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Violace Putri
MSc Thesis Plant Production Systems (PPS)
January 2015
Oil Palm (Elaeis guineensis) Root Growth in Response to Different Fertilization Practices
Oil Palm (Elaeis guineensis) Root Growth in Response to
Different Fertilization Practices Violace Putri
MSc Thesis Plant Production System
PPS-80436
January 2015
Supervisors:
Maja Slingerland
Lotte Woittiez
Examiners:
Maja Slingerland
Jochem Evers
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Acknowledgements I would like to express my sincere gratitude to everyone who supported me during my thesis process. First and foremost to both of my supervisors, Maja Slingerland and Lotte Woittiez for their supports and encouragements. Secondly, I would like to acknowledge THE UNIVERSITY OF JAMBI that allowed me to use their facilities during my fieldwork. Thank you to all staffs and students that were very helpful since the beginning and were very kind to help me. My appreciation to the PPS group that made me work conveniently. I also want to thanks farmers in Kumpeh for their hospitality and curiosity. Special thanks to my family and my significant one that keep supporting me through my up and down during this thesis process. Thanks to a group of MOA students that transformed a lunch time to a valuable time worth to wait in between hours of working in front of the computer, may our paths cross again in the future. Wageningen, January 2015 Violace Putri
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Table of Contents Acknowledgements .................................................................................................................................. i Table of Contents..................................................................................................................................... iii List of Figures ........................................................................................................................................... iv
List of Tables .............................................................................................................................................. v
Summary ...................................................................................................................................................... 1
1 Introduction ........................................................................................................................................ 3
1.1 Background ................................................................................................................................. 3
1.2 Literature review ...................................................................................................................... 4
1.3 Problem statements ................................................................................................................. 8
1.4 Research Questions and Hypotheses ............................................................................... 8
2 Material and Methods .................................................................................................................. 11
2.1 Study Site .................................................................................................................................... 11
2.2 Experimental Design and sampling locations ............................................................ 11
2.3 Root sampling ........................................................................................................................... 13
2.4 Ingrowth method .................................................................................................................... 14
2.5 Root Measurement ................................................................................................................. 15
2.6 Statistical Analysis .................................................................................................................. 16
3 Results ................................................................................................................................................ 19
3.1 Root Length Density (RLD), Root Dry Matter (RDM) and Specific Root Length (SRL) at different soil zones ......................................................................................... 19
3.2 Root distribution at different soil depths ..................................................................... 21
3.3 RLD, RDM and SRL in different plots ............................................................................. 22
3.4 RLD, RDM and SRL in different fields............................................................................. 24
3.5 Ingrowth bag ............................................................................................................................. 25
4 Discussion ......................................................................................................................................... 27
4.1 RLD, RDM, and SRL in different zones ........................................................................... 27
4.2 RLD, RDM, and SRL at different soil depth .................................................................. 28
4.3 RLD, RDM and SRL under different management practices ................................ 29
4.4 Ingrowth bag ............................................................................................................................. 30
4.5 Recommendation for further study ................................................................................ 31
5 Concluding Remarks .................................................................................................................... 33
References ................................................................................................................................................ 35
Appendixes .............................................................................................................................................. 39
Appendix I. Root Classification to distinguish primary, secondary and fine roots from root samples (Fairhurst, 1996) ....................................................................................... 39
Appendix II. Data and Statistical Analysis Results ............................................................. 40
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List of Figures
Figure 1. Oil palm plantation with pruned leaves under the trunk (a) and without any plants on the ground (b) .............................................................................. 4
Figure 2. Root system on a 10 year old oil palm ........................................................................... 5
Figure 3. Experimental set up and sampling locations ........................................................... 12
Figure 4. Sampling locations in each selected tree ................................................................... 13
Figure 5. Single root auger .................................................................................................................. 14
Figure 6. Washed roots (a) and the intersection method using 1cm x 1cm paper grid to calculate root length (b) ......................................................................... 16
Figure 7. Root length density at different soil zones for different root classes of 12 years old oil palm tree ................................................................................................... 19
Figure 8. Root dry matter at different soil zones for different root classes .................. 20
Figure 9. Specific root length of different root classes in different soil zone. ............... 20
Figure 10. Root length density (a) primary (b) secondary and (c) fine roots of 12 years old oil palm tree at different soil depths ................................................... 21
Figure 11. Root Dry Matter (a) primary (b) secondary and (c) fine root of 12 years old oil palm tree at different soil depths ......................................................... 22
Figure 12. Specific Root length (SRL) (a) primary (b) secondary and (c) fine root of 12 years old oil palm tree at different soil depths .................................... 22
Figure 13. Comparison of RLD in BMP and REF plots in each soil zone.......................... 23
Figure 14. Comparison of RDM in BMP and REF plots at different soil zones .............. 23
Figure 15. Specific root length in BMP and REF plots at different soil zones ............... 23
Figure 16. Comparison of RLD between good and poor managed fields at different soil zones. Bars represent standard error of mean ............................. 24
Figure 17. Comparison of RDM between Good and Poor managed fields at different soil zones. Bars represent standard error of mean ............................. 24
Figure 18. Specific root length density in differently managed fields per root class. Bars represent standard error of mean ........................................................... 25
Figure 19. Root length density (a) and root dry matter (b) in fertilizer and control ingrowth bags. ......................................................................................................... 25
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List of Tables
Table 1. Different management practices between two fields2 .......................................... 12
Table 2. Statistical analysis arrangement to compare roots parameters at different soil zones ................................................................................................................ 16
Table 3. Statistical analysis arrangement to compare roots parameters at different soil depths .............................................................................................................. 16
Table 4. Statistical analysis arrangement to compare roots parameters at different plots .......................................................................................................................... 17
Table 5. Statistical analysis arrangement to compare roots parameters at different fields ......................................................................................................................... 17
Table 6. The contribution of each root class to total root length density (RLD) and total Root Dry matter (RDM) per cm3 in 12 years old oil palm tree at circle zone (n=24) and frond stack (n =24 ) zone. ............................................. 20
Table 7. Group Statistics for RLD, RDM and SRL at different soil zones ......................... 40
Table 8. Paired t-test results at different soil zones ................................................................. 40
Table 9. Group Statistics of RLD, RDM and SRL at different soil depth ........................... 41
Table 10. Paired t-test results for RLD, RDM and SRL at different soil depths ............ 42
Table 11. Statistics of RLD, RDM and SRL at different plots ................................................. 43
Table 12. Independent T-test results between BMP and REF plots at different soil zones ................................................................................................................................... 44
Table 13. Group Statistic of RLD, RDM and SRL at different fields .................................... 45
Table 14. Independent T-test result of different between good and poor fields at different soil zones ........................................................................................................... 46
Table 15. Statistic of RLD and RDM between control and fertilizer treatment in ingrowth study ........................................................................................................................ 47
Table 16. Independent T-test results between control and fertilizer treatment in ingrowth study ................................................................................................................... 47
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Summary Studying oil palm root distribution, especially the distribution of fine roots, and its response to different management practices could give a better management approach for the oil palm plantation, particularly for the efficiency of fertilizer application. The aim of our study was to observe root distribution of oil palm in response to short term change of nutrient availability caused by change in fertilizer application as well as the differences caused by long-term management. The root assessment was conducted on 12 years old oil palm in Ramin village, Kumpeh District, Jambi Province, Indonesia. Two different fields were assessed; the previously poorly managed and better managed fields. Two plots were established in each field, one with best management practice (BMP plot) and the other one continue with their practice as reference (REF) plot. Auger sampling method was used to assess oil palm root distribution at different zones (circle and frond stack zones), and different depths (0-15cm and 15-30cm) on those different plots. Root length density (RLD), root dry matter (RDM) and specific root length (SRL) were calculated and compared for different root classes (primary, secondary and fine roots). Ingrowth method was used to see the differences of root growth between the soil with more nutrient availability and the current soil The results show that the RLD and RDM in the circle zone were higher than in frond stack zone for all root classes except for RLD of fine roots. Both RLD and RDM are also higher in the first 15cm soil depth compare with 15-30cm depths in frond stack zone. Conversely for SRL value, it was significantly higher in frond stack for secondary and fine roots but not for primary roots. The SRL values were the same between roots in 0-15cm and 15-30cm depths except for secondary roots in the frond stack zone. The differences between BMP and REF plots were only significant in secondary roots (both for RLD and RDM) in frond stack zone, but the SRL for all root classes in REF plot were significantly higher than BMP plot for roots in the frond stack zone. No differences were observed between good and poor managed fields. Additionally also no significant differences were observed between roots in fertilized ingrowth bag and control ingrowth bag. The results confirmed that oil palm root density decrease with distance from the tree as well as with depth of soil except for the fine roots that have similar density between the circle and the frond stack zone at the first 30cm soil depth. This result suggests that for the adult oil palm tree, the area outside the circle zone is as important as circle zone for root’s water and nutrients uptake. Higher SRL of fine roots in the REF plot suggests higher plasticity of fine roots in the reference plots but could also suggest that fine roots in the BMP plots has higher biomass per cm root length as a response to chemical fertilizer application Keywords: root distribution, root length density, root dry matter, specific root length, best management practice
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1 Introduction
1.1 Background Palm oil production in Indonesia gains much and more global attention mainly because of its environmental issues. Establishment of new plantations was destroying rainforest area in the country and led to loss in biodiversity and carbon stock (Lee et al., 2014, McCarthy et al., 2012). However, the increase in palm oil global demand and its economic attractiveness ensure the increase of palm oil production in the future (Tan et al., 2009, Wicke et al., 2011). Indonesia is supplying roughly 45% of the global demand (FAOSTAT, 2013) where more than 40% of the plantations are owned by smallholder farmers (BPS-Statistics Indonesia, 2013). Even though the smallholder farmers account for more than 40% of oil palm plantations, their productions only contribute 30% to total palm oil production in Indonesia (World Bank, 2010), suggesting that their production is below private and state owned plantations and far below the optimum yield. Intensification, especially in the smallholder’s plantations can be an option to meet palm oil global demand without further forest encroachment. Increase in oil palm (Elaeis guineensis) production can be achieved through closing the gap between actual yield and potential yield by doing best management practice (BMP). The BMP is a management approach to reduce the yield gap that caused by incorrect assessment of nutrient needs and inefficient management of the mature trees (Donough et al., 2010). Thus this concept can be applied in the existing mature plantations. In BMP concept, inputs and resources are used efficiently based on the evident needs of the plantation, therefore it also minimizes the negative impacts to the environment (Donough et al., 2009). Some studies on BMP implementation in oil palm plantations in Indonesia show that these practices could significantly reduce yield gap (Donough et al., 2009, Rhebergen, 2012, Donough et al., 2010); however, the results vary between areas because of the site-specific nature of BMP (Rhebergen, 2012). “The Best” approach is not always affordable or easy to be implemented by smallholder farmers. Therefore “Better Management Practices” is another approach that improves current practices to increase productivity in affordable way and easy to follow by smallholder farmers. Currently oil palm smallholder farmers, do not have good management in their plantation. The application of fertilizers are not based on what needed by the plant, therefore many nutrient deficiency symptoms are clearly visible in the trees. Most of farmers do not have harvest paths and weeded circles (a clear area around the trunk) that are very useful to reduce yield loss during harvest time. Some farmers even stacked the pruned leaves on the weeded circle or blankly sprayed all ground plants in the plantation (Figure 1a and Figure 1b).Farmers usually harvest every 15 days and they identified the ripe fruits by looking the bunches on the tree, instead of checking the loose fruits in the weeded, resulted high amount of unripe fruits in the harvest. In better management practices (BMP), those mistakes were corrected. Farmers established weeded circles and harvest paths, pruned the leaves and stacked them in the line between trees and in inter-row, do selective weeding,
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harvesting every 10 days and checking the ripeness of the bunch by looking down to find loose fruits in the weeded circle.
