have very low root contents 30 , thus a
slightly diverse picture for shade levels is found. Replications are not a ‘functional‘
unit, but merely a ‘process-defined‘ sub-group, thus were not considered.
84
30 Tukey-HSD and Duncan tests are diverse in that GLM, and Tukey having less sub-groups than Duncan (e.g. DB, DBU).
Fig. 16 Root content in auger samples of AAA ‘Gros Michel‘ under four natural shade levels. For RLD, in
categories: distance (horizontal) from experimental Musa in [cm] (position of sample); and: depth (vertical) of
sample in [cm] from ground surface.
The ‘directions‘ from the experimental banana plants, in which the auger samples
were taken, are not significant (thus not shown).The root contents appear like a
general ‘disorder‘. No singular peculiarity in inter-row or coffee-row locations may
be observed, in terms of higher or lower DBU and RLD root contents. Analysed by
box plots (not shown), the spread of values is higher and more variable, if the
samples are sorted by ‘directions‘ (upper and lower quartiles). The ‘box‘ stretched
about maximal ~0,15 cm cm-3 (‘directions‘) or ~0,10 cm cm-3 (‘normal‘ sub-groups)
in RLD.
85
Tab. 14 Root contents of AAA ‘Gros Michel‘ in auger samples for four natural shade levels. The root variable
SRL was chosen, and average mean ± standard error are given.
Root variable
Shade 40 -- 10 cm 40 -- 20 cm 80 -- 10 cm 80 -- 20 cm 120 -- 10 cm
SRL Minimal
[cm g-1] 25 %
50 %
75 %
841,1 ± 145,4 908,2 ± 188,0 870,1 ± 182,0 461,4 ± 164,9 827,7 ± 207,8
604,3 ± 94,5 742,0 ± 63,8 682,1 ± 115,6 1.032,0 ± 179,1 841,3 ± 161,8
644,9 ± 87,0 1.127,5 ± 107,6 700,8 ± 101,3 912,1 ± 192,4 726,7 ± 165,8
840,8 ± 197,9 1.091,0 ± 400,5 1.130,0 ± 536,4 1.070,3 ± 256, 4 900,8 ± 255,9
Discussion
The AAA ‘Gros Michel‘ root contents within the auger samples are significantly
different due to their soil depth (vertical distribution), with the topmost 0-10 cm soil
layer having the higher root contents (RLD, DBU; Fig. 16). Therefor, our bananas‘
root mats appear to be very superficial, when we assume the root density to
decline accordingly in further depths. This impression is supported by the
insignificant divergences of banana root contents due to the distance from the
experimental plants (horizontal distribution). Conform to Araya (2005), thus, there
is the natural decline of Musa roots with increasing distance and depth from the
rhizome visible, as the insignificant decline (in horizontal distribution) is present
(Fig. 16), except in the unusual 50% shade. The pronounced horizontal root
proliferation is the one remarkable characteristic under moderate shade levels,
which is then only stronger reduced in excessive shading (Fig. 16). Apparently, the
root system of our bananas are relatively superficial, compared to other studied
distributions, like “40cm ‘effective rooting depth‘“ (Carr, 2009), or 70cm total
rooting depth (Blomme, 2000a). We may only refer to the samples, as we did not
involved the total root extent, but our results suggest, that only individual roots
may proliferate in depths of ~70cm. Draye et al. (2005) found horizontal root axes
to ‘go down‘ with age; possibly, our plants are too young for such rooting depths.
As Turner et al. (2007) found the shallowness in Musa to be rather an edaphic
determined, than plant inherent quality; thus, what conditions could cause the
shallowness in our case? On the one hand, the Musa roots could be directed
towards the mulch and litter layer upon the soil ground, which is fertile in nutrients
86
and organic matter (Swennen, 1984; Araya, 2005; Belalcázar et al., 2005); on the
other hand, the possibly deeper rooting coffee shrubs and shade trees could
confine the banana roots to the topsoil; that is to be analysed in Chapter 6.2. The
density of banana roots is highest in the ultimate proximity of the experimental
plant, which is confirmed by the significant interaction of depth and distance. Thus,
observations of Blomme et al. (2000b), who found most roots closer than 60cm to
the corm, or Araya (2005) may be confirmed.
The natural shade level, under which the bananas are grown, has no significant
influence upon the AAA ‘Gros Michel‘ root contents in the auger samples. That is
quite unexpected; the significance would only be given for a raised <0,1 level of
significance in the singular root variables‘ ANOVAs. This analysis describes the
general development for the factor shade, but the root contents in the five auger
locations is, naturally, very converse. Therefor the interactions should be troubled
to reveal the impact of natural shading upon the proportions within the banana root
system. Shade significantly interacts with depth. Apparently, the divergence in root
contents between topmost and lower layer underlies changes explainable by
shade levels. E.g. in 25% shade, root contents exceed those of minimal shade in
the 0-10cm depth, but are lower in 10-20cm depth (DBU, RLD; Fig. 16). Despite
that, shade does neither interact significantly with distance, nor with the direction,
the Musa samples are taken in. It seems as if the root density, which declines with
increasing distance from the plant, is not impacted in this decline by the level of
shade, the plants are grown under. But: is that so?
The proportions within the banana root systems do not seem to change in their
order, under deeper natural shade levels. Only the magnitude of the decline in
depth and distance changes. The decline is given in [%], together with the average
means of DBU (not shown otherwise) for minimal and 75% shade: 40/ 10cm are
(0,115 to 0,123 g dm-3) increased by 7%; 40/ 20cm are (0,080 - 0,020 g dm-3)
reduced by 75%, 80/ 10cm are (0,081 - 0,054 g dm-3) reduced by 33,3%; 80/ 20cm
(0,033 - 0,011 g dm-3) reduced by 66,6%; and 120/ 10cm (0,067 to 0,017 g dm-3)
reduced by 74,6%. Given that, in the closest position to the experimental Musa no
decline can be observed. The root system seems to be less exploited in soil
87
volume under high natural shade, as the deeper soil layers and the most distant
locations are most declined. We quantified also the ‘normal‘ decline, which may be
found in every level of shade. A. from the closest (40/ 10cm) to the most distant
position (120/ 10cm), the root contents in auger samples are in minimal shade
reduced by 42%; in 25% shade reduced by 56%; in 50% shade increased by 64%;
and in 75% shade decreases by 86%. B. the closest position (40cm) experiences
a decline from the topmost (0-10cm) to the lower (10-20cm) soil layer: in minimal
shading reduced by ~30%; in 25% by ~75%; in 50% by ~72%; and in 75% by
~84%. Therefor, the Musa root system is stronger confined around the
experimental plant under high shading (A.); and the vertical decline appears to be
as strong as the horizontal decline. In RLD, the corresponding declines in banana
root contents (given in Fig. 16) are in 40/ 10cm (0,064 to 0,061 cm cm-3) reduced
by 4,7%; 40/ 20cm are (0,038 - 0,021 cm cm-3) reduced by 44,7%; 80/ 10cm are
(0,063 - 0,036 cm cm-3) reduced by 42,9%; and 80/ 20cm are (0,022 - 0,012 cm
cm-3) reduced by 45,4%; and 120/ 10cm are (0,054 - 0,013 cm cm-3) reduced by
75,9%. Thus, in RLD, a weaker decline in depth is present than in DBU, but a
similarly strong decline in the most distant sampling location. The quantification
within the root system proportion finds A. closest (40/ 10cm) to most distant (120/
10cm) in minimal shade reduced by ~16%; in 25% shade decreased by ~35%; in
50% shade increased by ~50%; and in 75% shade reduced by ~79%. B. at the
closest position, 0-10cm compared to 10-20cm: in minimal shade reduced by
~41%; in 25% shade reduced by ~71%; in 50% shade reduced by ~33%; and in
75% shade reduced by ~66%. Given that, the LD is in general less reduced than
DBU, and otherwise the development is very uniform. The very closest auger
sampling locations undergoes almost no decline in root density or biomass, when
the plants are grown under high shading; whereas the most distant position is
reduced by three quarter compared to the original root content.
The response of banana roots may be expressed in a change of their length- and
biomass-proportions (compare Chapter 6.1.1), which we assess by the calculated
SRL root variable. The SRL average values are much higher (500 - >1000 cm g-1;
Tab. 14) obtained in auger samples, than in monoliths (Chapter 6.1.1, Tab. 13;
<500 cm g-1). Possibly, less structural roots (axes) were gathered by the auger,
88
compared to monoliths, by the inherent limitation of the tool size (Chapter 5.1.2).
As reference values, Blomme (2000a) named 4 to 1500 cm g-1; which is very
much like our results. The coring locations at the lower soil depth and particularly
the samples gathered under high shading, show strongly increased SRL. Possibly
more fine roots are to be found in those locations, whether normally or due to
smaller root systems in high shade, which are thinner and have less biomass per
root cm. Or, the change under high natural shade, may be caused by less carbon
being invested per root cm, the roots are thinned. Lecompte et al. (2005) found the
diameter reduction caused by low light availability to be more severe in the
periphery of the root system, as the closer parts seem to be best served; probably
this effect may be involved here. At any rate, AAA ‘Gros Michel‘ roots seem to be
‘regularly‘ thinner than those of other cultivars (compare ‘Morado‘; Chapter 6.1.1).
The factor ‘direction‘ was as insignificant here, as in the GLM before, and it is not
less unexpected. Even the interaction direction x distance was insignificant. On the
contrary to the monolith method, the auger positions in the ‘coffee-row‘ directions
(in line Musa - next coffee) were far closer to the coffee row. In fact, the 80cm
distant position was often ~10cm to the coffees‘ stems, and consequentially, the
120cm position was behind the coffee row. The strong decline in banana root
contents in those positions is only found in 75%; whether that is caused by coffee
row roots, has to be analysed in Chapter 6.2. The causalities may be similar to
Chapter 6.1.1. As there is no response to the spatial position of the coffee rows in
no shade level whatsoever, possibly the shade trees compensate this effect, or the
effect would only reveal itself in plots without any trees (0% shade). More likely,
the coffee shrubs do not displace the banana roots. Anyhow, nearby Musa plants
are unlikely to have manipulated the root content: A. they were even more distant
to the sample; B. the cultivars were planted randomly, and ‘Gros Michel‘ roots
(black and slender) are quite well to be separated from other cultivars.
The 50% level of natural shade produced highest root contents in several auger
samples, at this point visible by several analyses. As we observed no irregularities,
e.g. abnormal shoot growth or sample amounts in the lab, we only may conjecture
about the probable cause of strongly concentrated root growth at some place.
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6.2 Tree and coffee root biomass
Erythrina poeppigiana and Coffea arabica roots are analysed for their root content
within monoliths and auger samples (Chapter 6.2.1), and consequentially, whether
the banana roots and other roots are strongly correlated within the samples
(monolith and auger), will be inquired (Chapter 6.2.2).
6.2.1 Formation
A General Linear Model (GLM) was performed as a MANOVA two times, to give
information about the coffee and tree root abundance in monoliths (large) and
auger samples (small). Erythrina poeppigiana and Coffea arabica roots were not
separated. The monoliths in the vicinity of AAA ‘Gros Michel‘, AAA
‘Red‘ (‘Morado‘), AAB ‘Curraré‘ and ABB ‘Pelipita‘; and the auger samples close to
AAA ‘Gros Michel‘ were subject to the analysis. Thus, N = 46; N = 42; N = 47 and
N = 46, respectively; and N = 227 (auger)31. Three ‘Musa‘ replications per level of
natural shading and cultivar were taken, and N = 20 (auger samples) and N = 4
(monoliths) per plant (occasionally invalid samples). The root variables fresh
weight, volume (VOL), surface area (SA), root length density (RLD), specific root
length (SRL) and dry biomass per unit of soil (DBU) were used. The level of
significance is < 0,05; further information on GLM in Chapter 6.1.1.
Results
Monoliths32: the GLM is, like the next (auger samples) less uniform than those of
Chapter 6.1. Shade is significant in MANOVA, but the inter-subject effects are not
significant for any root variable (mainly length-depending). The Musa cultivar,
around which the monoliths were taken, is significant. Musa plant number is
significant, whereas replication and ‘direction‘ from the Musa plant is insignificant.
SRL is contrary to (in-)significances in major parts to other roots variables, and
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31 Occasionally, ʻscannedʻ and ʻweighedʻ variables were not both missing, if sample lost in lab.
32 Diverse root variables included in MANOVA. At least for monoliths, the in Chapter 6.1 used variables provide equal or similar results (shade, vicinity of cultivars).
DBU and RLD are occasionally different as well. The interactions shade x Musa
cultivar, and shade x direction are insignificant, whereas Musa plant x direction is
significant.
The results of the Duncan and Tukey-HSD Post-Hoc tests were equally diverse
(Annex E, A.). Natural shade only forms one sub-group in Tukey test, but for RLD,
a tendency towards highest ‘other‘ root content in minimal and 75% shade may be
observed (compare to Fig. 17 A.). In 25% and 50% shade, almost no difference
occurs. The Musa cultivars, around which the monoliths were taken, form two sub-
groups. Thus, a high ‘other‘ root content may be found around ‘Gros Michel‘ and
‘Curraré‘. Around ‘Gros Michel‘, the proportion of both root types within the
samples was mentioned in Chapter 5.1.2. The Musa plants 53, 43, 50 (and other
‘Morado‘ and ‘Pelipita‘) plants were surrounded by lower ‘other‘ root contents,
accordingly, whereas Musa plants 1, 21 and 29 (consequentially, ‘Gros Michel‘ and
‘Curraré‘) are surrounded by quite a lot ‘other‘ roots in auger samples (e.g. RLD).
The ‘directions‘ from the Musa plant were insignificant (thus not shown), and show
indeed some individual directions of raised ‘other‘ root contents. Nevertheless, no
specific peculiarities in inter-row or coffee-row directions may be distinguished, in
terms of lower or higher RLD, so that no regularity could be found. SRL develops
roughly mirror-inverted to the others, with average means <100 cm g-1 mostly, that
decrease down to 50 cm g-1 under high natural shade.
Auger: shade is significant in MANOVA, but not in the inter-subject effects. Depth
(vertical distribution) is significant. Distance (horizontal distribution), ‘direction‘ from
the Musa plant, in which the samples were taken, and Musa plant number are all
significant; though in inter-subject effects, the three factors are only significant to a
raised level of significance, <0,1. Musa replication number is not significant. SRL
in contrary to (in-)significances in major parts, and RLD and SA are occasionally
different as well. The interactions distance x depth, distance x direction, direction x
distance x depth are significant, as well as direction x shade.
The results of Duncan and Tukey-HSD Post-Hoc tests were equally diverse as
before (monoliths. Annex E., B.). Natural shade only forms one sub-group in Tukey
91
Fig. 17 Erythrina poeppigiana and Coffea arabica root content, for four shade levels and in the vicinity of four
Musa cultivars, in A. monoliths, and B. auger samples. The root variable RLD was chosen. In B., two natural
shade levels were chosen exemplary, minimal and 75% shade. For RLD, in categories: distance (horizontal)
from experimental Musa in [cm] (position of sample); and: depth (vertical) of sample in [cm] from ground
surface.
test, but for RLD, a tendency towards highest ‘other‘ root contents in 50% and
75% shade may be found (compare to Fig. 17 B.). Minimal shade apparently has,
due to this test, lowest ‘other‘ root contents. The depth only consists of two soil
layers, and much higher ‘other‘ root contents are to be found in the topmost
0-10cm (Fig. 17 B.). The proportions within the samples of both root types was
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B.
A.
named in Chapter 5.1.2. The Musa plants 5, 7 and 11 are surrounded by fewest
‘other‘ roots, whereas Musa plants 6 and 9 are surrounded by the most ‘other‘
roots (RLD, DBU). The distance from the Musa plant, in which the auger samples
were taken, produces diverse Tukey-tests (Annex E., B.); but the lowest ‘other‘
root contents are always to be found at 40cm from the banana. The ‘directions‘, in
which the samples were taken, show higher ‘other‘ root contents in the coffee-row
positions, and lower ‘other‘ root contents in both inter-row positions (Annex E., B.).
SRL develops unsteadier for ‘other‘ root contents in auger (not shown), and forms
100-600 cm g-1. Average means distinguished for ‘directions‘, show 166 and 249
cm g-1 (both coffee-row directions), and 250 and 306 cm g-1 (both inter-row
directions).
Discussion
The root content of Erythrina poeppigiana and Coffea arabica is rather diversely
distributed in both the auger samples and the monoliths. It makes predictability
very difficult as well as linking the ‘other‘ root to the Musa root content. The natural
shade level, under which Musa and coffee plants are grown, is significant in the
MANOVA, but the singular root variables are not. The sequence of the shade level
thereby is unexpected. In monoliths, the ‘other‘ roots seem to be most abundant in
minimal as well as 75% shade. The RLD (average means given; shown in Fig. 17
A.) are, for around which Musa cultivar collected, in minimal to 75% shade: ‘Gros
Michel‘ 0,072 to 0,038 cm cm-3; ‘Morado‘ 0,048 - 0,034 cm cm-3; ‘Curraré‘ 1,293 -
1,983 cm cm-3; ‘Pelipita‘ 0,028 to 0,037 cm cm-3. Thus, the ‘other‘ root presence
among both shade levels is very similar indeed. In DBU, accordingly, ‘Gros Michel‘
1,015 to 1,250 g dm-3; ‘Morado‘ 0,998 - 0,706 g dm-3; ‘Curraré‘ 1,293 - 1,983 g
dm-3; ‘Pelipita‘ 0,601 - 0,771 g dm-3. The standard errors (not shown) are higher for
DBU. Given that, the higher abundance of ‘other‘ roots in 75% shade is
predominantly visible for the biomass proportion. This suggests that the relative
competitiveness, which is given by the uptake capacity and related to the root
length, is less stronger in 75%, than the structural constituent. The stronger coarse
root part possibly implies deeper rooting, possibly accompanied by mechanical
impedance to banana roots; but these (Chapter 6.1) did show no such sign.
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So far, the Musa and ‘other‘ root contents do not seem to be clearly mirror-inverted
in the monoliths, except the slightly higher abundance of ‘other‘ roots in 75%
shade, compared to the Musa root shortage in Chapter 6.1.1 in 75% shade.
Possibly the trees root so deep, that we mainly gathered coffee roots throughout
the four shade levels in our samples. Or the coffee shrubs have less roots in 75%
shade also, and more tree roots then are measured. We hardly found Poró roots
with nodules within our samples. Except that we may only conjecture currently.
How is the complementarity of both root type constituents in auger samples? The
significance of the natural shade level, the plants are grown under, and the
apparently higher ‘other‘ root abundances in 75% suggest a stronger divergence
to minimal shade. The RLD (average means; shown in Fig. 17 B.) of minimal to
75% shade are, for each sample position: 40/ 10cm are 0,143 - 0,144 cm cm-3; 40/
20cm are 0,054 - 0,035 cm cm-3; 80/ 10cm are 0,259 - 0,166 cm cm-3; 80/ 20cm
are 0,077 - 0,034 cm cm-3; 120/ 10cm are 0,179 - 0,160 cm cm-3. As the Fig. 17 B.
already indicates, the 75% shade does by no means feature much higher ‘other‘
root abundances than minimal shade. Compared to 25% and 50% shade (not
shown), the picture is overall rather uniform. But the 10-20 cm depths contain
under high shade less ‘other‘ roots than in minimal shade, like in Musa observable;
thus A. the major soil layer for Erythrina poeppigiana and Coffea arabica root
distribution of the tested ones seems to be 0-10cm, like for Musa; and B. the
shade tree and coffee roots do not seem to ‘fill‘ the gaps aggressively, which
evolve of the drawing-back banana root system in 75% shade; not more than their
‘normal‘ share of the respective sample location. In DBU, accordingly, 40/ 10cm
are 3,48 to 2,07 g dm-3; 40/ 20cm are 0,33 - 0,28 g dm-3; 80/ 10cm are 2,34 - 3,14
g dm-3; 80/ 20cm are 1,46 - 0,58 g dm-3; 120/ 10cm are 2,63 - 2,38 g dm-3. Also in
a biomass-depending variable, the decline of ‘other‘ roots in minimal shade is non-
existent.
Most abundant coffee and tree roots were are found around ‘Curraré‘ and ‘Gros
Michel‘ in monoliths (data before, and Fig. 17 A.), throughout the natural shade
levels we studied (RLD, DBU). The plantain ‘Curraré‘ had itself highest root
contents in monoliths, whereas ‘Gros Michel‘ were lowest (Chapter 6.1.1).
94
Possibly, the ‘other‘ roots do not impact the Musa roots, as the stronger formation
of roots in the cooking banana and plantain are not covered in any diverse
magnitude of root formation. Measured by SRL, ‘Gros Michel‘ has particularly thin
roots (Chapter 6.1.1), and ‘Morado‘ roots are particularly thick; but that does not
explain the other two cultivar‘s root formation by ‘other‘ roots. ‘Gros Michel‘ and
‘Curraré‘ were conform in one aspect (Chapter 6.1.1): the quantified decline of
their root contents from minimal to 75% shade, by ~50% in RLD. Possibly, the high
‘other‘ roots surrounding supported that stronger decline.
There appears to be some kind of ‘conformity‘ in the proportions of both root types
in the auger samples (Fig. 17 B.; data above). Naturally, when the planting
positions of coffee shrubs and Musa plants are considered, the more distant
positions from the bananas have more ‘other‘ roots. We did indeed find such
raised root contents, in both soil layers tested. Nevertheless, a displacing root
content of ‘other‘ roots is unlikely.
The calculated SRL may turn out complex to be used as a descriptor for ‘other‘
roots. Erythrina poeppigiana and Coffea arabica may have a generally diverse
specific root length by their genotypic determination. However, the SRL seem very
uniform, and it is in both sampling methods far smaller than those of Musa
(Chapter 6.1), that we found. Thus, the roots are heavier and thicker. It is difficult
to find regularities in the formation of SRL. The biomass constituent seems rather
unequal; which in monoliths may be caused by the coarse ‘trunks‘, that were
included in the analyses. The reduced SRL in monoliths for high shade levels
induces a presence of more structural, instead finer roots there.
The SRL is though distinguishable for ‘directions‘, which were for the first time
significant; and this in auger samples. This indicates, A. there are finer ‘other‘ roots
to be found in the inter-rows, more structural in the coffee-rows; which seems
logical, if the high-order-laterals are most distant from the coffee plant. B. the
Musa plant does not seem changed by the ‘directions‘ as much, as the other
species are influenced by the Musa. That may show the present competitive
balance, or the ‘other‘ root content is not a useful indicator to describe Musa roots.
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6.2.2 Correlation to Musa roots
The correlation coefficients (CC) and linear regressions (LG; not shown) were
calculated between the Musa root content and the Erythrina poeppigiana and
Coffea arabica root abundance within monoliths (large) and auger (small)
samples. The monoliths of AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘
and ABB ‘Pelipita‘ were subdued to the analyses, thus N = 46; N = 46; N = 42; N =
4633; respectively, and the auger samples of AAA ‘Gros Michel‘ were studied, with
N = 229. Three Musa replications were chosen per natural shade level and
cultivar. Erythrina poeppigiana and Coffea arabica roots were not separated. The
five root variables fresh weight (FW), volume (VOL), root length density (RLD),
specific root length (SRL) and dry biomass per unit of soil (DBU) were decided for.