Figure 1. Oil palm plantation with pruned leaves under the trunk (a) and without any plant on the
ground (b)
It is difficult to directly see the effect of different management practices to the increase of productivity in the short time because there is a large time lag between stress occurrence or reduction, including nutrient availability in the soil, and yield response. It takes 35-40 months from the initiation of leaf to the ripeness of fruits, and 15 months from the first spikelet initiation (Kramer and Boyer, 1995). Corley (1976) and Turner (1977) found a time lag ranging from 17 to 26 months between stress occurrence and the palm yield response (cited in (Corley and Tinker, 2003b). The effect of improved management on root development might be much faster since oil palm roots grow with a rate of 1.5-3 mm/day for primary roots and 0.3-0.8 mm/day for tertiary roots (Henson and Chai, 1997, Jourdan and Rey, 1997). Therefore the assessment of root development might become an alternative to see the effect of changed management practices on oil palm growth. The assessment of root distribution could give an insight to the ability of roots to capture available resources. In regards to BMP, it could improve fertilizer application so the roots can capture available nutrients optimally.
1.2 Literature review
Oil palm roots are categorized into primary, secondary, tertiary and quaternary roots (Figure 2). The architecture of oil palm roots was explained by Purvis (1956) and Jourdan and Rey (1997). The primary roots (RI) grow vertically downward (RI VD) and horizontally outward (RI H) from the tree base with the main function as anchorage but also possible to absorb water through its unlignified tips (Purvis, 1956, Jourdan and Rey, 1997). The primary roots has a diameter ranging from 5 to 10mm with the length of non-lignified part not more than 3-4 cm (Purvis, 1956). The secondary roots grow horizontally (RII H) from the vertical primary, and grow vertically upward (RII VU) and downward (RII VD) from horizontal primary. The secondary roots have slow rate of lignification compare to primary roots with 5-6 cm of unlignified root tip. The tertiary roots (RIII) branch from secondary roots up to 20 cm in length with the diameter of 0.5-1.5 mm and 2-3 cm of unlignified tip. The quaternary (RIV) roots that are mostly unlignified develop in a large number from tertiary roots with only 0.2–0.5 mm in diameter and no more than 3cm length (Purvis, 1956, Jourdan and Rey, 1997). The absorption of nutrients happen through unlignified part of the root and quaternary roots play main part because of its large
a) b)
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numbers. The growth rates of primary, secondary and tertiary roots of oil palm are 1.5-3 mm/day, 0.75-2 mm/day and 0.3-0.8mm/day respectively (Henson and Chai, 1997, Jourdan and Rey, 1997).
Figure 2. Root system on a 10 year old oil palm (Jourdan and Rey, 1997). The code for roots are RI:
primary; RII: Secondary; sRIII: surface tertiary; dRIII= deep down tertiary; RIV: quaternary; H:Horizontal, VU: vertical upward, VD: vertical downward
Oil palm roots for all classes of roots are concentrated in the top 60 cm of the soil and reduce with distance from the tree. However, the exact concentration of oil palm roots at different soil depths differs based on soil physical properties (Chan, 1977). Oil palm root could grow with only 1 m rooting depth if it can get all water and nutrients required from that area, and on the other hand, the roots can reach more than 5 m depth where water availability is limited (Corley and Tinker, 2003a). In adult oil palms the total dry weigh of absorbing roots increases after 2m from the tree base until radius of 3.5 - 4.5m (Ruer, 1967, cited in (Corley and Tinker, 2003a). Nutrients absorption mostly happens through the fine roots (tertiary and quaternary) which are most abundant in the top 30 cm of the soil (Corley and Tinker, 2003a, Henson and Chai, 1997) Root length, root diameter and root grow rate are some parameters of oil palms that are affected by growing conditions such as differences in soil properties as results of different management practices (Atkinson and Dawson, 2000). It is expected that the nutrient availability has an effect on the development of root system since the main functions of the root are for acquisition of water and nutrients (Hutchings and John, 2003, Sattelmacher et al., 1993). However water and nutrients are not distributed uniformly in the field, and roots have a tendency to concentrate in the soil areas that have abundant resources (Hutchings and John, 2003, Fairhurst, 1996, Hodge, 2004, Kheong et al., 2010, Ostertag, 2001). Additionally, the magnitude of root response to the nutrient availability is not
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uniform across species, and even within species (Hodge, 2004). The relationship between root growth and nutrient availability can be examined in two ways: in response to long term conditions or natural fertility gradients, and in response to short-term changes in nutrient availability because of fertilizer application (Ostertag, 2001). When fertilizers are applied, the root response to the sudden change in nutrient availability will probably differ between plants that were in infertile soil and plants in fertile soil. Plants that are in infertile soil invested more to the growth of its roots in order to acquire more nutrients, and when the nutrients availability increase, the relative allocation to root growth decreases (Ostertag, 2001, Reynolds and D'antonio, 1996). The general pattern is the ratio of root mass to total plan mass (root weight ratio) decreases with increase of nitrogen availability and plant appears to have inverse relationship between root biomass and nutrient availability (Ostertag, 2001, Reynolds and D'antonio, 1996). However the review of Ostertag (2001), which compile large number of study on effect of fertilization on fine roots, found a general pattern that root density increase after fertilizer application. Additionally King et al. (2002) also concluded from their experiment in loblolly pine roots that the fine root production increased with fertilizer application. Root density is measured either by root length per unit volume (root length density) of root mass per unit volume (root dry matter). Since the nutrients absorption process occurs through the unlignified part of the roots, the root length density in a volume of soil is a better indicator of root ability to absorb nutrients and water compare to root dry matter. The measurement of root dry matter is useful for an indicator of plant investment to the root system and also for root contribution to organic matter in the soil (Oliveira et al., 2000). Another important parameter to measure is specific root length (SRL), which is the length of root per unit weight (cm/g) or the ratio of root length to root mass. Higher SRL implies larger amount of root length presented per gram of root dry matter. This parameter is relatively important indicator for root ability to explore soil (Atkinson, 2000, Eissenstat, 1991). Some studies suggest that a plant with higher value of SRL is able to increase the total root length more easily and elongate faster, compare with plant that has low value of SRL, and therefore has higher rate of nutrient and water uptake (Cornelissen et al., 2003, Fageria, 2013) . Studying root system has been done in the laboratory and in the field. Atkinson and Dawson (2000) reviewed all methods that can be used in the field and categorized them into main groups as follows:
1. Root system removal methods Full excavation, partial excavation (soil monolith, needle boards, soil cores, ingrowth bags) and profile walls are some methods that have been used to study root systems and can be classified into this group. The roots have to be removed from the soil or observed in the location. The assessment of roots using this group of method provide information on root distribution and the mass of standing plant, however the information is limited to a particular time. The excavation method is not suitable to estimate root length because of large loss of fine roots during the excavation (Atkinson and Dawson, 2000). The excavation method is more suitable to assess the development of the whole root system in response to soil type or soil
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feature such as drainage and water availability. Profile wall method is also known as trench method, where the pit is dug at some distance from the tree to expose vertical soil profile. The soil wall method is labor intensive, time consuming and very destructive to the soil however, unlike the needle board and soil coring method, this trench method can be done in stony soil. Some parameters that can be assessed with soil wall methods are root diameter, number, length and distribution. Soil monolith, soil cores, needle boards and ingrowth bag methods can be categorized into the partial excavation. The disadvantage of partial excavation is usually the samples have high spatial variation due to soil conditions, however the partial excavation method, with soil coring or ingrowth bag methods for example, could give the estimation of temporal change in root length or weigh. Soil coring and ingrowth bag methods are also less destructive to the plant and the soil.
2. Observation methods; such as using rhizotron, mini rhizotron, observation window or large walk-in facility. These methods allow researchers to study the development of roots over time and in a non-destructive way, however correlation with root length density is poor (Bengough et al., 2000). The data from observation method can be converted into a root length per unit soil surface (cm/cm2) or root length per unit soil volume (cm/cm3) as long as the observed roots are a valid representative for the whole observed soil volume in respect to root distribution, density, turnover and new growth.
3. Indirect methods through observation of root activities, for example the uptake of soil water or radioisotopes, the release of carbon, or the removal of nutrients from the soil. The indirect methods rely heavily on several assumptions and estimations, for example water depletion can be an indicator of the depth of effective roots but cannot indicate rooting activity and distribution. Root uptakes on a radioisotope (32P) can give an estimation of root depths and horizontal positions. However this method is less effective for perennial crops compare with annual crops.
Choosing the right method to study root depends on the aim of the study, the information that is needed, and the type of root system that will be studied. The choice of method is usually limited by type of root system, field conditions such as crop and soil types, and the availability of equipment and facilities. Hertel and Leuschner (2002) compared different methods, namely soil coring, ingrowth, and root chamber, for studying fine root production. The study found the results of fine root measurement vary widely and concluded that the most reliable method is using soil coring with large number of replicates. In determining the root length, various techniques are available both manual and automated. The automated techniques are mostly using image analysis software and require more time for cleaning the roots because the system cannot distinguish roots from other unwanted organic debris (Oliveira et al., 2000). On the other hand, manual technique can be done by (1) direct measurement, where the length of roots are measure one by one, (2) line intersection method, where the length is estimated using intercept counting technique (Newman, 1966, Tennant, 1975), and (3) visual estimation method where roots are rated subjectively based on standard samples (Walters and Wehner, 1994). The Tennant (1975) method is one of the
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most used techniques because it is practical, reliable, and can be used for different sizes of roots (Oliveira et al., 2000). Several modifications of the Tennant method have been studied, including using subsampling (Bohm, 1979). Root study is a tedious work that is very laborious and time consuming. The time and labor needed increase with the precision of the results. Therefore when deciding what method to use in a root study, one also needs to consider how much time and labor is available for the study.
1.3 Problem statements Studying oil palm root distribution, especially the distribution of fine roots, and its response to different management practices could give a better BMP approach on the plantation particularly on the efficiency of fertilizer management. Some studies have been conducted on the oil palm root response to local nutrient availability (Fairhurst, 1996, Kheong et al., 2010), but these were not comparing between differently managed fields. As demonstrated in previous studies on other plants, different managements, especially fertilization management, in a long-term result in different availability of nutrients that could affect plant root density as well as plant root response to sudden change of nutrient availability (Leuschner et al., 2004, Hodge, 2004, Ostertag, 2001, Reynolds and D'antonio, 1996). The result of studies about root response to local nutrient availability varies. Leuschner et al. (2004) conclude that influence of variation in soil fertility only have weak effect on fine root system. However, Ostertag (2001) and King et al. (2002) found that fine root density tended to increase after fertilizer application, while Fageria (2013) argues that addition of chemical fertilizer in soils with nutrient deficiencies may decreases root length but increase root weight in a quadratic manner. Most of those studies were assessing trees in the forest area with natural gradient of fertility. We did not know whether the same response can be observed in the palm oil plantation where the tree was managed individually, especially for in fertilization management. Our study will observe root distribution of oil palm in response to short term change of nutrient availability as well as the differences caused by long-term management.
1.4 Research Questions and Hypotheses The main research question for the study is “Does improved management (especially fertilization) result in a change in oil palm root density?” The sub questions are as follows:
1. Does the placement of fertilizers and soil organic matter affect the growth of roots?
2. Is the effect of these interventions on root density different at different soil depths?
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3. Does an intervention of different fertilization practices affect oil palm root growth on the short term (after 4 months)?
Hypotheses:
1. Fine root density (RLD and RDM) will be increased at the frond stack zone after intervention of fertilizer application but the Specific Root Length (SRL) will be decreased
2. Fine root density (RLD and RDM) will be higher at the first 15cm soil depth but the SRL will be lower
3. Fine root density (RLD and RDM) in BMP plot will be higher than in REF plot but the SRL will be lower
4. Fine root density (RLD and RDM) will be higher in the area with higher nutrients availability but the SRL will be lower.
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2 Material and Methods
2.1 Study Site
The study site is located in Ramin village, Kumpeh District, Jambi Province, Indonesia (-1.49, 103.8) with an elevation of 6-10m above sea level1, an average temperature of 26.80C, an average humidity of 83%, and a total precipitation of 2093.6 mm/year with a rainy season from December to March and a dry season from June to August (BPS-Statistics of Jambi Province, 2013). The state own company established a plantation in 2002 as part of government project through a nucleus-plasma scheme. In this scheme, the company that develop new plantation has to establish plots for smallholders (plasma) around their main plantation (nucleus). Generally the plasma farmers owned 2ha of oil palm plantation that were transferred to them after 3-4 years (Vermeulen and Goad, 2006). Therefore the plantation has the same land preparation, the same seedling, and the same age of trees. Each farmer in the study area has on average 2-4 ha of oil palm plantation which he manages individually based on his own knowledge and resources. The oil palm trees were in their productive age at the time of our research (12 years), with estimated yields ranging from 1.47 to 3.67 ton/ha/month in the low and peak months, respectively2. Six farmers in the area were selected to join the better management practice project that was conducted by Wageningen University and Research Centre and SNV. Each farmer has 2 ha oil palm fields for the project. The participants were selected non-randomly through a local leader, based on the suitability of their field (full stand of trees, higher ground, mineral soil) and the owner’s willingness to participate. For the purpose of our study, 2 fields from those were selected for root growth study. The selection were based on their contrast on productivity and past management practices, and also because they were located next to each other. Further explanations on each field will be presented in the next section.
2.2 Experimental Design and sampling locations In our study, we used two fields owned by two different farmers. The first field has a good management history and has better appearance of the oil palm trees, while the 2nd field has the opposite. The first field has a production record for 2013 with an average production 1.6 ton/ha/month of fresh fruit bunches2 (ffb). The 2nd field did not have the record and the farmer estimated2 average yield of 0.8 ton/ha/month ffb . Other differences in management between two fields are presented in table 1. Each field was divided into two plots (Figure 3): in the first plot the farmer is still continuing his own management practices (reference/REF plots) and in the other plot, better management practices were implemented (BMP plots) where the
1 http://www.mapdevelopers.com/elevation_calculator.php accessed 9 January 2015 2 Woittiez, 2014 (personal communication)
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amount, type and the way of application of fertilizer were done differently from farmer’s common practices. Table 1. Different management practices between two fields2 Management Field 1 (Good) Field 2 (Poor) Weeding frequency (average/year) 3 2 Herbicide applied Clean-up and Gramoxone - Herbicide application Blanket spraying - Pruning frequency (average / year) 2 2 Harvest frequency (days interval) 15 15 Fertilizers applied NPK, Urea, ZA, SP36, KCL,
Dolomite, Borax, Organic fertilizers
Urea,SP-36, Bacterial solution.
Fertilizers placement Circle zone Circle zone
Figure 3. Experimental set up and sampling locations (FS= frond stack)
Farmers usually spread the fertilizer in the surrounding of the tree based to 2m distance that were cleared from the weeds (also known as weeded circle), while placement of fertilizers in the BMP plots were all around the field. Some new practices in BMP plots that are not always being done in REF plots are as follows:
1. Farmers have weeded circle around each tree, harvesting path and only remove noxious undergrowth.
2. The placement of fertilizers is not in the circle but outside the circle area within the field
3. Different amount and types of fertilizers are applied (rock phosphate, potassium chloride, urea and borax)
4. Harvesting is done every 10 days. The following fertilizers were applied in BMP plots during April and May 2014:
5 kg/tree reactive rock phosphate was broadcasted throughout the plantation (25% P2O5)
0.75 kg/tree urea was spread around the weeded circle (46% N) 1 kg/tree KCl was spread over the frond stack (60% K2O) 200 g borax/tree was spread in the weeded circle (11% B)
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Within each plot, samples were collected from 6 trees. The root samples were taken from 2 zones in each tree. The first zone is the circle zone, which is the area surrounding the tree base that are cleared from weeds. The other is the frond stack zone, which is the area where farmer places their pruned leaves. The roots were sampled to 30cm depth and divided into the first 15cm and the next 15cm (Figure 3). There are no physical or chemical barriers that could affect or alter root growth, and all plots are located next to each other on the same type of soil. Thus the differences of root growth between plots and sampling locations are expected to come from the management that influence soil properties and nutrients availability
2.3 Root sampling To observe root growth in differently managed fields through an assessment of root length density and root dry mass, we selected the core sampling method because it will not cause massive disturbance to the observed trees and allows to compare different locations and management treatments. Thus for our study, root samples will be extracted with soil core from the top 30 cm of the soil and will be analyzed separately at 0-15 and 15-30 depth. As explained in the previous section, the samples were taken from six trees per plot. For each tree, roots were sampled from two zones, which are in circle zone 0.5m from the trunk, and under the frond stack at 3 m from the trunk (Figure 4).
The method of root sample extraction followed Fairhurst (1996) and Kheong et al. (2010), using a root auger with a core diameter of 8 cm and a length of 15 cm with a serrated edge at the bottom (Figure 5). The sample collection and laboratory analyses were done from August to September 2014.
x
x = sampling location, 0.5 m and 3 m from the tree
= frond stack = harvesting path
= oil palm tree x
Figure 4. Sampling locations in each selected tree
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Figure 5. Single root auger (adapted from www.eijkelkamp.com)
When taking the sample, any weeds and other organic materials were removed from the soil surface. For the first sample (0-15 cm) the auger was placed onto the soil and twisted and pushed downwards until the cylinder was completely filled with soil (Figure 5). The hole were measured (15 cm depth) to get the precise volume. The remaining soil at the bottom of the hole that were not completely taken by the core were collected by hand. The sample was removed from the cylinder by pushing the plunger down and stored in a plastic bag to be transported to the laboratory. The second sample (15-30 cm) was taken directly after the first from the same sampling hole and according to the same protocol. The depth of the hole was determined using a measuring tape. All samples were transported to the laboratory and pre-soaked for a night on the same day for further handling as explained in section 2.5.
2.4 Ingrowth method Ingrowth core method was done to see the net root growth response to fertilizer and estimate the new fine root productions. The ingrowth methods followed the method describe in Steingrobe et al. (2000) as follows:
1. With a soil core (diameter 5cm) a hole of 42.4 cm were dug at 45 degree angle
2. Soil from the core was carefully collected and any visible roots and other organic matters were removed manually.
3. The Ingrowth bag (diameter 5cm, length 50cm, mesh size 3mm) made from a plastic mesh was pulled onto a PVC tube (5cm) and inserted into the hole.
4. For the control bags, the same soil was placed back into the mesh bag after removal of roots and organic debris. To insert the soil, the PVC tube was pulled out from the mesh bag for a few cm and soil was inserted and compressed by a wooden stick to get the relatively same soil density with surrounding soil. The remaining soil was inserted little by little with the same process until it fills the mesh bag completely.