Correlation coefficients are -1 (strongly negative correlated) < 0 (uncorrelated) < 1
(strongly positively correlated); whereas coefficients of determination are r2 ≤ 0,3
(uncorrelated); ≤ 0,8 (weakly correlated) and ≤ 1(tightly correlated). Independent
variable was Musa roots.
Results
CC do not exceed -0,26 (‘Pelipita‘ and VOL, Tab. 15). In auger samples of ‘Gros
Michel‘, CC are positive, as they are for RLD in monoliths. LR, naturally develop
Tab. 15 Correlation coefficients (CC) for monolith and auger samples in four natural shade levels, between
Musa root content and Erythrina poeppigiana and Coffea arabica root content. The root variables FW, VOL,
SLR, RLD and DBU were chosen, and AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘, ABB ‘Pelipita‘
for monoliths, and AAA ‘Gros Michel‘ for auger samples.
Analysis Root variable
Gros Michel Gros Michel Curraré Morado PelipitaAnalysis Root variable
auger monolithsmonolithsmonolithsmonoliths
CC FW 0,121 -0,102 -0,144 -0,145 -0,257
VOL 0,089 -0,031 -0,140 -0,043 -0,256
RLD 0,196 0,150 0,079 -0,033 0,056
SRL 0,116 -0,148 -0,112 -0,089 -0,163
DBU 0,122 -0,194 -0,165 -0,074 -0,191
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33 Occasionally, ʻscannedʻ and ʻweighedʻ variables were not both missing, if sample lost in lab.
equally, and no r2 > 0,07 (‘Pelipita‘, VOL and FW; others not shown) are to be
found, but mostly 0,01 < r2 < 0,04. Auger samples are not of lower CC or r2 than
monoliths (only SRL, DBU, DB). ‘Curraré‘ is not of less CC or r2 than ‘Gros Michel‘;
though root variables are diverse in that aspect, with RLD, SRL and DBU higher
for ‘Gros Michel‘. Point clouds were rather unshaped (not shown).
Discussion
The relationships between Musa root contents and tree and coffee root
abundances within samples are for all studied groups uncorrelated, with no CC >
0,3. The R2 of LR does not explain more variation in root contents than 7%, which
is very low indeed. Thus, none of that relations confirms that the root density and
amount of adjacent plants, i.e. Erythrina poeppigiana and Coffea arabica, are in
this case related to the relative competitive circumstances; if we would assume
they do, at least the proportional change in the composition of a sample is not
consistent over four levels of natural shade. The correlations are at any rate
negatively, thus Musa root contents decline if other roots‘ contents increase; yet
RLD is always positively correlated. Maybe that indicates a divergence in the
development of root variables; but until now, no evidence was given to assume the
development of root amounts (DBU) differently from the density of their length
(RLD) in such a way.
‘Curraré‘ and ‘Gros Michel‘, which had so different own root contents (Chapter
6.1.1), and so equal additions of tree and coffee roots (Chapter 6.2.1), are not
obviously diversely correlated. Though for ‘Gros Michel‘, the relation is slightly
stronger negatively correlated for major root variables, like DBU; but the difference
is so small, that assuming it to account for low ‘Gros Michel‘ contents in Chapter
6.1.1 would seem very confident indeed. Auger samples, however, are positively
correlated in its Musa and other root content; thus when Musa root contents
increase, other root contents would increase as well. Possibly the second soil
depth, 10-20 cm, influenced the relation in that way, or the 120cm distant sampling
locations (compare Chapter 6.2.1).
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6.3 Estimation of total Musa root system
In the course of the study, we found it challenging to try, whether we could
estimate the whole root mat of our bananas by using just the soil cores taken. To
calculate shifts within the ‘functional equilibrium‘ of Musa plants, we would need an
‘absolute‘ amount of root system size, to complement the total dry shoot biomass
of bananas. To valuate the root mat competitiveness, root variables like length or
volume interested us as well, as dry biomass. (Total root system = TRS).
A geometrical form was developed around the Musa experimental plants, which is
congruent with a set of auger samples (N = 20), thus it was done for AAA ‘Gros
Michel‘. As the rooting depth of Musa plants may exceed 20 cm in depth, a ‘third-
depth-sample‘ was introduced. It is situated only at the 40 cm sample positions
and beneath the existent ones (Fig. 19); so that the whole figure reassembles a
pyramid. As the root content in both existent layers was significantly lower in the
10-20 cm than in 0-10 cm (Chapter 6.1.2), the root contents were decided to be
described by exponential functions (Fig. 18) of the type:
Fig. 18 The root content of two auger sampling positions per direction of Musa plant in 75% natural shade,
described by exponential functions. The root variable DBU was chosen to demonstrate the methodology. N =
3 for each sampling position. Sampling positions are 0-10 cm and 10-20 cm depth (vertical) at 40 cm distance
from the Musa (horizontal) plant. Type of functions: Y = b * ecx.
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with y = root content in auger sample, x = depth of sample
And by those, the root content of the ‘third-depth-sample‘ was computed, as if we
assumed it to be a normal sample, ‘virtually taken‘. The root variables fresh weight
(FW), dry biomass (DB), length (LEN) and volume (VOL) were chosen. Before
applying the exponential functions, they were standardised for a unit of soil (like
we usually did for DB, i.e. DBU; [dm-3]). Each ‘direction‘ of the Musa plants was
treated separately per level of natural shade, thus N = 3 (occasionally invalid
samples).
By that we increased per Musa plant of ‘Gros Michel‘ to N = 24. Every auger
sample was attributed to a volume of soil it represents, shaped as a quarter ring
around the Musa plant in the centre (Fig. 19). The auger sample root content was
multiplied with that soil volume [dm-3] and the whole soil volumes of the pyramid
then added - that is, their root content, actually. The separate ‘directions‘ from the
Musa per level of shade were brought together to one average TRS per level of
natural shade. The shape and size of the quarter rings may be seen in (Fig. 19);
Fig. 19 The ‘pyramid figure‘ is attributed to an enlarged set of auger sample positions (N = 20 + 4), and forms
the TRS. Blue = the ‘third-depth-sample‘. A ring is 10 cm deep; it is 40 cm in ‘radius‘, thus e.g. for the third
distant ring from 80 cm to 120 cm from the Musa plant. Left, top: the soil volume inherited by each quarter
ring. Left, bottom: the soil volume of all rings per distance, i.e. three rings at 40 cm sample positions.
99
each has an auger sample position in its centre; thus 40 cm in radius, 10 cm in
depth.
Then, consequentially, we now know the TRS of ‘Gros Michel‘ in four natural
shade levels each, and for the root variables FW (TRB-fresh), DB (TRB-dry), LEN
(TRL) and VOL (TRV). We calculated now the share of one monolith (average of N
= 12) of the TRS (%M/TRS); that is (exemplary) 0,847% in Min., 0,345% in 25%,
0,417% in 50% and 0,679% in 75% for DB (VOL, LEN, FW not shown). The %M/
TRS evolving we applied to the other three cultivars; the root content of their
monoliths was multiplied with that factor to get the TRS for each of the four root
variables. As the TRS is not longer standardised per unit of soil, the un-
standardised units (e.g. DB instead of DBU) were used for %M/TRS.
Additional, the % TRB-dry of TRB-fresh was calculated; initially for ‘Gros Michel‘;
which is 6,39% in Min., 6,50% in 25%, 6,13% in 50%, and 7,35% in 75%. We used
it to spare the whole calculation path of FW for the three other cultivars, but we
applied that factor to get the TRB-fresh easily. For ‘Gros Michel‘, as we did both,
we were able to re-check the accuracy of that short-cut estimation.
Tab. 16 Total root system (TRS) estimated by auger sample method for AAA ‘Gros Michel‘ and by those, the
%M/TRS, and then the TRS of AAB ‘Curraré‘, ABB ‘Pelipita‘, AAA ‘Red‘ (‘Morado‘). The root variables are LEN
(TRL) and FW (TRB-fresh).
Analysis Root variable Shade Gros Michel Curraré Morado Pelipita
Estimation TRL [m] Minimal 1.311,82 2.393,39 1.470,56 1.762,21
25 % 1.307,22 2.813,34 2.222,26 2.420,48
50 % 1.608,62 2.367,00 1.180,15 1.510,16
75 % 621,53 1.061,78 98,33 1.116,46
TRB-fresh [kg] Minimal 2,89 5,18 4,09 4,06
25 % 3,28 17,04 9,14 14,24
50 % 4,82 8,05 5,41 7,07
75 % 1,20 2,16 1,27 1,81
100
Results
The TRL and fresh-TRB are high (< 1000 m, except 75% shade; and > 3,2 kg,
correspondingly; Tab. 15)34. The TRV are maximal 16268 cm3 (‘Curraré‘), and
minimal 1811 (‘Gros Michel‘) to 3265 cm3 (‘Curraré‘) in 75% shade; and TRB-dry
are confined to 88 g (‘Gros Michel‘) to 159 g (‘Curraré‘) in 75% shade (Fig. 20).
The TRS decline for 75% natural shade in all four cultivars. ‘Gros Michel‘ has
Fig. 20 TRV (B.) and TRB-dry (A.), estimated for the cultivars AAA ‘Gros Michel‘ (auger); AAB ‘Curraré‘, ABB
‘Pelipita‘, AAA ‘Red‘ (‘Morado‘), made by (%M/TRS).
101
34 The singular monoliths so exceptional in Chapter 6.1.1 (ʻCurraré: Plant 24, 28 (75% shade); and ʻMoradoʻ: Plant 35 (50% shade)) were not excluded in TRS-calculations, as their influence is small.
A.
B.
lowest TRS for the four root variables chosen, whereas ‘Curraré‘ provides the
highest TRS values. The ‘third-depth-sample‘ in ‘Gros Michel‘ varied in 0,17 g DB
in one ‘direction‘ to 26,63 g in another (minimal shade; N = 3); although the
average root content was 12,53 g in minimal shade, compared to an average
TRB-dry of 184,44 g (also Fig. 18 A.). After calculating the root content in each
ring of the ‘pyramid‘, the 40-80 cm (middle) and 80-120 cm (outer) rings have
increased total root amounts, compared to the 0-40 cm (inner rings). But the root
density was assumed to be highest in the closest rings to the Musa plant. That is
of course misleading, because the soil volume, the root contents response to, are
far larger (Fig. 19; 1206,4 (middle) or 1005,2 (outer ring) [dm3]) is far larger for the
distant rings; but the relative root content is still smaller. Indeed, for ‘Gros Michel‘,
the root content of the auger samples basically used to calculate the ring root
content, declines as anticipated for minimal, 25% and 75% natural shading.
Exemplary in minimal shading, the root length density declines as 63,95 cm cm-3
(40 cm (horizontal) -- 10 cm (vertical) position) to 63,44 (80 -- 10 cm) to 54,44 cm
cm-3 (120 -- 10 cm); and 36,15 (40 -- 20 cm) to 21,78 cm cm-3 (80 -- 20 cm). Only
in 50% shade, 47,98 cm cm-3 (40 -- 10 cm) is indeed followed by 84,49 (80 -- 10
Fig. 21 TRS in DB of AAA ‘Gros Michel‘ for two of four natural shade levels: A. 25% and B. 75% shade. The
‘absolute‘ root content in 0-10 cm (black), 10-20 cm (medium grey) and 20-30 cm (light grey) depth. For inner
(0-40 cm), middle (40-80 cm) and outer (80-120 cm distant) rings.
102
B.A.
cm) and 71,98 cm cm-3 (120 -- 10 cm); but that is singular. The phenomena is
shown in (Fig. 21); additional, A. the minor root content of the ‘third-sample-depth‘
ring (bright grey); and B. the strong decline in 80-120 cm ring root content under
75% natural shading.
Discussion
The TRS we evolved should be compared to other scientists‘ observations, to
evaluate our estimation. Araya (2005) found in commercial Costa Rican banana
plantations the cvs. ‘Yangambi Km5‘ to have 3584 g and ‘Valery‘ 892 g (lowest of
cultivars studied; known to be small), root fresh weight per plant. ‘Gros Michel‘ had
approx. 2250 g root fresh weight as an average of 10 plants; which is very close to
our bananas in minimal shading (Tab. 16; age of Araya‘s plants unknown). The
25% shade level TRB-fresh appear rather peculiarly high. Serrano (2005)
measured in commercial plantations of Costa Rica the functional root fresh weight
content per plant, given in an average mean per region: 8-87 g in Sarapiquí,
43-102 g in Pococí, 36-81 g in Guácimo, 36-135 g in Siquirres, 35-143 g in Matina,
31-114 g in Talamanca. Presumed this involves mostly fine roots, the TRB-fresh of
our bananas could well be 1-4 kg higher (Tab. 16) or more, as structural roots form
the major biomass proportion. Blomme (2000a) found max. 0,5 kg root dry
biomass at flowering (bananas, plantain; including suckers) and Mukasa et al.
(2005) 0,39 - 0,97 kg root dry weight per plant, in 8 Musa genotypes beyond the
3rd ratoon cycle; both studies took place in Africa. Those TRB-dry are very similar
to our TRB-dry results (Fig. 20 A.). The total cord root length was studied by
Blomme (2000a) to be 10,2 m in ‘Mbi Egome‘ or 10,8 m in ‘Calcutta 4‘ (plant age
60 weeks); Mukasa et al. (2005) found 10,5 - 20,2 m in the before mentioned 8
Musa genotypes. Our TRL are comparatively peculiarly high, but included lateral
roots (to > 1 mm diameter) as well; and as fine roots make the major share in TRL,
that may result in generally higher TRL values; anyway, our length-dependent TRS
may be slightly over-estimated.
Naturally, we risked to over- or underestimate the ‘true‘ root amount of a whole
system as an inherent quality of any interpolation. Particularly by ‘transferring‘ the
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%M/TRS factor; and the %TRB-dry of TRB-fresh descriptor from ‘Gros Michel‘ to
the three other Musa cultivars. The TRB-dry (Fig. 20 A.) is in 50% shade higher
than in minimal shade for all four cultivars. Compared to the DBU-development in
Chapter 6.1.1, this particular sequence of our natural shade levels is only to be
found in AAA ‘Gros Michel‘. Apparently, the other cultivars ‘inherit‘ this peculiarity
during the estimation process; whereas the TRB-dry values in other shade levels
seem rather consent (25% shade, 75% shade). As we decided to use the auger
sampling as the basic method, there was not alternative option. We thought, what
may be justified by Chapter 6.1.2, that it better represents an internal distribution
of root densities and amounts, within the individual Musa plant root system. When
in any future study a possibility would be given, to prove the auger sample set on a
later excavated Musa root system, it would do a great deal to assess the
closeness between both methods.
The ‘third-depth-sample‘ ring offers a very low root content, compared to the
residual TRS (Fig. 21), and is also very variable in its calculated results of the
exponential functions. At least in those shallow banana mats it does not seem
entirely necessary. However, A. Blomme (2000a) stated shoot- and root- biomass
comparisons require ‘absolute‘ values, thus every step to more ‘realistic‘ values is
desirable; B. whenever the system may be of use, it may have to be applied to
deeper rooting Musa plants. Yet it requires some considerable effort to achieve the
results.
The share represented by an individual, averaged monolith of the TRS (%M/TRS)
is well <1% for all our studied groups (in DB; in LEN < 0,3%; in VOL < 0,6%). The
closest auger sample, 40 cm (horizontal) and 0-10 cm (vertical), has not more than
0,1% (FW; all not shown). In both methods, those close samples have more
content of the TRS in 75% shade, than it has in all other levels; that may support
the observation of Chapter 6.1.2 and the SRL-development of Chapter 6.1.1, that
the 75%-shade-Musa‘s exploit less soil volume and stay more concentrated
around the individual Musa plants. Blomme (2000a) found his 39263 cm3 large
cores up to ~ 1,4% root dry weight and up to ~ 2,7% cord root length; Mukasa et
al. (2005) in the same cores up to ~ 8,1% and up to ~ 7,1%, respectively; the
104
former in sandy Nigerian, the latter in compact loamy Ugandan soils. The Nigeria
%M/TRS, if broken down to smaller monoliths like ours, indeed describes <1% of
the TRS; thus, our estimation seems likely. Only that we expected our %M/TRS to
reach a level equal to that of the Uganda soil, as we anticipated a higher impact
upon root formation by the loamy, clayey texture of our soils. Mukasa et al. (2005)
interpreted the stronger concentration of roots within the monoliths to be such an
effect of an restrictive soil (Uganda).
The behaviour of TRL, TRV and TRB naturally is very much like the initial samples‘
root content, which was analysed in Chapter 6.1.1 and 6.1.2. ‘Gros Michel‘ TRS‘
values behave very accordingly to both previous Chapter; but as the basis of the
estimation, that is not surprising. Yet the root amount and density is ‘magnified‘, so
specifics are better visible. The sequence of root amounts in shade levels in the
cultivars ‘Morado‘, ‘Curraré‘ and ‘Pelipita‘ having higher 50% than minimal shade
root amounts was named before. Another may be, that AAA ‘Morado‘ apparently
has very voluminous roots (Fig. 20 B.). The TRV of this cultivars is almost as high
as that of AAB ‘Curraré‘ or ABB ‘Pelipita‘; but in the other root variables, e.g. the
TRB-dry (Fig. 20 A.), ‘Morado‘ seems much more alike ‘Gros Michel‘. At any rate,
we did observe during our work, that ‘Morado‘ had thicker roots, and ‘Gros Michel‘
rather thinner ones.
6.4 Conclusion
The competitive balance in a mixed-species system is impacted by many sources
and effects of interactions, of both environmental and plant components. It needed
a considerable number of diverse perspectives to find out, why exploit our Musa
plants less soil volume and have smaller root systems under high natural shade?
(Chapter 6.1). The distribution of roots, so Schroth (1999), is likewise cause and
effect of root competition. Are our bananas restricted by root competition, or do the
banana plants response to a reduced light availability? The pro‘s and contra‘s may
be weighed up against each other.
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The key to a successfully combined choice of species is the ‘complementarity‘,
due to which the species segment the available below-ground space and growth
resources (Schroth, 1999; Schaller et al., 2003a; Rao et al., 2004). In both soil
layers we tested, all both root types are found mainly in the upper one. In every
sample we took, both root types were found; occasionally, banana roots lacked
(Chapter 5.1.2). Thus the possibility for competition is given, and intermingling
instead of pure replacement likely (compare Schroth, 1999). The auger method
draws a picture, which three-dimensional represents the planting position of each
species. Musa roots are most concentrated around the rhizome, whereas the
share of ‘other‘ roots increases most distant to the Musa. The Musa roots are
equally spread in all ‘directions‘ of the plant, but the ‘other‘ roots share is higher
close to the coffee-row, than in inter-row positions. That implies, that Musa rather
would influence a coffee root displacement, than coffee shrubs could displace
Musa roots. Of no root types a displacement into depth could be found. In both
sampling methods, no ‘complementarity‘ in the sense of shade levels with highest
root abundances could be observed.
The highest natural shade level, which causes an apparent decline in banana
roots, does only have few apparently additional ‘other‘ roots. As Turner et al.
(2007) suggested in a shade extent of that kind light deficiency would be the
determining limiting factor to banana growth, it seems unlikely to attribute the
visible root decline to root competition. According to the authors (Turner et al.,
2007), in moderate shade other factors may become restricting. In minimal and
25% shade, both root types, Musa alike ‘other‘ roots, were hardly sortable to a
realistic pattern. Perhaps this diverse, heterogeneous growth is enabled by a close
‘complementarity‘ between the species. Therefor we ultimately correlated the root
type proportions in every sample, but in neither coring method was any correlation
detectable. Due to those facts, we are inclined to hold the plant response to a light
deficiency responsible for the smaller Musa root system under high natural shade
(75%); whereas the Musa root formation in moderate shading levels (minimal and
25%) may be influenced by many more factors. The only accordance seems to be,
that the magnitude of decline (minimal to 75% shade) in root contents is each
similar for cvs. AAB ‘Curraré‘ and AAA ‘Gros Michel‘, surrounded by many ‘other‘
106
roots (>50%), and AAA ‘Morado‘ and ABB ‘Pelipita‘, surrounded by fewer ‘other‘
roots (33%).
The relative morphological conditions of the Musa roots then gives evidence of the
competitive root balance in the mixed-species system. Mechanical impedance is
reflected by thickened banana roots, reported by Draye (2002) and Araya (2005).
No thickened roots in high natural shade or in the periphery of Musa root systems
could be found. The response of Musa to low light conditions may be reflected in
roots by thinned roots, so Lecompte et al. (2005). We found less biomass per cm
root in high natural shade. Therefor this seems consequent, except that we may
only have got more finer roots in the samples, as the root systems are smaller.
The laterals emerge in a central section of the root axes (...), thus this seems only
partially an explanation. The essential problem about this aspect is, that there is
an apparent flaw in understanding the mechanisms (Schroth, 1999), by which the
roots of alternate species are ‘repulsive‘ against those of other species. By which
means could Musa roots be possibly confined by other root systems, and what
kind of effects (root diameter, concentration of roots, ...) arouse?
In terms of Hypothesis 1, the banana and plantain root density and amount is
reduced in high natural shading (> 75%). The plantain and the cooking banana
have denser and more roots than the dessert bananas. In 25% and minimal
shading, highest root contents occur in auger samples and monoliths. In terms of
Hypothesis 2, the density and amount of banana roots decreases with depth
(vertical) significantly, and decreases non-significantly with increasing distance
(horizontal). In highest natural shading (> 75%), the root system is most shortened
in all sampled positions. The density and amount of adjacent plants‘ root increases
poorly in highest natural shade, but the highest root contents in monoliths occur
also in minimal shading. No stronger conformity is detectable. The highest ‘other‘
roots content is around a dessert banana and a plantain, which had significantly
the lowest (former) and highest (later) Musa root contents. In terms of Hypothesis
3, Musa roots and ‘other‘ roots are not (mainly negatively) correlated.
107
7. Below- and above-ground relations
Akinnifesi et al. (2004) and Blomme (2000a) mention that the shoot and the root
biomass of a plant may be reduced under certain unfavourable conditions. That
the root biomass within our samples was reduced under high natural shade, we
showed already (Chapter 6). We wanted to know, whether the shoot biomass is
reduced similarly or even less. Shoot-root ratios were used for agroecosystems
(Noordwijk et al., 2004; Young, 1997), or bananas (Blomme, 2000a; et al., 2000b;
Chapter 1.4); they seem an appropriate tool to quantify the ‘functional
equilibrium‘ (Swennen, 1984). As the Musa family seems rather sensitive to their
growth environment (Turner et al., 2007; Carr, 2009), we wanted to try whether we
could quantify that relationships. The relations within Musa plants, between fruit
and shoot traits (Carr, 2009), or root and shoot traits (Blomme, 2000a; Swennen,
1984), were already tested (Chapter 1.4 for information), and strong correlations
were once found.