5. For the treatment bags, 6 gram NPK fertilizer (16-16-16) was diluted in the water before mixed into the soil. The fertilizer was sprayed and mixed into the soil by hand. The soil was inserted into the ingrowth bag with the same procedures as in control bag.
6. The ingrowth bags were placed next to 12 different trees from the REF plot in field 2 that had poor management, in order to see roots response to nutrient availability.
7. Mesh bags with fertilizer treatment were placed next to 6 trees, while the other 6 trees had control mesh bags.
119 cm
handle
cylinder Serrated edge
plunger
15 cm
8 cm
15
8. Each mesh bag was positioned at 2 m distance from the trunk to the frond stack direction (Figure 4).
9. The mesh bags were pulled out after 4 weeks and placed into plastic bag for transportation.
10. The roots were brought into laboratory and pre-soaked for a night in the same day and followed the same method as for the auger sample as explain in section 2.5.
2.5 Root Measurement Samples from the field were stored in plastic bags and pre-soaked overnight (15-18 hours) in 1 liter water with 1g sodium hexametaphosphate (Noordwijk, 1993). Root collection was done manually by washing roots from soil. The pre-soaked soil were washed through 3mm sieve on top of the bucket and gently stroke while spraying water to make the soil dissolved. The remaining water in the bucket that contains some small roots that escaped 3mm sieve then filtered through 2mm sieve (Figure 6a). The procedures were repeated until all roots are clean from soil. The visible dead roots were separated from the live roots. The live clean roots were placed in a plastic filled with water and stored in the refrigerator. Root samples that could not be measured on the same day were stored for a maximum of 5 days. The root length was measured using the intersection method (Newman, 1966, Tennant, 1975). Roots were divided into 3 classes based on diameter into (1) primary; > 6 mm), (2) secondary; 2-5 mm) and (3) fine roots (tertiary; 0.5-2 mm and quaternary; <0.5 mm) using the Fairhurst (1996) graph that follows Tinker’s (1976) classification (graph in Appendix I). The counting was done based on each root class. The roots were spread on a clear tray with a printed 1 cm grid at the bottom (Figure 6b). The number of root intersections to the grid was counted. Total root length was calculated by multiplying the total number of grid intersections with a conversion factor of 0.7857 (Tennant, 1975). Root dry weight was recorded after the root samples of each root class were oven-dried at 700C for 48 hours (Oliveira et al., 2000) Root parameters were calculated as follow;
1. Root length density (cm/cm3) was calculated by dividing total root length over the volume of the soil core (750 cm3). The results were then converted to mm/cm3 and used for further analysis.
2. Root dry matter was calculated by dividing total root biomass (g) after drying over the volume of soil sample (750 cm3). The results were then converted to mg/cm3 and used for further analysis.
3. Specific root length (cm/g) was calculated by dividing the root length density over root dry matter.
16
Figure 6. Washed roots (a) and the intersection method using 1cm x 1cm paper grid to calculate root
length (b)
2.6 Statistical Analysis
A paired t-test (IBM SPSS Statistic 22) was used to calculate differences between soil zones and differences between soil depths, while an independent t-test was used to calculate differences between plots and differences between fields. The test was carried out for all root parameters; Root Length Density (RLD), Root Dry Matter (RDM), and Specific Root Length (SRL) for each root class (primary, secondary and fine roots) as explained below;
1. Different Soil Zones Total roots in 0-30 cm soil depth were used to test the difference between roots in the circle and the frond stack zones. The samples were pooled from different plots and fields. The grouping and paired variables are presented in table 2. Table 2. Statistical analysis arrangement to compare roots parameters at
different soil zones Groups Paired variables N Parameters
Primary roots Circle Frond stack
24 24
RLD ; RDM ; SRL
Secondary roots Circle Frond stack
24 24
RLD ; RDM ; SRL
Fine roots Circle Frond stack
24 24
RLD ; RDM ; SRL
2. Different Soil Depths
The test compared roots parameters between 0-15cm soil depth and 15-30cm depth at different soil zones as presented in table 3. There was no differentiation between plots and fields. Table 3. Statistical analysis arrangement to compare roots parameters at
different soil depths Groups Paired variables N Parameters
Primary roots 1. Circle: 0-15cm Circle :15-30 cm
24 24
RLD ; RDM ; SRL
a) b)
17
2. Frond stack 0-15cm Frond stack 15-30cm
24 24
RLD ; RDM ; SRL
Secondary roots 1. Circle: 0-15cm Circle : 15-30 cm
2. Frond stack 0-15cm Frond stack 15-30cm
24 24 24 24
RLD ; RDM ; SRL RLD ; RDM ; SRL
Fine roots 1. Circle: 0-15cm Circle: 15-30 cm
2. Frond stack 0-15cm Frond stack 15-30cm
24 24 24 24
RLD ; RDM ; SRL RLD ; RDM ; SRL
3. Different Plots
The t-test was used to calculate differences between BMP plot and REF plot. Total roots from 0-30cm soil depth were used for this calculation. The samples were pooled from both the good and poor performance fields and separated based on root classes and soil zones. Table 4. Statistical analysis arrangement to compare roots parameters at
different plots Groups Sub-groups Variables N Parameters
Primary roots Circle
BMP REF
12 12
RLD ; RDM ; SRL
Frond stack BMP REF
12 12
RLD ; RDM ; SRL
Secondary roots Circle
BMP REF
12 12
RLD ; RDM ; SRL
Frond stack BMP REF
12 12
RLD ; RDM ; SRL
Fine roots Circle
BMP REF
12 12
RLD ; RDM ; SRL
Frond stack BMP REF
12 12
RLD ; RDM ; SRL
4. Different Fields
The t-test was used to calculate differences between previously poor and good management fields. Total roots form 0-30 cm depth was used for this analysis. There was no differentiation of BMP and REF plots but grouping was performed based on root classes and soil zones. Table 5. Statistical analysis arrangement to compare roots parameters at
different fields Groups Sub-groups Variables N Parameters
Primary roots Circle
Good field Poor field
12 12
RLD ; RDM ; SRL
Frond stack Good field Poor field
12 12
RLD ; RDM ; SRL
18
Secondary roots Circle
Good field Poor field
12 12
RLD ; RDM ; SRL
Frond stack Good field Poor field
12 12
RLD ; RDM ; SRL
Fine roots Circle
Good field Poor field
12 12
RLD ; RDM ; SRL
Frond stack Good field Poor field
12 12
RLD ; RDM ; SRL
5. Ingrowth study
For the ingrowth bag study, the means between treatments and REF were compared using a t-test (N=6).
19
3 Results 3.1 Root Length Density (RLD), Root Dry Matter (RDM) and Specific Root Length
(SRL) at different soil zones In general, the RLD in circle zone is higher than in the frond stack zone in all root classes (Figure 7), however the difference is not statistically significant for fine roots (Figure 7c). Total RLD for all classes of roots in the circle zone is 21.17 mm/cm3 on average while in frond stack is 16.17mm/cm3. The same patterns are also found in the RDM values (Figure 8) where the mean of RDM in the circle zone is significantly higher than in the frond stack zone for all root classes (p<0.05). While the value of SRL for all classes of roots seems higher in the frond stack zone compare to the circle zone area (Figure 9), however only the differences in secondary and fine roots were statistically significant (p < 0.05). When comparing the composition of the roots based on its class to the total roots in the area, we can observe that fine root density contributes to over 80% of total root density per cm3 in the circle zone and over 90% in the frond stack zone (Table 6). For the root biomass (RDM), we can see that the primary roots contribute more than 74% to total dry mass per cm3 in the circle zone, but only 30% in the frond stack zone, where the fine roots contribute more than 40% (Table 6).
Figure 7. Root length density at different soil zones for different root classes of 12 years old oil palm
tree (bars represent standard error mean, * means significant difference at p<0.05)
0.0
0.5
1.0
1.5
2.0
2.5
Circle Frondstack
Ro
ot
Le
ng
th D
en
sity
(m
m/
cm3
)
a) Primary Roots
0.0
0.5
1.0
1.5
2.0
2.5
Circle Frondstack
b) Secondary Roots
0.0
5.0
10.0
15.0
20.0
25.0
Circle Frondstack
c) Fine Roots
*
*
20
Figure 8. Root dry matter at different soil zones for different root classes (bars represent standard
error mean, * means significant difference at p<0.05)
Figure 9. Specific root length of different root classes in different soil zone. (bars represent standard
error mean, * means significant difference at p<0.05)
Table 6. The contribution of each root class to total root length density (RLD) and total Root Dry matter
(RDM) per cm3 in 12 years old oil palm tree at circle zone (n=24) and frond stack (n =24 ) zone.
Root Parameter/ Class
RLD (%) RDM (%)
Circle FS Circle FS
Primary 6.76 1.24 74.84 32.11
Secondary 9.45 8.71 11.64 25.69
Fine roots 83.79 90.05 13.55 42.20
total 100 100 100 100
FS= frond stack
0
2
4
6
8
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12
14
Circle Frondstack
Ro
ot
Dry
Ma
tte
r (m
g/
cm3
)
a) Primary Roots
0.0
0.5
1.0
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2.0
2.5
Circle Frondstack
b) Secondary Roots
0.0
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Circle Frondstack
c) Fine Roots
0
5
10
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Circle Frondstack
Sp
eci
fic
Ro
ot
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ng
th (
cm/
g)
a) Primary Roots
0
50
100
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250
Circle Frondstack
b) Secondary Roots
0
200
400
600
800
1000
1200
Circle Frondstack
c) Fine Roots
*
*
*
*
*
21
3.2 Root distribution at different soil depths Figure 10 presents the RLD of oil palm roots at different soil depths in the circle zone and frond stack zone. The RLD of fine roots (Figure 10c) is significantly higher (p<0.05) in 0-15 cm depth compared with 15-30 cm depth both in the circle and the frond stack zone (the average values are 24.21mm/cm3 and 11.26mm/cm3, respectively). The same pattern is observed in secondary and primary roots in the frond stack zone but not in the circle zone (Figure 10a and Figure 10b). The same results are found for RDM (Figure 11) where significantly higher amounts of root dry matter (p>0.05) were observed in the first 15 cm compare with 15-30 cm depth in front stack zone for all root classes. However in the circle zone, the differences in dry matter of primary and secondary roots do not significantly differ between soil depths (Figure 11 and Figure 11b). In contrast, there is no clear pattern of SRL values between different soil depth. The only statistically significant difference is found in secondary roots in circle zone, where the SRL of roots in the first 15cm depth is higher than 15-30 cm soil depth (Figure 12b), while other mean differences are not statistically significant (Figure 12).