According to Hypothesis 1, shoot-root ratios of Musa plants increase, as the root
biomass is stronger reduced than the shoot biomass under high natural shading
(Chapter 7.2). According to Hypothesis 3, shoot and root traits within Musa plants
are strongly positively correlated (7.1.2). Certain environmental conditions are
correlated to banana root traits (Chapter 7.1.1). Genotypic differences (Musa) are
assumed.
7.1 Relations below- and aboveground
The Musa root traits are inquired for their correlation to environmental parameters
in their immediate surroundings (Chapter 7.1.1), and then root and shoot traits
within banana plants will be correlated (Chapter 7.1.2).
7.1.1 Environmental parameters
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The correlation coefficients (CC) and linear regressions (LR) were computed for
the Musa root content of auger samples (small) and monoliths (large), and the
corresponding environmental measurements (EVP), which involve the soil
moisture (TDR), the leaf area index of the shading canopy (LAI) and analogous,
the diffuse light penetrating beneath the canopy (DIFN). The data were kindly
made available by Erwid Valdivia (Chapter 3.2 for further information). The
monoliths of AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘ and ABB
‘Pelipita‘; and due to several missing LAI/ DIFN measurements, N = 38; N = 42; N
= 38; N = 3035, respectively; and the auger samples of AAA ‘Gros Michel‘ were
subject to the analyses, with N = 210. Three Musa replications were chosen per
natural shade level and cultivar. The root variables root length density (RLD) and
dry biomass per unit of soil (DBU) were decided for. Correlation coefficients are -1
(strongly negative correlated) < 0 (uncorrelated) < 1 (strongly positively
correlated); whereas coefficients of determination are r2 ≤ 0,3 (uncorrelated); ≤ 0,8
(weakly correlated) and ≤ 1(tightly correlated). Independent variable was EVP.
Results
CC are mostly less than -0,18 for TDR (‘Pelipita‘, Tab. 17); are -0,14 to -0,47 for
Tab. 17 Correlation coefficients (CC) for monolith and auger samples in four natural shading levels, between
Musa root content and environmental parameters (EVP), which are TDR, LAI and DIFN. The root variables
chosen are RLD and DBU. In cultivars AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘, ABB ‘Pelipita‘
for monoliths, and AAA ‘Gros Michel‘ for auger samples.
Analysis EVP Root variable
Gros Michel Gros Michel Curraré Morado PelipitaAnalysis EVP Root variable
auger monolithsmonolithsmonolithsmonoliths
CC TDR RLD 0,001 -0,168 -0,042 -0,051 -0,174
DBU 0,060 -0,182 0,057 -0,047 -0,306
LAI RLD -0,142 -0,348 -0,325 -0,144 -0,343
DBU -0,098 -0,250 -0,352 -0,299 -0,467
DIFN RLD 0,121 0,279 0,294 0,335 0,328
DBU 0,069 0,234 0,318 0,411 0,436
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35 Occasionally, ʻscannedʻ and ʻweighedʻ variables were not both missing, if sample lost in lab; all TDR were complete, thus N = 46; N = 46; N = 42; N = 46; N = 230, respectively.
LAI (‘Gros Michel‘ to ‘Pelipita‘), thus being negative, and 0,1 to 0,44 for DIFN
(‘Gros Michel‘ to ‘Pelipita‘), hence being positive. In LR (not shown), r2 develop
naturally similarly, with no r2 > 0,22 in LAI (‘Pelipita‘ and DBU, Fig. 22), no r2 > 0,2
in DIFN (‘Pelipita‘ and DBU), and r2 being often far < 0,09 in TDR. CC and r2 of
auger samples are much smaller than those of ‘Gros Michel‘ monoliths. In DBU, r2
and CC usually exceed those of RLD. To distinguish the dessert bananas and
cooking banana/ plantain is rather difficult, as both groups are occasionally of
lower/ higher CC and r2, thus inconclusive.
Discussion
The EVP, that concern the radiation profile (LAI, DIFN), are weakly correlated to
the Musa root content in samples (Tab. 17; Fig. 22). The LAI is weakly negatively
correlated to Musa roots, thus the density and amount of banana roots declines in
samples, the denser and closed the tree canopy becomes. According to the r2 in
LR, the correlation accounts for not more than 22% of the Musa root content
variation in samples; that is not entirely much. Consequently, the DIFN is weakly
positively correlated to Musa roots, thus the density and amount of banana roots
Fig. 22 Linear regression (LG) for ABB ‘Pelipita‘ root content and LAI (independent variable). The root
variables DBU and RLD were chosen.
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increases in samples, the more light penetrates the tree canopy. The correlation of
this EVP and the Musa roots explains not more than 20% of the variability in Musa
root contents in samples, which is less than by LAI. ‘Gros Michel‘ is worst
correlated to both EVP, not more than 12% of banana root variation explained by
LAI, than the other three cultivars, particularly ‘Pelipita‘. Auger samples of ‘Gros
Michel‘ have < 2% variation explained; possibly their own variability amongst the
samples and plants (Chapter 5.2.1) did not allow a better correlation.
The DIFN quantifies the amount of light, as the LAI quantifies the amount of
shade. The correlations are closer to the radiation profile EVP, than to the
abundance of Erythrina poeppigiana and Coffea arabica roots in samples (Chapter
6.2.2), which is uncorrelated. Thus, a conclusion to find the light deficiency being a
stronger impact upon Musa root formation suggests itself. Possibly in the
moderate shading levels, i.e. minimal and 25%, other factors become more limiting
to Musa root and shoot growth than light (compare Turner et al., 2007; and
Chapter 6.3), therefor the correlations could be stronger, if shading levels of e.g.
50%, 75%, 90% were only studied. Whether LAI or DIFN is better of use for our
purposes is of no importance.
The soil moisture, as we know (Carr, 2009) is of major importance to banana root
growth. However, the TDR here is uncorrelated to the Musa root content in
samples. Not more than 9% of the variability in Musa root density and amount may
be explained by the correlation, and as the CC range around zero, there is no
conclusive picture of negative or positive correlations. As our plants enjoyed very
high rainfall conditions and well structured soils, possibly the low divergences
between values of 37,4 to 42,9 % water content do not cause a analogous root
formation response, to be measured in a conclusive extent; or possibly the slight
possible effect is overlaid by either the light deficiency or the root competition
effects.
The apparently better correlation of DBU to EVP than RLD to EVP is unexpected,
as fine roots are said to be most reactive to local stimulants, and they mainly
influence the length-dependent root variables, than the biomass-dependent ones.
111
But a stronger decline of DBU caused by any radiation profile change was already
observed in Chapter 6.1, because the whole root system is affected.
7.1.2 Plant parameters
The correlation coefficients (CC) and linear regressions (LR) were done for the
Musa root content of auger samples (small) and monoliths (large), and the
corresponding plant (above-ground) parameters (PP), which are the pseudostem-
height (PSH), the pseudostem-diameter at 1 m height (DIA) and the number of
sucker visible above the soil ground (SU), which were gained by me; and the dry
biomass of the pseudostem (PSDW), the mother corm (the ‘true stem‘ is shoot, not
root biomass; CODW), the suckers (including their corms; SUDW) and the whole
plant (excluding any roots; PLADW), which were kindly made available by Erwid
Valdivia (Annex F). The monoliths of AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB
‘Curraré‘ and ABB ‘Pelipita‘, thus N = 46; N = 46; N = 42; N = 4636; respectively;
and the auger samples of AAA ‘Gros Michel‘ were subdued to the analyses, with N
= 230. Three Musa replications were chosen per natural shade level and cultivar.
The root variables root length density (RLD) and dry biomass per unit of soil (DBU)
were chosen. Correlation coefficients are -1 (strongly negative correlated) < 0
(uncorrelated) < 1 (strongly positively correlated); whereas coefficients of
determination are r2 ≤ 0,3 (uncorrelated); ≤ 0,8 (weakly correlated) and ≤ 1(tightly
correlated). Independent variable was PP.
Results
CC are without exception positive for all PP (Tab. 18). Auger samples (‘Gros
Michel‘) have CC < 0,13 for the biomass-PP (PSDW, CODW, SUDW, PLADW),
and CC > 0,13 for measured-PP (PSH, DIA, SU). r2 of LR are < 0,04 (RLD in SU;
measured-PP); those of biomass-PP are far less than 0,02. The measured-PP are
mainly CC of 0,2-0,5 in monoliths, thus exceeded by CC of biomass-PP with
0,2-0,6. In LR (not shown), r2 develop naturally similarly, having in measured-PP
112
36 Occasionally, ʻscannedʻ and ʻweighedʻ variables were not both missing, if sample lost in lab; in ʻPelipitaʻ, PLADW and SUDW are missing for plant 46 (thus -4 samples).
Tab. 18 Correlation coefficients (CC) for monolith and auger samples in four natural shading levels, between
Musa root content and plant parameters (PP), which are PSH, DIA, SU; PSDW, CODW, SUDW, PLADW. The
root variables chosen are RLD and DBU. In cultivars AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘,
ABB ‘Pelipita‘ for monoliths, and AAA ‘Gros Michel‘ for auger samples.
Analysis PP Root variable
Gros Michel Gros Michel Curraré Morado PelipitaAnalysis PP Root variable
auger monolithsmonolithsmonolithsmonoliths
CC PSH RLD 0,166 0,382 0,284 n.a. 0,302
DBU 0,150 0,135 0,415 n.a. 0,477
DIA RLD 0,155 0,464 0,284 n.a. 0,338
DBU 0,127 0,267 0,425 n.a. 0,536
SU RLD 0,198 0,172 0,201 n.a. 0,370
DBU 0,194 0,031 0,408 n.a. 0,472
PSDW RLD 0,113 0,516 0,225 0,378 0,352
DBU 0,074 0,334 0,404 0,509 0,531
CODW RLD 0,134 0,463 0,300 0,311 0,375
DBU 0,103 0,297 0,432 0,374 0,555
SUDW RLD 0,124 0,348 0,210 0,434 0,402
DBU 0,082 0,238 0,338 0,625 0,607
PLADW RLD 0,125 0,464 0,242 0,378 0,380
DBU 0,086 0,304 0,401 0,509 0,608
0,02 (‘Gros Michel‘) to 0,29 (‘Pelipita‘); and in biomass-PP 0,06 (‘Gros Michel‘) to
0,37 (Fig. 23). CC are higher for DBU, than for RLD, except in ‘Gros Michel‘; that
is analogous for r2 in LR.
Discussion
The above-ground PP are weakly (those measured at the shoot) to moderately
(dry biomass of plant organs) positively correlated to the root traits of Musa plants
(Tab. 18); thus, the root density and amount of Musa root content in samples
increases simultaneously as the plants become thicker, taller and heavier (larger in
terms of dry biomass). In ‘Pelipita‘, e.g., PSH accounts for 23% of variability in root
contents in the samples (r2 of LR), whereas DIA accounts for 29% and PLADW for
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37% (Fig. 23). There is less divergence amongst PSH and PSDW (‘Pelipita‘: 28%),
naturally; in ‘Curraré‘, CC of 0,4 (PSDW to DBU), or CC of 0,42 (PSH to DBU). In
‘Curraré‘, the divergence amongst measured-PP and biomass-PP is generally
small (both max. 22% of variation in Musa roots explained). The picture drawn by
CC and r2 of LR is quite uniform, anyway.
The measured-PP may only account for less variability in Musa roots - i.e. 15-30%
- than the biomass-PP, which may explain 15-40% (r2 in LR). That is quite a pity,
as the non-destructive, alternative sampling methods would only involve such
traits, that can be measured without ‘harvesting‘ the whole plant. The dry biomass
of the shoot only is measurable after doing so. Tight correlations as found by
Blomme (2000a), could not be confirmed. At any rate, the DBU being in most
cultivars better correlated to shoot traits than the RLD. That seems rather logical
here than for EVP-correlations (Chapter 7.1.1), in which the RLD was expected to
react to local stimulants like soil moisture. Apparently, biomass traits should be
referred to, when changes within the plants are to be quantified; the ‘functional
equilibrium‘ of a plant (between shoot and root) may be better assessed by
biomass comparisons. Possibly root-length could be better related to leaf area, as
Fig. 23 Linear regressions (LR) for AAB ‘Pelipita‘ root content and PLADW (independent variable). The root
variables DBU and RLD were chosen.
114
both are the ‘functional traits‘ of growth resource acquisition. Another possibility
would be, that the shoot- and root traits generally are not proportional related in all
four shading levels (compare Chapter 7.1.1), because of diverse and varying
impacts upon the Musa experimental plants. Another possibility to evaluate the
biomass changes due to each shade level will be tried in Chapter 7.2. Anyhow, the
shoot trait correlations are closer (moderate) than both the ‘other‘ root correlations
(Chapter 6.2.2) and the EVP-correlations (Chapter 7.1.1), thus it suggests itself
that a shift in the plants ‘functional equilibrium‘ may be the major cause of declined
Musa root contents in 75% shade.
The best correlated measured shoot traits seems to be DIA, with 18-29%
explained variability in Musa roots (all cultivars); yet, the correlation is weak. DIA
was beforehand used well (Blomme, 2000a; et al., 2000b). In biomass-traits, the
best correlation varies due to the Musa genotype studied: PSDW explains 27% of
‘Gros Michel‘ monoliths (RLD); SUDW 40% of ‘Morado‘; CODW 19% of
‘Curraré‘ (not much divergence to others), and PLADW 37% of ‘Pelipita‘ (all DBU).
Genotypic variation is visible in A. the PP which are best correlated, and B. the
magnitude of the correlation. Distinguish the correlations by dessert bananas or
cooking banana/ plantain seems not conclusive. The auger samples generally only
explain about 2-4% of variation in ‘Gros Michel‘ root formation. Possibly the auger
samples do not represent an entire individual root system so balanced as
monoliths, who definitely seem to succeed in this task. Possibly the sucker
formation (Chapter 5.1.2) influenced that purpose strongly.
7.2 Shoot-root ratios
The shoot and root biomass may be compared in how their ‘functional equilibrium‘
changes under natural shading in different levels. Both biomass compounds are
possibly intensively correlated.
The shoot : root ratios (SRR) were computed by dividing the total shoot dry
biomass (PLADW; including the corms and suckers) by the total root dry biomass
115
(TRB-dry), that was estimated out of the soil cores (Chapter 6.3 for further
information; Fig. 20 A.). That was done for each Musa plant individually, thus N = 3
per natural shade level and cultivar37. The SRR were developed for AAA ‘Gros
Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘ and ABB ‘Pelipita‘. The dry biomass
of the shoot (PLADW) was kindly made available by Erwid Valdivia.
Results
The SRR is usually highest for minimal shading, except ‘Curraré‘ (Tab. 19). The
SRR are very diverse, but generally, they are lowest for 25% (‘Morado‘, ‘Pelipita‘)
or 50% (‘Gros Michel‘, ‘Curraré‘). For higher natural shade than the just named,
they increase again. For individual Musa plants, the difference amongst plants
within one shade level is as high as (exemplary) 8,13 in minimal and low as 1,89 in
50% shade of ‘Curraré‘ (compare Fig. 24). Usually, minimal shade shows the
strongest divergences amongst plants. Several SRR were exceedingly high, so
that they had to be excluded. Caused by the exceptional low root contents (see
Chapter 6.1.1), 1 monolith of plant 35 (‘Morado‘, 50% shade) is excluded in Tab.
19; it would alter the result considerably; and 1 monolith of plant 24 is excluded in
Tab. 19 (‘Curraré, 75% shade). Not excluded is 1 monolith of plant 28 (‘Curraré‘,
75% shade); an exclusion would cause a SRR of 4,89 which seems far more
convenient. Two plantain plants of ‘Curraré‘ have exceptional low PLADW-values
(Annex F), no. 25 in minimal, and no. 30 in 25% shade. Those excluded would
cause a SRR = 7,51 of minimal and SRR = 5,38 of 25% shade, therefor not alter
Tab. 19 Shoot-root ratios (SRR) of Musa plants computed for four natural shade levels and the Musa cultivars
AAA ‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘ and ABB ‘Pelipita‘. The basis of the SRR is total root
biomass, and dry biomass of both components was used.
Analysis Shade Gros Michel Curraré Morado Pelipita
SRR Minimal 4,66 5,88 17,65 13,54
25 % 3,71 3,98 3,68 3,66
50 % 2,14 2,10 6,18 5,50
75 % 3,03 13,73 6,11 3,58
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37 In ʻPelipitaʻ, PLADW is missing for plant 46 (thus -1 plant in 25% shade; Fig. 24 A.).
the shade levels‘ sequence.
Discussion
According to the SRR shown (Tab. 19), the SRR are most uniform amongst the
four Musa cultivars for 25% natural shading, with 3,66 - 3,98. That means the
shoot biomass (PLADW), including corms and suckers, is approx. four times larger
than the root biomass of the whole banana mat (TRB-dry). That is about half of the
Fig. 24 Shoot-root ratios (SRR) for individual Musa plants in four natural shade levels, for cultivars AAA ‘Gros
Michel (A.) and ABB ‘Pelipita‘ (B.). The basis of the SRR is total root biomass, and dry biomass of both
components was used. 1st replication of ‘Pelipita‘ is missing, as no PLADW was available.
117
B.
A.
SRR measured by Blomme et al. (2000b; in Chapter 1.4 above); but that was not a
shading experiment. Compared to those SRR (Blomme et al., 2000b), the minimal-
shading-SRR from me are lower for ‘Gros Michel‘ (4,2-5,1; Fig. 24 B.) and
‘Curraré‘ (5,88, Tab. 19), but far higher for ‘Morado‘ (17,65, Tab. 19) and
‘Pelipita‘ (11,6-17,7, Fig. 24 A.). Even with the ‘lowest‘ SRR found by us, approx.
3, the bananas have still quite high SRR compared to trees or other in agroforestry
systems used plants (Noordwijk et al., 2004; Young, 1997; Kenzo et al., 2010) or
to express it like that, they become a ‘normal‘ SRR; and considered the other
results, our bananas can have much higher SRR. Given that, the bananas have
generally few root dry biomass compared to high shoot biomass (i.e. high SRR), at
6 months age, we must say (see Chapter 1.4; Blomme et al., 2000b). In course of
maturity, the root mat size will increase further (highest at begin of shooting;
Blomme, 2000a) and through shooting and flowering, the bunch mass will add
considerable shoot biomass.
The individual Musa plants‘ SRR of AAA ‘Gros Michel‘ must be treated carefully, as
the PLADW (shoot) is indeed the corresponding one for each plant, but the TRB-
dry (root) is the average value for each natural shade level given by our estimation
in Chapter 6.3. Therefor possibly, the divergence amongst individual bananas is as
low as 2 within a shade level (75% shade, Fig. 24 B.), which on the contrary may
be ~6-7 (ABB ‘Pelipita‘, minimal shade, Fig. 24 A.). Next to the edaphic conditions,
the canopy closure may be irregular as well, like Siles et al. (2010) indicate and
cause a divergence in plant growth. The SRR in minimal shade, exemplary, is high
by 13,73 for AAB ‘Curraré‘. As no irregularities in particularly low root contents in
the monoliths occurred, a by any means large shoot must be the cause.
The essential question is, how the SRR is composed of PLADW (Annex F), and
TRB-dry (Chapter 6.3). Primarily, the TRB-dry increases in all four cultivars in 25%
shade, which is 184 to 213 g (‘Gros Michel‘), 331 - 1108 g (‘Curraré‘), 262 - 592 g
(‘Morado‘); and 259 - 925 g (‘Pelipita‘). The respective development in PLADW is
less uniform. ‘Gros Michel‘ are the smallest plants (<1 kg), but largest in minimal
shade; ‘Morado‘ and ‘Curraré‘ are equally larger in minimal shade. ‘Pelipita‘, on the
contrary, has smaller plants in minimal shade. Therefor we must conclude, that the
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apparent decline in SRR to 25% shade is caused by a strong root biomass raise
instead of a strong shoot biomass raise. In the then higher shade levels, the TRB-
dry, as known, only declines (to 88 g; 159 g; 93 g; 133 g; respectively). In the
PLADW, equally not more than a decline is to be found. Those declines have to be
more pronounced for roots than shoots, as the SRR generally increase likewise.
The overestimation of the TRB-dry in 50% shade (explanation in Chapter 6.3) had
caused a slightly lower SRR (Tab. 19), than the probably smaller ‘realistic‘ TRB-dry
would have done. This would not alter the conclusion in general, as it is now. By
involving the shoot biomass now, we may evaluate the plant ‘functional
equilibrium‘ and the divergences amongst cultivars in a broader sense now. The
cvs. ‘Gros Michel‘ and ‘Curraré‘ are represented in SRR ~2 in 50% shade. As we
may also find in 75% shade, no distinction according to the genome group could
be done. When we now align several perspectives, a picture may be drawn: When
we analyse the SRR of 75% shade, we find that ‘Gros Michel‘ and ‘Pelipita‘ had
less PLADW (shoot) left, compared to their TRB-dry, than the other two cultivars.
The decline of root contents in monoliths (minimal to 75% shade) was very similar
for the first named cultivars measured by RLD (Chapter 6.1.1 and 6.4). Though,
measured in DBU, in the dessert bananas was 67 and 72% (‘Gros Michel‘ and
‘Morado‘, respectively) and accordingly 58 and 63% (‘Pelipita‘ and ‘Curraré‘). So,
those declines do not explain any SRR development. The general picture though
is maintained, as cv. ‘Morado‘ always had low root amounts, but strong shoots.
Thus, its SRR stay (except 25% shade) >6 (Tab. 19). On the contrary, cv. ‘Gros
Michel‘ had always equal contents of roots (low), but also has small shoots. This is
reflected in SRR <5 (Fig. 24 A.). ‘Pelipita‘ and ‘Curraré‘ surely attracted by their
high TRB-dry, but the divergence in PLADW seems not consistent throughout the
four shade levels (Tab. 19). It appears, as if the composition of plants adapts for
each Musa cultivar in a different magnitude, although equal in its purpose and aim,
caused by the cultivars‘ inherent shoot and root formation characteristics.
At last, we may relate the ultimate influence, our banana plants could experience,
to the calculated SRR-development: the abundance of Erythrina poeppigiana and
Coffea arabica roots in the samples. The slightly higher ‘other‘ root amounts in the
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75% and minimal shade level (Chapter 6.2.1) is to be found precisely in the levels
of higher SRR. Whereas the higher ‘other‘ root amounts are found around the cvs.
AAA ‘Gros Michel and AAB ‘Curraré‘, which have no congruent SRR in 75% shade
and only in 50% both an SRR of ~2. We conclude, that the essential development
in Musa root formation is found in 75% shade (Chapter 6.1) and hence A. there is
no conformity to the respective cultivars in SRR, and B. as considered in Chapter
6.4, the primary effect of light deficiency responses in the plant take place in that
shade intensity, and contrarily, the addition of ‘other‘ roots is this shade intensity
only very poorly pronounced.