Figure 10. Root length density (a) primary (b) secondary and (c) fine roots of 12 years old oil palm tree
at different soil depths. * means statistically significant (p<0.05). Bars represent standard errors of the means
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Circle Frondstack
Ro
ot
Le
ng
th D
en
sity
(m
m/
cm3)
a) Primary Roots
0 - 15 cm15 - 30 cm
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Circle Frondstack
b) Secondary Roots
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Circle Frondstack
c) Fine Roots
*
*
*
*
22
Figure 11. Root Dry Matter (a) primary (b) secondary and (c) fine root of 12 years old oil palm tree at
different soil depths. * means statistically significant (p<0.05). Bars represent standard errors of the means
Figure 12. Specific Root length (SRL) (a) primary (b) secondary and (c) fine root of 12 years old oil palm
tree at different soil depths. * means statistically significant (p<0.05). Bars represent standard errors of the means.
3.3 RLD, RDM and SRL in different plots
The comparison between BMP and REF plots was made for each root class in the circle zone and in the frond stack zone, for RLD, RDM, and SRL mean values (Figure 13, Figure 14, Figure 15 respectively). The results were similar for RLD and RDM. Only the RLD and RDM of secondary roots in the frond stack zone were significantly higher in BMP plots compared with REF plots (p<0.05) (Figure 13b and Figure 14b). The differences between BMP and REF plots were not statistically significant for primary, secondary and fine roots in the circle zone area (both for RLD and RDM), as well as for primary and fine roots in the frond stack zone (data are presented in Annex II, Table 11 and Table 12). Meanwhile the SRL values in REF plots are higher than in BMP plots for all root classes in the frond stack zone (p< 0.05) but not in the circle zone (Figure 15).
0
2
4
6
8
10
12
14
16
Circle Frondstack
Ro
ot
Dry
Ma
tte
r (m
g/
cm3)
a) Primary Roots
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Circle Frondstack
b) Secondary Roots
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Circle Frondstack
c) Fine Roots
0 - 15 cm15 - 30 cm
0
5
10
15
20
25
Circle Frondstack
Sp
eci
fic
Ro
ot
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ng
th (
cm/
g)
a) Primary Roots
0 - 15 cm15 - 30 cm
0
50
100
150
200
250
300
350
400
450
Circle Frondstack
b) Secondary Roots
0
200
400
600
800
1000
1200
1400
Circle Frondstack
c) Fine Roots
* * *
*
*
23
Figure 13. Comparison of RLD in BMP and REF plots in each soil zone. * means statistically significant
(p<0.05). Bars represent standard errors of the means
Figure 14. Comparison of RDM in BMP and REF plots at different soil zones. * means statistically
significant (p<0.05). Bars represent standard errors of the means
Figure 15. Specific root length in BMP and REF plots at different soil zones. * means statistically
significant (p<0.05). Bars represent standard errors of the means
0.0
0.5
1.0
1.5
2.0
2.5
Circle Frondstack
Ro
ot
len
gth
De
nsi
ty (
mm
/cm
3)
a) Primary Roots
0.0
0.5
1.0
1.5
2.0
2.5
Circle Frondstack
b) Secondary Roots
0.0
5.0
10.0
15.0
20.0
25.0
Circle Frondstack
c) Fine Roots BMPREF
0.0
2.0
4.0
6.0
8.0
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12.0
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16.0
Circle Frondstack
Ro
ot
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Ma
tte
r (m
g/
cm3
)
a) Primary Roots
0.0
0.5
1.0
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2.0
2.5
3.0
Circle Frondstack
b) Secondary Roots
0.0
0.5
1.0
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3.0
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c) Fine Roots
BMPREF
0
5
10
15
20
25
30
Circle Frondstack
Sp
eci
fic
Ro
ot
len
gth
(g
/cm
)
a) Primary Roots
BMPREF
0
50
100
150
200
250
Circle Frondstack
b) Secondary Roots
0
200
400
600
800
1000
1200
1400
Circle Frondstack
c) Fine Roots
*
*
* *
*
24
3.4 RLD, RDM and SRL in different fields
Another comparison was done between field 1 and field 2 which are owned by different farmers and have been subjected to different management practices in the past. This comparison was used to observe any difference in root growth between fields that previously had good management (field 1) and poor management (field 2). The statistical analysis using t-test shows that the differences between fields were not statically significant for RLD, RDM or SRL for any root class (Figure 16, Figure 17, and Figure 18, data presented in Annex II Table 13 and Table 14)
Figure 16. Comparison of RLD between good and poor managed fields at different soil zones. Bars
represent standard error of mean. * means statistically significant (p<0.05)
Figure 17. Comparison of RDM between Good and Poor managed fields at different soil zones. Bars
represent standard error of mean. * means statistically significant (p<0.05)
0.0
0.5
1.0
1.5
2.0
2.5
Circle Frondstack
Ro
ot
len
gth
De
nsi
ty (
mm
/cm
3)
a) Primary Roots
0.0
0.5
1.0
1.5
2.0
2.5
Circle Frondstack
b) Secondary Roots
0.0
5.0
10.0
15.0
20.0
25.0
Circle Frondstack
c) Fine Roots
GoodPoor
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
Circle Frondstack
Ro
ot
Dry
Ma
tte
r (m
g/
cm3
)
a) Primary Roots
0.0
0.5
1.0
1.5
2.0
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3.0
Circle Frondstack
b) Secondary Roots
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Circle Frondstack
c) Fine Roots
GoodPoor
25
Figure 18. Specific root length density in differently managed fields per root class. Bars represent
standard error of mean. * means statistically significant (p<0.05)
3.5 Ingrowth bag
The ingrowth mesh bag had a volume of 834.39 cm3, therefore RLD was calculated by dividing calculated root length by the volume of the mesh bags. The same procedure was followed for the RDM. All roots found in the mesh bag were fine roots, so there was no categorization of root classes in the counting and weighing procedures. The results did not confirm the hypothesis that the RLD would be higher in fertilized bags, there were no differences between the control and the fertilizer treatments for both RLD and RDM (Figure 19).
Figure 19. Root length density (a) and root dry matter (b) in fertilizer and control ingrowth bags (bars
represent standard errors of the means, n=6), difference to control is not significant at p=0.05).
0
5
10
15
20
25
30
Circle Frondstack
Sp
eci
fic
Ro
ot
len
gth
(cm
/g
) a) Primary Roots
GoodPoor
0
50
100
150
200
250
Circle Frondstack
b) Secondary Roots
0
200
400
600
800
1000
1200
1400
Circle Frondstack
c) Fine Roots
0
1
2
3
4
5
6
Control Fertilizer
Ro
ot
len
gth
de
nsi
ty (
mm
/cm
3)
Treatment
0
5
10
15
20
25
30
35
40
Control Fertilizer
Ro
ot
dry
ma
tte
r (m
g/
cm3)
Treatment
a)RLD b) RDM
26
27
4 Discussion 4.1 RLD, RDM, and SRL in different zones
RLD and RDM in the circle zone was higher than in the frond stack zone when all data were pooled per zone (Figure 7 and Figure 8). It was expected that the RLD and RDM would decrease from the tree based outward. Our results confirm the results of Fairhurst (1996) which showed that total root length (RLD) and root mass (RDM) in the circle zone was higher than in the frond stack zone. However he also observed that root length of tertiary roots was higher in the frond stack zone compared with the circle zone (Fairhurst, 1996), but not for quaternary roots. In our study, tertiary and quaternary roots categories were summed up into one category which is fine roots and we did not find significant different between circle and frond stack zones. We were expecting to observe a higher fine root length density in the frond stack zone than in circle zone, especially because fertilizer was also applied in frond stack zone in BMP plots. For both BMP and REF plots, the frond stack zones have the accumulation of organic residues from the placement of pruned leaves that was expected to increase root proliferation. However, we did not observe more fine roots in frond stack zone, probably because farmers previously applied fertilizers in the circle zone, thus more fine roots were found in circle zone. In our study the fine root density under the frond stack was the same as in the circle zone. It should be noticed that the root samples in circle zone and frond stack zone were taken at 0.5cm and 3m from tree based respectively. Therefore it was expected to find higher density roots closer to the trunk, as found in the primary and secondary root length density. The RLD of primary and secondary roots were significantly less in frond stack than in the circle (Figure 7) but fine root length density was the same between circle and frond stack zones. It suggests more fine roots in frond stack zone as supported by the composition of root classes in the 30 cm top layer of soil. The RLD in the frond stack zone consists of 90% of fine roots, of which one of the functions is to absorb nutrients. In comparison, in the circle zone the fine roots contribute to around 84% of root density (Table 6). Frond stack zone can be argued as the area with more organic matter since it was supplied through the placement of pruned leaves. Placement of pruned leaves also provide more moisture on the soil under them compare to the bare soil in the circle zone. Since the pruned leaves were always present in the frond stack zone, we were expecting to see more fine roots in there, however the result show no significant difference between fine roots in the frond stack and circle zone. Similar results were also found by Kheong et al. (2010). Their study was comparing oil palm root biomass in the area with and without application of oil palm empty fruit bunches (EFB) at 1m distances from the tree trunk. Their study compared the root biomass after 3 months and 6 months application of EFB with the root biomass of the same tree in the area without EFB application. They only found higher root biomass at 30-45cm depths after 3 months application in the area where the EFB were applied, however after 6 months application they did not find any differences at any soil depth. Meanwhile root biomass in the first 30 cm of soil depth did not show any difference compared with the roots biomass without application of EFB. The significant result after 3 months application of EFB was only observed for the
28
total root biomass but not significant once they separated roots based on root classes. In our study, the effect of more organic matter in the frond stack probably can be seen if we compare the roots to other area at the same distance from the tree, instead of comparing it with the roots in the circle zone that was much closer to the trunk. The results of RDM were consistent with the RLD except for fine root. The RDM of fine roots in frond stack was also significantly lower than in circle zone (Figure 8) and contrastingly, the SRL of fine roots was significantly higher in front stack (Figure 9). In previous experiments, Fairhurst (1996) did not differentiate the root classes in assessing the SRL and he found an SRL of around 391 cm/g in the circle and of around 458 cm/g in the frond stack zone. When we sum the SRL values from all root classes, we found an average SRL of 352.32 cm/g in the circle and 431.37 in the frond stack zone which are in line with the values of Fairhurst’s study. The SRLs we observed highly varied between root classes and increased with root order as also observed in the study of Pregitzer et al. (1997) on different species of trees. We found an SRL of 12 -23 cm/g for primary, 160-204 cm/g for secondary and 935 – 1251 cm/g for fine roots in the frond stack area. As SRL is one of important indicators for root ability to explore the soil, it can be suggested that the fine roots in the frond stack zone have a higher potential to growth in high rate than fine roots in the circle zone. It leads to the ability of root to capture available nutrients. This is supported by Eissenstat (1992) study on citrus roots that found roots with high SRL had the highest rate of root proliferation and highest rate of water extraction.
4.2 RLD, RDM, and SRL at different soil depth In our study, we observed that total RLD decreases with increasing soil depth (Figure 10), in line with the observations of Fairhurst (1996). However, Fairhurst (1996) found that the primary root length density increased from 0-10 cm to 30 cm soil depth both in the circle and in the frond stack soil zone, while in our study we did not see a difference in the circle zone. Fairhurst also observed that secondary root length density was similar at all depths and soil zones, while in our study (Figure 9b and 10b) we found that secondary RLD and RDM decrease significantly with depth in the frond stack zone but not in the circle zone. Other sources implied that the root length density decrease with increase of soil depth (Corley and Tinker, 2003a) mainly because the abundance of resources availability in the surface soil, that is corresponding to the role of fine roots. While the main roles of primary roots that growth both vertical downward (RI VD) and horizontal (RI H) along with secondary vertical downward (RII VD) (Figure 2) are for anchorage and exploring the volume of available soil (Jourdan and Rey, 1997). As can be seen from Figure 2, primary roots growth both downward and horizontal from the base of the tree. In Fairhurst study, the exploration of soil by primary and secondary roots to horizontal area probably in lower depth, therefore he did not find any differences between 0-15 cm and 15-30 cm. While in our study, probably the primary and secondary roots explore horizontally more in the surface. This results in more primary and secondary roots found in the first 15cm depth especially in the frond stack zone because the number of secondary roots per cm length of horizontal
29
primary roots were less at the base of the tree and increasing at around 2-3 m from the tree before lessening further out (Purvis, 1956). Our results agree with Fairhurst (1996) when considering the fine root class, where the RLD and RDM were significantly higher at the top layer soil in both zones. This results shows that the difference of soil depths were more prominent to variation of root density at the frond stack zone. The first top 15cm soil layer in front stack has four times more RLD than the next 15-30 cm depth (data presented in Appendix II). Since fine roots density is associated with nutrients absorption ability, it can be suggested that there is more nutrients available in the top part of soil both at the frond stack and circle zone areas. The difference between soil depths at the frond stack zone can be linked into the availability of organic matter from the frond pile. While for the BMP plots, it also includes the change of chemical fertilizer availability that were applied as well in the frond stack area.
4.3 RLD, RDM and SRL under different management practices After 4 months intervention in the BMP plots, we were expecting the RLD of fine roots in BMP plots will be higher in frond stack area compare with REF plots as result of more nutrient available as observed in previous studies (King, 2003 Ostertag, 2001). However Fageria (2013) argues that addition of chemical fertilizer may decrease root length but increase root weight in a quadratic manner especially in soils with nutrient deficiencies. We cannot confirm this phenomenon from our study as both RLD and RDM were significantly higher in BMP than in reference plots under frond stack for secondary roots and no significant difference was found for the other root types in any zone (Figure 13 and Figure 14, data presented in Appendix II Table 11 and Table 12). Regarding long term effects of nutrient management, we found no significant differences in any root parameters between previously good managed field and poor managed field (Figure 16 and Figure 17, data presented in Appendix II Table 13 and Table 14). The RLD of fine roots was expected to be abundant in previously poorly managed field compare with good managed field because of the scavenging activities of roots in the soil that lack nutrients. Even though we could see weak pattern in figure 14, the differences were not statistically significant at p<0.05 (p=0.06). We found that SRL values were significantly higher in the REF plots compared with in the BMP plots. A high SRL indicates that the roots have invested less carbon to produce the same root length which suggests its ability to proliferate more easily and shows a high capacity for water and nutrient intake compare with roots that have a low SRL value (Fageria, 2013, Eissenstat et al., 2000, Eissenstat, 1991). Like other root parameters, SRL is influenced by environmental factors such as nutrient availability, soil depth and physical conditions, as well as by crop variety, age, and genotype (Oliveira et al., 2000, Fageria, 2013). SRL is suggested to be an indicator on how plants respond to environmental changes including responses to resource availability in the soil and competitive ability with other roots (Atkinson and Dawson, 2000). Fine roots that do not have branches tend to have higher SRLs and shorter life spans compared with secondary and tertiary roots that have branched to a next order of roots (Eissenstat et al., 2000). Eissenstat (1992), who studied
30
roots of citrus, implied that roots with a high SRL had a high rate of root proliferation and a high rate of water extraction. The results from a meta-analysis study by (Ostonen et al., 2007) on natural forest trees showed that SRL decrease significantly under fertilization. Ostonen then suggested the use of SRL as an indicator of nutrient availability in experimental conditions. Therefore finding the higher SRL at the frond stack area in the REF plot in our study suggests that the roots in the REF plot have more scavenging activities for water and other nutrients. However because there are so many other factors that influence SRL, further study is needed in which other sources of variation between plots are controlled especially because in our study, standard deviation values are very high (data in the appendix II) at some groups. Therefore it was not surprising to find statically insignificant differences for SRL It should be noted that the application of fertiliser in the BMP plots were done 4 months before the sampling and each field had different management practices before. Our finding can be used as comparison for further study on long term effect of BMP to oil palm root growth in previously poorly managed field and better managed field. Since root density in infertile soils tends to be higher than in the fertile soils, the response to fertiliser application might be different because of plant resource allocation (Ostertag, 2001), Results from our study don’t show that in the fields, improved management leads to higher root length density compare with poor management. Although we observed differences between the different plots for example in RLD and RDM of secondary roots in frond stack as well as SRL of all root classes in frond stack, it would be better to have true replicates for each plot to confirm that these differences were caused by the management practices of the plot. Otherwise it just shows that root growth in one field is different with the other field, which can be caused by spatial variation from soil compaction to soil moisture at each different tree. Furthermore using soil core method for assessing root distribution can provide accurate information without disturbing the plant, but the information is affected by spatial variation on the soil. Further studies with enough replicates for differently managed plots could help to confirm the effect of management practices on root growth. Further soil analysis at each sample location could also add more information on sources of differences between BMP and REF plots.
4.4 Ingrowth bag We did not find the ingrowth bag result as expected. It was expected that the RLD in treatment bags would be higher than in the control bags as Steingrobe et al. (2000) and Raich et al. (1994) found that high nitrate content resulted in higher RLD in the ingrowth bag experiment. Pregitzer et al. (1993) who studied new fine roots in natural forests using observation method in soil observation chamber (soil biotron) found that roots in the area where nitrogen and water were applied proliferated much faster compared with the area where water alone was applied. After 82 days the average new root length in the area with nitrogen was almost 600% more than in the area without nitrogen. However, there are some other factors that are responsible for root growth besides nutrient availability. In the same study, Steingrobe et al. (2000) found that RLD was lower in a high soil density
31
core, meanwhile Steen and Håkansson (1987) also observed that root mass in compacted soil cores was 20% less than in loose soil cores and Yahya et al. (2010) showed that oil palm’s fine roots are affected by soil compaction. Therefore the unexpected results in this study might be caused by the higher soil density in the fertilized bags. Ingrowth bag method has been used to estimate the root production because of its relatively quick, low cost and less laborious work especially to observe root growth response to manipulated soil conditions, however (Majdi et al., 2005) discussed some major limitation of this method including altered soil structure when the soil was placed in the bag. In this experiment, fertilizers (NPK) was diluted in the water before being mixed into the soil. This resulted in high soil density when the soil was put back into the mesh bag using PVC tube and wooden stick to help in filling the mesh. This is worsened by the type of the soil which is clay soil. Even though the same amount of soil was used to fill the mesh bags both for treatment and control, mesh bags filled with fertilized soil had some gaps at the top part due to the more compaction, while mesh bags filled with control soil had more soil on top part. Steingrobe et al. (2000) noted that having the equivalent amount of soil before adding to the mesh bag just resulted into the average soil density in the bag but doesn’t count for the uniform distribution of soil density inside the cores, as found in this study when the mesh bag were collected, some bags had gaps inside the core. In our study, the removal of root in the filling soil was done by hand and was not done thoroughly for all fine roots because of limited time and assumption that small roots would decay and could easily be distinguished after 4 weeks. However after collecting the mesh bags, it was difficult to distinguish 4 weeks old dead roots from new roots because of their appearances. Sieving the soil to remove fine roots needs time and is an intensive work, The soil is prone to rapid mineralization when it’s done in a high temperature environment that could result in higher mineral N content (Steingrobe et al., 2000). Steingrobe et al. (2000) used soil from the experimental site that was collected beforehand and went through sieving and storing processes in low temperature to reduce mineralization process. Previous studies discourage the use of roots free natural soil to avoid having soil with low cation exchange capacity (CEC) in the mesh bag that would reduce the cation retention capacity that is useful for the study (Smith et al., 2005). Instead, they used calcine clay (Raich et al., 1994) and vermiculite or perlite (Hairiah et al., 1991) to assure high CEC and soil free of N and P.
4.5 Recommendation for further study Our experimental design did not have replicates for both poor and good managed fields. Therefore the comparison of roots between these two fields does not have strong power to show that any difference is due to the different management. To make strong correlation of the difference to the management, more replicates of poor and good managed fields are needed. The same goes for BMP and REF plots. In our study, we only have 2 replicate plots for each. Instead of having many sampling in each plot, it would be better to have more plots as replicates than sub samples in the plot to increase the statistical power of the difference between those plots.