We thus may conclude, that both the shoot and root biomass of our Musa plants
are reduced under high natural shade, as suggested by Akinnifesi et al. (2004) and
Blomme (2000a). The ‘functional equilibrium‘ of the bananas (Swennen, 1984) is
shifted towards more shoot biomass. Probably the Musa increase their leaf area to
capture more sunlight, as less radiation penetrates the shade tree canopy
(Noordwijk et al., 2004; Swennen, 1984). At the same time, the authors find, the
smaller plant need less nutrients and water taken up by roots, the root system can
be kept smaller. By this the ‘cost‘ to maintain the ‘transient‘ Musa root system
structures (Draye, 2002) is reduced, as the building of roots is expensive in terms
of invested carbohydrates (Rao et al., 2004; Schroth, 1999).
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7.3 Conclusion
The present Chapter helped us to some important insights into the correlation and
dependence of Musa root formation. The ‘functional plant equilibrium‘ varies due
to its according light portfolio of its surroundings (as suggested by Noordwijk et al.,
2004; Swennen, 1984; Rao et al., 2004; Schroth, 1999), therefor proofed to be a
powerful tool to assess the influences upon the Musa plant changes. The
correlations first were not as good as we hoped (Chapter 1.4: Blomme, 2000a),
but possibly the application to plants subdued to light availability experiments did
not work out; the rate of of changes with the Musa plants probably can not be
concentrated in just one descriptive regression or correlation model. When we put
together the Chapters 6 and 7, it seems at present most likely that the individual
Musa plant equilibria account for the diverse root contents in our samples, which
we observed in moderate natural shade levels (25% and minimal shade; Chapter
6.1); than any major influence by ‘other‘ root abundances, environmental impacts
or even light availability (compare Turner et al., 2007). As said, we conclude, that
the relations within the Musa plants are the essential causes for the effects in root
and shoot formation under high natural shade levels, primarily induced by the low
light availability.
In terms of Hypothesis 1, the shoot-root ratios (SRR) of banana and plantain
decrease to moderate shade levels (SRR ~3,7), by e.g. an increase in root mat dry
biomass. The shoot-root ratios increase for high natural shading again, as the
banana root mat declines stronger than the shoot dry biomass declines. In terms
of Hypothesis 3, measured Musa shoot traits are weakly positively correlated to
root traits (CC < 0,5), the best trait to explain root biomass is the pseudostem
diameter. The Musa shoot dry biomass is moderately correlated to Musa root dry
biomass (with CC < 0,6). The environmental parameters LAI (canopy closure) and
DIFN (diffuse available light) are weakly negatively correlated to Musa root
contents (CC > 0,3 mostly). The environmental measurement TDR (soil moisture)
is uncorrelated to Musa root contents in cores (with r < 0,3).
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8. Conclusions
The hypotheses (Chapter 2) we stated in the beginning of our work, are precisely
answered in the ‘Conclusion‘-Chapters of each part (in Chapter 5.3, 6.4 and 7.3).
The apparently predominating light deficiency as the cause, which influences the
Musa roots rather than any root competition, may particularly be distinguished due
to the excellent growing conditions we found in the Central Highland of Costa
Rica, in Turrialba. “How much root system does a (the) plant need?“ (Noordwijk et
al., 2004; Nair, 1990; Akinnifesi et al., 2004), we asked in the introduction to the
study at hand (Chapter 1.3). In the loamy clayey soil texture, the very high annual
rainfall and despite that, good water drainage in the soil; the non-existent pressure
of infestations of any kind and the apparently fertile enough soil demand the plants
only to form small root systems. According to Blomme (2000a), the root systems
are despite the size able to sufficiently support the respective shoot of the plants;
and as the shoot decreases under high natural shade, the demand sinks
simultaneously. No larger root systems for our crops, than absolutely necessary,
are required. Schaller et al. (2003a) assume in their similar experiments, that due
to a general high availability of growth resources, no competition arises for growth
resources.
This advantageous situation will certainly change in diverse climatic conditions.
The ‘TCI‘ (tree-crop interface) will become larger under less favourable conditions
and a lower offer of growth resources (Young, 1997). More arid seasons and less
fertile soils influence any kind of plant grown and will increase the competition of
the mixed-species system for growth-resources. Root systems possibly have to
get larger (Noordwijk et al., 2004; Carr, 2009). This could depress the yields and
biomass production of all species to a certain level (Schroth, 1999). Schroth
(1999) and Turner et al. (2007) thus admit, that an over-use of growth resources,
such as light, root-space or soil-borne growth resources, has to be avoided. The
authors explain, that productivity naturally will level off at the least available factor.
Beer et al. (1998) sees strong impacts of the site conditions upon the importance
and effect of shading and shade trees; and Siles et al. (2010) observed the coffee
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to be more restricted by shade trees in tropical lowlands. The bananas could be
more competitive in lower, humid regions to coffees.By Schroth (1999), this is to
get to know a certain combination of species and their plasticity in an environment
and climate; development is the interaction of genotype and environment.
Probably the competitive potential of our plots would be higher, if not the basic
growing combination coffees and trees would be older than 35 years. We assume,
the competitive balance could be different in a completely young planted plot
(Akinnifesi et al., 2004; Schroth, 1999). The bananas are supposedly stronger in
competition from their ratoon crops onwards, as they increase in size still
(Robinson and Nel, 1988). Our Musa are generally horizontally spread (Chapter
6.1.2). This form of a root system is commonly inconvenient to a growing system,
in which we count on the segmentation of below- and above-ground space as the
key to success. But Schroth (1999) generally suggests, that a shallow crop may
well fit into systems, if an associated crop is vertically stratified. Very likely, our
Musa plants colonised a left ‘soil gap‘, which the author considers very useful.
A functional system must be the purpose. Yet the radial exploitation of Musa roots
demands space, that a coffee plot sorted by strict rows may not have. An
alternative species‘ arrangement, finally, a newly rearranged combination of Musa
spp., Coffea arabica and Erythrina poeppigiana could do further improvements in
spacing intervals. Exemplary, if the Musa are replaced into the wind sheltered
middles of boundary planted trees and coffee rows, the bananas would have
more, the coffees less radiation. This segmentation of the plot could be beneficial
to the whole system.
At last we may point out, that several methodological errors in our root coring work
are easily inherent to the study and analysis of roots, but may be solved by few
additional effort. This means the common problem of root loss. Muñoz and Beer
(2001) reported studies using even 5 mm grid sieves. Blomme (2000a) found the
root loss generally being to less targeted. When we use < 2mm grid sieves and
choose to sum up the fine roots <1 mm as well, we further could approximate the
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root contents in samples to ‘absolute‘ root densities and particularly assess the
finer roots so conclusive about the relative competitiveness of species.
8.1 Farming improvement
Improvements in crops and arrangements for growth must be of use to smallholder
farmers, in meliorating their performance and sharpen their families living
conditions; land use forms must suit their needs as much as environmental and
technical aspects (Young, 1997). Beer et al. (1998) found farmers to really care for
mid- and long-term perspectives in coffee growth; and Bioversity‘s workshops with
farmers, to exchange practical and scientific knowledge, often find interested and
positive responses from amongst the producers.
Particularly in fields devoted to provide domestic food supply, farm fields often are
less structured and ‘furbished‘, as particularly our experimental plots were. It is
likely, that home garden or tree-garden similar systems inherit broader ranges of
interactive interfaces and complex competitive balances. The fields of a producer
are already established and surely involved in continuous production. Therefor any
improvement may be introduced in long-term changes and management options,
that avoid radical replanting or renewal of an area. Most fortunate in our case, the
restraints in shoots of plants (e.g. light penetrating the canopies of shade trees)
are far easier to control than any root restraints (Schroth, 1999).
We showed in the study at hand, that excessive shading reduces the growth of the
Musa plants, so that such should be avoided by farmers. Moderate shading may
be beneficial in a way for Musa (Turner et al., 2007), and particularly for the coffee,
which is convenient to higher shading (40-70%; Beer et al., 1998). A brighter
radiation portfolio is to be gained by either planting less shade trees, or prune the
shade trees stronger. Both should be realistic measurements. Shade trees that are
of no use, i.e. the scattered ‘Poró‘s‘ in our minimal shade (they provide no useful
amount of shade, but are complete plants with stems and root systems within the
plots) should be eradicated. They require labour, space, growth resources, but
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give no direct returns to the farmer (Schroth, 1999). Shoot pruning has additional
positive effects, as green manure and a reduction of root activity (Schroth, 1999;
Rao et al., 2004; Nair, 1993). At any rate, as much as farmers already grow quite a
number of different Musa cultivars, as much we found no evidence that a particular
cultivar or genome group could not be grown with understory to natural shade.
The remarkable density of our experimental plots did not turn out to be our primary
concern. The bananas require more space than, especially the dwarf variety, the
coffee shrubs, caused by their natural size. As the Musa are likely to get stronger,
from the ratoon crops onwards (Blomme, 2000a; Robinson and Nel, 1988), the
growing system should be observed in this respect. When a wider spacing could
reduce the inter-specific competition and serve a better harvest, they should be
considered, even though the total number of plants decreases. Root competition
was shown manageable successfully by root barriers also, i.e. trenches, plastics
etc.; but as they are costly and laborious, they usually do not form an alternative to
enable other intervals of spacing (Muschler, 1993; Young, 1997). As we have
shown (Chapter 6.1.2), the major roots of Musa concentrate radially around the
plants particularly. Commonly coffee is planted in rows, whereas it seems
advantageous in Musa to admit a radial space around the plants. The particular
horizontal, shallow root mat determines this space to be 80 cm radius. This root
systems may especially be combined with deeper or vertically rooting species in
such a mixed system.
Coring to achieve root mat access seems a plausible alternative to receive an
impression of the momentary root distribution (according to Noordwijk et al., 2004)
in farm fields. The positioning of sample locations and design should be carefully
chosen. To classify the bananas situation, the shoot compound of the plant should
be assessed as well as the root biomass. Anyway, any management suggestions
must be adopted by the producers, or they are not of use (Young, 1997). Lower
yields may cause shortages of food and lower income (Young, 1997), which can
be negatively and should not be entered into light-headed. The diversification of
products, the harvest period or reduced inputs may be beneficial and heave the
benefits beyond the reductions (Siles et al., 2010).
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8.2 Perspective
The general perspective may be, that growing bananas under shade trees may be
possible in certain limitations, and in association with an organic coffee production.
The involvement of such growing systems in the commercial agroforestry of Latin
America attributes a good potential to the system, to improved, maintained and to
be used in future. Despite that, several perspectives could lead to interesting
continuations. The root systems of other plants provide a restriction and influence
to Musa root systems, which cannot be compared one-to-one to impermeable soil
layers, coarser soil textures or any similar edaphic impact. Anyhow, the impact of
other root systems is not to be found in the important proceedings of Turner and
Rosales (2005), not in papers about edaphic sources for root deterioration
(Gauggel et al., 2005; Turner, 2005), nor in the editors‘ recommendations for future
research to complete the knowledge upon banana roots.
The core sampling systems we decided for were centred around the experimental
bananas. A system scattered across a whole plot could help to reclassify the
results in a greater context and determine the multi-species combination at more
possible tree-crop interfaces (compare Schaller et al., 2003a; Siles et al., 2010;
Muñoz and Beer, 2001). As by now the knowing about the Musa in their immediate
vicinity increased, we may expand our view. The path we used to estimate the
total root system proofed to be quite usable. But if the possibility would arise to
recheck the assumptions to several truly in the whole extent measured bananas, it
would help to improve the system (as in Blomme 2000a; Mukasa et al., 2005). The
tree root systems could be studied stronger, like the extent of their nodulation and
N2-fixation, in the case of leguminous trees. A comparison of shoot-root ratios of
different species would give new insights (Akinnifesi et al., 2004); also to conduct
the experiment with younger coffees and trees, and older Musa plants. At last to
transfer the root architecture to root functioning (compare Schroth, 1999).