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Further studies to compare root density could compare roots in the frond stack area with roots in an area at the same distance from the tree but without the pile of fronds, instead of comparing only with the roots in the circle zone. However it should be kept in mind not to compare with roots in the path zone since Fairhurst (1996) and Yahya (2010) found that soil compaction negatively affected oil palm root growth. For ingrowth bag study, it is necessary to sieve the filling soil before store it back to the mesh bag to avoid confusion of old dead roots and new root. The application of fertilizer should not be done by dilute it in water since it could change soil density in the mesh bag, grinded fertilizer could be an option.
33
5 Concluding Remarks This study confirmed that oil palm root density decrease with distance from the tree as well as with depth of soil except for the fine roots that were in the similar density between the circle and the frond stack zone at the first 30cm soil depth. It suggest that for the adult oil palm tree, the area outside the circle zone is as important as circle zone for root’s water and nutrients uptake especially with the result of specific root length density of fine roots that is higher at the frond stack compare with at circle zone. It implies fine root’s ability to proliferate is higher in frond stack compare with circle zone. Therefore fertilizer application should not only focus on the circle zone. Different management practices whether in the short time and in the long term do not show significant differences in the oil palm root length density and root dry matter. However we found higher specific root length of fine roots in the REF compare with BMP plots that suggest higher plasticity of fine roots in the reference plots. It could also suggest that fine roots in the BMP plots has higher biomass per cm root length as a response to chemical fertilizer application that increase root weight in a quadratic way especially when the roots were previously in a nutrient-deficit soil (Fageria, 2013). Further soil analysis could be done to confirm that the difference of root density in the field was caused by variation of nutrient available as a result of different management practices. This study can be used as base line study of oil palm root growth at different management practices. The result from ingrowth bag experiment cannot answer the question about roots response to the nutrient availability but could show roots response to different soil density and soil compaction.
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Appendixes
Appendix I. Root Classification to distinguish primary, secondary and fine roots from root samples (Fairhurst, 1996)
Primary roots 10 mm 6 mm
Secondary roots 4 mm 2 mm
Fine roots (tertiary and quaternary roots)
< 1.2 mm
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Appendix II. Data and Statistical Analysis Results
1. RLD, RDM and SRL at different soil zones (correspondent to Figure 6Figure 7, Figure 8 and Figure 9 respectively)
Table 7. Group Statistics for RLD, RDM and SRL at different soil zones
Root Class Paired Mean N Std.
Deviation Std. Error
Mean
Root Length Density (RLD) (mm/cm3)
Primary Circle 1.43 24 0.89 0.18
Frondstack 0.20 24 0.17 0.03
Secondary Circle 2.00 24 1.13 0.23
Frondstack 1.41 24 0.59 0.12
Fine Circle 17.73 24 10.37 2.12
Frondstack 14.57 24 6.31 1.29
Root Dry Matter (RDM) (mg/cm3) Primary Circle 11.21 24 7.06 1.44
Frondstack 1.05 24 1.00 0.20
Secondary Circle 1.74 24 1.23 0.25
Frondstack 0.84 24 0.48 0.10
Fine Circle 2.03 24 1.22 0.25
Frondstack 1.38 24 0.61 0.12
Specific Root Length (SRL) (cm/g) Primary Circle 12.83 24 2.78 0.57
Frondstack 17.98 24 12.78 2.61
Secondary Circle 132.82 24 49.08 10.02
Frondstack 182.46 24 43.49 8.88
Fine Circle 911.31 24 288.16 58.82
Frondstack 1093.67 24 207.95 42.45
Table 8. Paired t-test results at different soil zones
Class Paired Paired differences
95% confident interval of the
difference t df
difference
Sig (2-tailed)
Mean SD SE Lower Upper
Root Length Density Primary Circle - FS 1.23 0.90 0.18 0.85 1.61 6.68 23 0*
Secondary Circle - FS 0.60 1.23 0.25 0.08 1.12 2.37 23 0.027*
Fine Circle - FS 3.17 12.50 2.55 -2.11 8.44 1.24 23 0.227
Root Dry Matter
Primary Circle - FS 10.16 7.16 1.46 7.14 13.19 6.95 23 0*
Secondary Circle - FS 0.90 1.38 0.28 0.32 1.48 3.21 23 0.004*
Fine Circle - FS 0.65 1.39 0.28 0.06 1.23 2.28 23 0.032*
Specific Root Length
Primary Circle - FS -5.14 13.13 2.68 -10.69 0.40 -1.92 23 0.067
Secondary Circle - FS -49.65 67.33 13.74 -78.08 -21.22 -3.61 23 0.001*
Fine Circle - FS -182.36 348.15 71.07 -329.37 -35.35 -2.57 23 0.017*
*) means are statistically significant at p<0.05
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2. RLD, RDM and SRL at different soil depths (correspondent to Figure 10, Figure 11 and Figure 12respectively)
Table 9. Group Statistics of RLD, RDM and SRL at different soil depth
Root Class Paired depth Mean N Std.
Deviation Std. Error
Mean
Root Length Density (RLD) (mm/cm3)
Primary Pair 1 Circle 0-15 cm 1.25 24 1.41 0.29
Circle 15-30
cm 1.61 24 0.86 0.18
Pair 2 FS 0-15 cm 0.26 24 0.25 0.05
FS 15-30 cm 0.14 24 0.18 0.04
Secondary Pair 1 Circle 0-15 cm 2.14 24 1.31 0.27
Circle 15-30
cm 1.87 24 1.15 0.24
Pair 2 FS 0-15 cm 1.87 24 0.82 0.17
FS 15-30 cm 0.94 24 0.60 0.12
Fine Pair 1 Circle 0-15 cm 24.21 24 14.51 2.96
Circle 15-30 cm
11.26 24 7.72 1.58
Pair 2 FS 0-15 cm 23.54 24 11.75 2.40
FS 15-30 cm 5.59 24 2.76 0.56
Root Dry Matter (RDM) (mg/cm3)
Primary Pair 1 Circle 0-15 cm 10.20 24 12.57 2.57
Circle 15-30 cm
12.22 24 5.76 1.18
Pair 2 FS 0-15 cm 1.40 24 1.46 0.30
FS 15-30 cm 0.69 24 0.85 0.17
Secondary Pair 1 Circle 0-15 cm 1.72 24 1.33 0.27
Circle 15-30 cm
1.77 24 1.52 0.31
Pair 2 FS 0-15 cm 1.09 24 0.64 0.13
FS 15-30 cm 0.59 24 0.56 0.11
Fine Pair 1 Circle 0-15 cm 2.87 24 1.90 0.39
Circle 15-30 cm
1.18 24 0.76 0.15
Pair 2 FS 0-15 cm 2.23 24 1.11 0.23
FS 15-30 cm 0.52 24 0.32 0.07
Specific Root Length (SRL) (cm/g)
Primary Pair 1 Circle 0-15 cm 13.68 24 6.40 1.31
Circle 15-30 cm
13.16 24 3.93 0.80
Pair 2 FS 0-15 cm 16.62 24 10.78 2.20
FS 15-30 cm 14.96 24 21.58 4.41
Secondary Pair 1 Circle 0-15 cm 150.65 24 56.55 11.54
Circle 15-30 cm
125.44 24 48.86 9.97
Pair 2 FS 0-15 cm 186.49 24 46.63 9.52
FS 15-30 cm 316.92 24 407.97 83.28
Fine Pair 1 Circle 0-15 cm 930.49 24 470.20 95.98
Circle 15-30 cm
956.84 24 283.23 57.81
Pair 2 FS 0-15 cm 1085.53 24 226.89 46.31
FS 15-30 cm 1157.70 24 231.05 47.16
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Table 10. Paired t-test results for RLD, RDM and SRL at different soil depths
Class Paired Paired differences 95% confident interval of the
difference
t df difference
Sig (2-tailed)
Mean SD SE Lower Upper
Root Length Density
Primary C15 – C30 -0.35 1.50 0.31 -0.99 0.28 -1.15 23 0.264
FS 15 – FS 30 0.11 0.27 0.05 0.00 0.23 2.07 23 0.050*
Secondary C15 – C30 0.27 0.99 0.20 -0.15 0.69 1.33 23 0.196
FS 15 – FS 30 0.93 0.80 0.16 0.59 1.27 5.68 23 0.000*
Fine C15 – C30 12.95 10.50 2.14 8.51 17.38 6.04 23 0.000*
FS 15 – FS 30 17.95 11.50 2.35 13.10 22.81 7.65 23 0.000*
Root Dry Matter
Primary C15 – C30 -2.02 13.53 2.76 -7.73 3.69 -0.73 23 0.47
FS 15 – FS 30 0.72 1.33 0.27 0.16 1.28 2.65 23 0.01*
Secondary C15 – C30 -0.06 1.43 0.29 -0.66 0.55 -0.19 23 0.85
FS 15 – FS 30 0.49 0.74 0.15 0.18 0.81 3.27 23 0.00*
Fine C15 – C30 1.70 1.55 0.32 1.04 2.35 5.36 23 0.00*
FS 15 – FS 30 1.71 1.09 0.22 1.25 2.17 7.69 23 0.00*
Specific Root Length
Primary C15 – C30 0.52 7.19 1.47 -2.52 3.56 0.35 23 0.73
FS 15 – FS 30 1.66 21.48 4.38 -7.41 10.73 0.38 23 0.71
Secondary C15 – C30 25.21 54.70 11.16 2.11 48.31 2.26 23 0.03*
FS 15 – FS 30 -130.43 404.13 82.49 -301.08 40.22 -1.58 23 0.13
Fine C15 – C30 -26.35 515.66 105.26
-244.09 191.40 -0.25 23 0.81
FS 15 – FS 30 -72.18 247.60 50.54 -176.73 32.38 -1.43 23 0.17
*)mean differences are statistically significant at p<0.05
43
3. RLD, RDM and SRL at different plots (correspondent to Figure 13, Figure 14 and Figure 15respectively)
Table 11. Statistics of RLD, RDM and SRL at different plots
Root Class Soil Zone Plot N Group Mean
Std. Deviation
Std. Error Mean
Root Length Density (RLD) (mm/cm3)
Primary Circle BMP 12 1.24 0.81 0.23
REF 12 1.63 0.95 0.28
Frondstack BMP 12 0.18 0.20 0.06
REF 12 0.22 0.13 0.04
Secondary Circle BMP 12 2.02 0.91 0.26
REF 12 1.99 1.36 0.39
Frondstack BMP 12 1.64 0.68 0.20
REF 12 1.18 0.39 0.11
Fine Circle BMP 12 15.62 8.04 2.32
REF 12 19.85 12.26 3.54
Frondstack BMP 12 14.52 4.69 1.35
REF 12 14.61 7.83 2.26
Root Dry Matter (RDM) (mg/cm3)
Primary Circle BMP 12 9.85 5.63 1.62
REF 12 12.57 8.27 2.39
Frondstack BMP 12 0.96 1.11 0.32
REF 12 1.13 0.92 0.26
Secondary Circle BMP 12 1.88 1.34 0.39
REF 12 1.61 1.16 0.33
Frondstack BMP 12 1.08 0.51 0.15
REF 12 0.61 0.30 0.09
Fine Circle BMP 12 1.68 0.67 0.19
REF 12 2.37 1.55 0.45
Frondstack BMP 12 1.57 0.51 0.15
REF 12 1.19 0.66 0.19
Specific Root Length (SRL) (cm/g)
Primary Circle BMP 12 12.12 2.08 0.60
REF 12 13.54 3.28 0.95
Frondstack BMP 12 12.60 13.99 4.04
REF 12 23.36 9.11 2.63
Secondary Circle BMP 12 136.90 61.48 17.75
REF 12 128.73 34.94 10.09
Frondstack BMP 12 160.19 32.42 9.36
REF 12 204.74 42.67 12.32
Fine Circle BMP 12 939.27 389.39 112.41
REF 12 883.36 142.45 41.12
Frondstack BMP 12 935.64 132.42 38.23
REF 12 1251.71 135.63 39.15
44
Table 12. Independent T-test results between BMP and REF plots at different soil zones
Class Zone
Levene’s test for equality of
variance t-test for equality of mean
F Sig T Df Sig (2-tailed)
Mean diff
Std Error
95% confident interval of the
difference
Lower Upper
Root Length Density
Primary Circle 1.114 0.303 -1.083 22 0.29 -0.39 0.36 -1.14 0.36
Frondstack 2.965 0.099 -0.505 22 0.62 -0.04 0.07 -0.18 0.11
Secondary Circle 0.486 0.493 0.058 22 0.95 0.03 0.47 -0.95 1.01
Frondstack 3.303 0.083 2.03 22 0.06* 0.46 0.23 -0.01 0.93
Fine Circle 1.412 0.247 -1 22 0.33 -4.23 4.23 -13.01 4.55
Frondstack 4.039 0.057 -0.034 22 0.97 -0.09 2.63 -5.55 5.37
Root Dry Matter
Primary Circle 3.152 0.09 -0.944 22 0.36 -2.73 2.89 -8.72 3.26
Frondstack 0.644 0.431 -0.39 22 0.70 -0.16 0.41 -1.02 0.70
Secondary Circle 0.263 0.613 0.524 22 0.61 0.27 0.51 -0.79 1.33
Frondstack 2.294 0.144 2.761 22 0.01* 0.47 0.17 0.12 0.83
Fine Circle 4.24 0.052 -1.436 22 0.17 -0.70 0.49 -1.71 0.31
Frondstack 0.98 0.333 1.601 22 0.12 0.39 0.24 -0.11 0.88
Specific Root Length
Primary Circle 2.30 0.14 -1.27 22 0.22 -1.42 1.12 -3.75 0.90
Frondstack 1.73 0.20 -2.23 22 0.04* -10.76 4.82 -20.75 -0.76
Secondary Circle 6.97 0.02 0.40 22 0.69 8.18 20.41 -34.16 50.51
Equal variance not assumed+ 0.40 17.4 0.69 8.18 20.41 -34.81 51.16
Frondstack 1.30 0.27 -2.88 22 0.01* -44.55 15.47 -76.63 -12.47
Fine Circle 3.34 0.08 0.47 22 0.65 55.91 119.69
-192.32 304.14
Frondstack 0.00 0.96 -5.78 22 0.00* -316.07 54.72 -429.55 -202.60 +) used when levene’s test results are significant at p<0.05 *)mean differences are statistically significant at p<0.05
45
4. RLD, RDM and SRL at different fields (correspondent to Figure 16, Figure 17 and Figure 18 respectively)
Table 13. Group Statistic of RLD, RDM and SRL at different fields
Root Class Soil Zone Plot N Mean Std.
Deviation Std. Error
Mean
Root Length Density (RLD) (mm/cm3)
Primary Circle Good 12 1.33 0.78 0.23
Poor 12 1.54 1.01 0.29
Frondstack Good 12 0.16 0.16 0.05
Poor 12 0.23 0.17 0.05
Secondary Circle Good 12 1.99 1.29 0.37
Poor 12 2.01 1.01 0.29
Frondstack Good 12 1.21 0.49 0.14
Poor 12 1.61 0.63 0.18
Fine Circle Good 12 15.90 11.82 3.41
Poor 12 19.56 8.82 2.55
Frondstack Good 12 12.12 4.15 1.20
Poor 12 17.01 7.27 2.10
Root Dry Matter (RDM) (mg/cm3)
Primary Circle Good 12 9.95 5.63 1.62
Poor 12 12.47 8.31 2.40
Frondstack Good 12 0.66 0.75 0.22
Poor 12 1.43 1.09 0.32
Secondary Circle Good 12 1.86 1.27 0.37
Poor 12 1.63 1.24 0.36
Frondstack Good 12 0.73 0.48 0.14
Poor 12 0.95 0.47 0.13
Fine Circle Good 12 1.88 1.33 0.38
Poor 12 2.17 1.13 0.33
Frondstack Good 12 1.16 0.48 0.14
Poor 12 1.60 0.67 0.19
Specific Root Length (SRL) (cm/g)
Primary Circle Good 12 13.46 3.56 1.03
Poor 12 12.21 1.65 0.48
Frondstack Good 12 19.31 16.99 4.90
Poor 12 16.65 7.01 2.02
Secondary Circle Good 12 120.76 41.85 12.08
Poor 12 144.87 54.48 15.73
Frondstack Good 12 185.30 52.30 15.10
Poor 12 179.63 34.66 10.01
Fine Circle Good 12 846.44 180.92 52.23
Poor 12 976.19 362.92 104.77
Frondstack Good 12 1099.81 253.21 73.10
Poor 12 1087.54 161.94 46.75
46
Table 14. Independent T-test result of different between good and poor fields at different soil zones
Class Zone
Levene’s test for equality of
variance t-test for equality of mean
F Sig T Df Sig (2-tailed)
Mean diff
Std Error
95% confident interval of the
difference
Low up
Root Length Density
Primary Circle 1.874 0.185 -0.565 22 0.58 -0.21 0.37 -0.97 0.56
Frondstack 0.071 0.793 -1.029 22 0.32 -0.07 0.07 -0.21 0.07
Secondary Circle 0.026 0.873 -0.037 22 0.97 -0.02 0.47 -1.00 0.96
Frondstack 1.508 0.232 -1.726 22 0.10 -0.40 0.23 -0.88 0.08
Fine Circle 0.307 0.585 -0.86 22 0.40 -3.66 4.26 -12.49 5.17
Frondstack 4.736 0.041 -2.025 22 0.06 -4.90 2.42 -9.91 0.12
Equal variances not assumed+ -2.025 17.4 0.06 -4.90 2.42 -9.99 0.19
Root Dry Matter
Primary Circle 3.135 0.09 -0.87 22 0.39 -2.53 2.90 -8.53 3.48
Frondstack 1.603 0.219 -2.01 22 0.06 -0.77 0.38 -1.56 0.02
Secondary Circle 0.018 0.896 0.44 22 0.67 0.22 0.51 -0.84 1.29
Frondstack 0.087 0.77 -1.12 22 0.28 -0.22 0.19 -0.62 0.18
Fine Circle 0.006 0.937 -0.56 22 0.58 -0.28 0.50 -1.33 0.76
Frondstack 1.827 0.19 -1.84 22 0.08 -0.44 0.24 -0.93 0.06
Specific Root Length
Primary Circle 3.724 0.067 1.104 22 0.28 1.25 1.13 -1.10 3.60
Frondstack 8.363 0.008 0.502 22 0.62 2.66 5.31 -8.34 13.67
Equal variance not assumed+ 0.502 14.6 0.62 2.66 5.31 -8.67 14.00
Secondary Circle 1.851 0.187 -1.216 22 0.24 -24.11 19.83 -65.24 17.02
Frondstack 3.135 0.09 0.313 22 0.76 5.67 18.11 -31.89 43.23
Fine Circle 0.59 0.451 -1.108 22 0.28 -129.75 117.06
-372.52 113.02
Frondstack 7.402 0.012 0.141 22 0.89 12.27 86.77 -167.67 192.21
Equal variance not assumed+ 0.141 18.7 0.89 12.27 86.77 -169.52 194.07 +) used when levene’s test results are significant at p<0.05
47
5. RLD and RDM in ingrowth bag experiment (correspondent to Figure 19)
Table 15. Statistic of RLD and RDM between control and fertilizer treatment in ingrowth study
Treatment N Mean Std.
Deviation Std. Error
Mean
Root Length Density (RLD) (mm/cm3)
Control 6 3.9549 3.63027 1.48205
Fertiliser 6 2.5205 1.26594 0.51682
Root Dry Matter (RDM) (mg/cm3)
Control 6 24.9683 28.67768 11.70761
Fertiliser 6 22.5714 18.11913 7.3971
Table 16. Independent T-test results between control and fertilizer treatment in ingrowth study
Parameter
Levene’s test for equality of variance
t-test for equality of means
F Sig T Df Sig (2-tailed)
Mean diff
Std Error 95% confident interval of the difference
Low up
RLD 1.704 0.221 0.914 10 0.382 1.435 1.570 -2.063 4.932
RDM 0.349 0.568 0.173 10 0.866 2.397 13.849 -28.460 33.254