Upcoming studies could separate their efforts to two paths, starting out at the by
now gathered knowledge. On the one hand, an isolation of specific traits to
observe the effects (Young, 1997); it would be interesting to provide experimental,
126
field grown Musa with artificial shade. Thus the root competing impact could be
excluded and only the light deficiency observed; yet an edaphic surrounding
should be more advantageous to simulate ‘true‘ conditions, than hydroponic
surroundings. On the other hand, the present studies could be matched with ‘on-
farm analogons‘; the trials could be extended to more ‘realistic‘ growing conditions,
and the knowledge we have could be re-checked to confirm it. More environmental
divergences could be assessed and it could be intended to develop standardised
mechanisms and easily-to-adapt practices suggestible to the producers (Schroth,
1999; Nair, 1993).
As the banana root system was defined as “a population of roots of different types
and age that evolve dynamically according to root formation and root senescence
(Draye, 2002)“. Therefor the long-term strategies and dynamics of this growing
system should be monitored (Draye, 2002; Noordwijk et al., 2004). Muñoz and
Beer (2001) suggest for a system of a simultaneous agroforestry kind to time the
root activity of each of the species in a sequential way. Models for root
development were developed for some time now (Noordwijk et al., 2004), and
some extended to banana roots (Draye et al., 2005: ‘virtual coring‘). At last, the
harvest components could be observed in a longer trial. We did conclude from the
shoot biomass to a development of bunch masses, but a quantification and
possible correlations to root traits could be very interesting.
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9. Annex
Annex A List of all Tables
Tab. 1 Components of the Musa root system (Araya, 2005; Swennen et al., 1988) .........21Tab. 2 Root and shoot traits (Musa) correlated (Blomme, 2000a) .........32Tab. 3 Monthly meteorological data in Turrialba (CATIE) .........39Tab. 4 Musa plants measurements in three cultivars .........42Tab. 5 Light conditions in four natural shade levels (data: Erwid Valdivia) .........43Tab. 6 Soil texture in the experimental plots .........44Tab. 7 Soil analyses in the experimental fields .........45Tab. 8 Soil humidity measured by TDR (data: Erwid Valdivia) .........45Tab. 9 Basic information on monolith and auger sample methods .........50Tab. 10 System implemented for coarse tree root scans .........53Tab. 11 AAA ‘Gros Michel‘ root contents in auger: DB, RLD .........61Tab. 12 Optimal sampling intensities calculated .........71Tab. 13 Root contents of Musa in monoliths: VOL, SRL .........78Tab. 14 AAA ‘Gros Michel‘ root contents in auger: SRL .........86Tab. 15 Correlations of Musa root to ‘other‘ root contents .........96Tab. 16 Total root system estimated for four Musa cultivars .......100Tab. 17 Correlations of Musa root contents to environmental parameters .......109Tab. 18 Correlations of Musa root contents to plant parameters .......113Tab. 19 Shoot-root ratios of Musa plants .......116
Annex D Post-Hoc tests for shade levels and cultivars in monoliths .......131Annex E A. Post-Hoc tests of ‘other‘ roots in monoliths .......132 B. Post-Hoc tests of ‘other‘ roots in auger samples .......133Annex F Shoot dry biomass of Musa (data: Erwid Valdivia) .......134
128
Annex B List of all Figures
Fig. 0 Banana yield response to shade (Turner et al., 2007) .........17Fig. 1 Net CO2 assimilation of AAA ‘Gros Michel‘ (Schaffer et al., 1996) .........18Fig. 2 Growth and decay of roots of perennials, annuals (Noordwijk et al., 2004) .........24Fig. 3 Biomass components of Musa plants (Blomme et al., 2000b) .........34Fig. 4 Soil coring method after Blomme (2000a) for Musa plants .........35Fig. 5 Four shade levels in ‘La Molina‘ .........40Fig. 6 Basic planting scheme of Musa and Coffea arabica .........41Fig. 7 Root sampling tools of monolith and auger method .........47Fig. 8 Design of monolith and auger sample positions .........49Fig. 9 Disturbances in auger (core height) and monoliths (surface) .........58Fig. 10 Scanner images acquired in two cases .........59Fig. 11 Root system traits: sucker and root axes .........60Fig. 12 Improvement of soil coring methods .........64Fig. 13 %SE/M of AAA ‘Gros Michel‘ in monoliths and auger samples .........67Fig. 14 Sampling intensities for monoliths and auger samples .........70Fig. 15 Root content of Musa in monoliths: RLD, DBU .........79Fig. 16 AAA ‘Gros Michel‘ root contents in auger samples: RLD .........85Fig. 17 Root contents of ‘other‘ roots: RLD .........92Fig. 18 Two auger samples described at 40cm-sample-position .........98Fig. 19 The ‘pyramid figure‘ of an enlarged auger sample set .........99Fig. 20 TRV and TRB-dry for four Musa cultivars .......101Fig. 21 TRS in DB of AAA ‘Gros Michel‘ in sample distances .......102Fig. 22 Linear regression of LAI and AAB ‘Pelipita‘ .......110Fig. 23 Linear regression of PLADW and AAB ‘Pelipita‘ .......114Fig. 24 SRR of individual AAA ‘Gros Michel‘ and AAB ‘Pelipita‘ .......117
129
Annex C Abbreviations
CC correlation coefficientCODW mother corm dry weight [g]CR coffee-row (direction: in line Musa - next coffee)DB root dry biomass [g]DBU root dry biomass per unit of soil [g dm-3]DIA diameter of pseudostem at 1m height [cm]DIFN diffuse light (beneath the tree canopy) [non-dimensional]EVP environmental parametersFW root fresh weight [g]GLM General Linear ModelIR inter-row (direction: in line Musa - next Musa)LAI leaf area index (shade trees) [cm2 cm-2]LEN root length [cm]LR linear regressionMANOVA multivariate analysis of variance%M/TRS % one monolith/ total root systemPA root project area [cm2]PLADW plant dry weight (shoot, including corm) [g]PP plant parameters (shoot)PSDW pseudostem dry weight [g]PSH pseudostem height [cm]RLD root length density [cm cm-3]SA root surface area [cm2]SE standard error%SE/M % standard error/ average meanSRL specific root length [cm g-1]SRR shoot-root ratioSU number of visible sucker above ground surfaceSUDW suckers dry weight (including corms) [g]TDR soil humidity (time domain reflectometry method) [%]TRB-dry total root biomass dry [g]TRB-fresh total root biomass fresh [kg]TRS total root systemTRV total root volume [cm3]TRL total root length [m]VOL root volume [cm3]
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Annex D Post-Hoc tests for shade, cultivar in monoliths (Chapter 6.1.1)
Post-Hoc test by Tukey-HSD in SPSS, for factors shade level and cultivar in the monoliths sampling method.
Homogenous subgroups are shown, with average mean values for groups. Root variables DBU and RLD were
chosen. As group-sizes differed, the homogenous average was used, which is N = 44,93/ 44,92. Alpha = 0,05.
N
DBUDBUDBU RLDRLD
N Sub-group
1
Sub-group
2
Sub-group
3
Sub-group 1
Sub-group 2
Shade level
Cultivar
75 % 42 0,044 75 % 0,017
50 % 47 0,090 50 % 0,025 0,025
Minimal 45 0,125 0,125 25 % 0,031
25 % 46 0,138 Minimal 0,031
Sign. 1,000 0,186 0,882 Sign. 0,132 0,425
Gros Michel 46 0,058 0,019
Morado 42 0,091 0,091 0,023
Pelipita 46 0,114 0,114 0,027
Curraré 46 0,137 0,034
Sig. 0,242 0,561 0,553 0,058 1,000
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Annex E Post-Hoc tests for Erythrina poeppigiana and Coffea arabica root
content in monoliths and auger samples (Chapter 6.2.1)
A. Post-Hoc test by Tukey-HSD in SPSS, for Coffea arabica and Erythrina poeppigiana root content for four
shade levels and vicinity to Musa cultivars in monoliths. Homogenous subgroups are shown, with average
mean values for groups. Root variable RLD and DBU were chosen. As group-sizes differed, the homogenous
average was used, which is N = 45,154 (shade) and N = 45,165 (Musa cultivar). Alpha = 0,05.
NRLDRLD DBUDBU
N Subgroup 1
Subgroup 2
Subgroup 1
Subgroup 2
Shade level
Vicinity of Musa cultivar
50 % 47 0,038 25 % 0,802
25 % 47 0,038 50 % 0,820
75 % 42 0,043 0,043 Minimal 0,984
Minimal shade 45 0,056 75 % 1,222
Sig. 0,784 0,065 Sign. 0,342
Pelipita 46 0,034 0,601
Morado 42 0,038 0,682
Gros Michel 46 0,05 1,109 1,109
Curraré 47 0,052 1,373
Sig. 0,354 0,653 0,184 0,721
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B. Post-Hoc test by Tukey-HSD in SPSS, for Coffea arabica and Erythrina poeppigiana root content for four
‘directions‘ from the experimental banana plants and ‘distances‘ of sampling positions in auger samples,
around Musa cultivar AAA ‘Gros Michel‘. The root variables RLD and DBU were chosen; homogenous
subgroups are shown, with average mean values for groups. As group-sizes differed, the homogenous
average was used, which is N = 67,869 (distance) and N = 56,738 (direction). Alpha = 0,05.
NRLDRLD DBUDBU
N Subgroup 1
Subgroup 2
Subgroup 1
Subgroup 2
Directions of Musa plant
Distance of Musa plant
IR left 58 0,10 IR right 1,58
IR right 57 0,11 IR left 1,72
CR above 56 0,13 CR above 1,80
CR below 56 0,14 CR below 1,89
Sig. 0,245
40 cm 90 0,10 40 cm 1,43
80 cm 92 0,12 120 cm 1,94
120 cm 45 0,16 80 cm 1,96
Sig. 0,066 1,000 0,563
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Annex F Shoot dry biomass of experimental Musa plants
The shoot dry biomass (PLADW) in [g] of experimental Musa plants for four shade levels and four cultivars.
PLADW includes pseudostem, foliage, corms, suckers; but no root axes or lateral roots. The cultivars AAA
‘Gros Michel‘, AAA ‘Red‘ (‘Morado‘), AAB ‘Curraré‘ and ABB ‘Pelipita‘ are given. In italics: exceptional values.
Data kindly made available by Erwid Valdivia.
Replication 1Replication 1 Replication 2Replication 2 Replication 3Replication 3
Plant No. PLADW Plant No. PLADW Plant No. PLADW
Gros Michel
Curraré
Morado
Pelipita
Minimal 1 873,4 5 766,5 9 939,5
25 % 2 961,3 6 670,4 10 742,7
50 % 3 854,2 7 589,7 11 456,6
75 % 4 365,1 8 245,6 12 188,9
Minimal 21 1916,8 25 347,4 29 3293,9
25 % 22 1222,1 26 2519,8 30 484,6
50 % 23 529,9 27 561,0 31 1160,6
75 % 24 211,9 28 319,9 32 297,5
Minimal 33 1802,9 37 2813,3 41 2356,0
25 % 34 1959,4 38 2298,1 42 1449,7
50 % 35 1158,4 39 1798,5 43 942,4
75 % 36 397,4 40 446,7 44 218,5
Minimal 45 2632,9 49 2743,4 53 2744,5
25 % 46 n.a. 50 2815,9 54 3168,2
50 % 47 1321,6 51 1653,6 55 1195,3
75 % 48 266,3 52 315,0 56 524,1
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10. References
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