highly weathered soils and tropical environments: opportunities and constraints

Highly Weathered Soils and Tropical Environments: Opportunities and Constraints

Russell YostTropical Plant and Soil SciencesUniversity of Hawai`i at Manoa

Honolulu, Hawai`i

Goals – Opportunities and Constraints with Highly Weathered Soils

• Food security– High diversity of crop types (both annual and

perennial) relative to temperate crops Stability of production systems

• Environmental Health– Opportunity for perennial cover of soil

improved conservation

Highly weathered soils - Constraints

• Tropical environments: vs Temperate– Affecting Productivity, Stability, Resilience

• Climate and Weather– Day length is shorter and fewer days with optimal degree-day energy leading to lower

genetic potential of crop productivity.– Tropical, sub-Tropical environments often are characterized by high intensity rainfall,

which can challenge water and nutrient management and conservation• Greater soil weathering leading to:

– Nutrient insufficiencies, both less nutrients and less nutrient retention capacity – lower ECEC

– Element toxicities of Al and Mn

– Affecting Environmental Health• Nutrient leaching an increased concern

– Higher rainfall intensity, soils with lower water holding capacity• Conservation agriculture more difficult in annual cropping systems

– High intensity rainfall can challenge water and nutrient management and conservation

Food Security• Desirable characteristics offood production systems:

– “Productivity” – large quantities

– “Stability” – sustained production each year

– “Resilience” (previous “Sustainability”)• ability to restore production

– “Equitability” – all members of society have access.

– “Autonomy” – low dependence on outside inputConway’s Characteristics of agroecosystems. 1987; Cuc, Gillogly,Rambo. 1990. Agroecosystems of the Midlands of North Vietnam. East-West Center, Honolulu, HI

A structure for information in problem-solving soil constraints:

• Four components– “Diagnosis” – “Does a problem exist?” Is special

attention / management needed?– “Prediction” – “How to fix the problem?” What

does science say is needed?– “Economic Analysis” – “Is the proposed solution

(Prediction) feasible and profitable?”– “Recommendation” – “How to best inform /

transfer the above information to the grower, user, producer?” Assist in learning the process.

Yost et al., 2012. Efficient Decision-making in Agriculture. Intech Press.

Highly weathered soils --Characteristics affecting productivity

– Acidity – Al, Mn toxicity and the “soil acidity syndrome”

• Toxicities of Al, Mn, and H+

• Low nutrient content and retention (ECEC)– Phosphorus – usually high reactivity,

• Acid soil reactions – presence of alpha hydroxls, largely a consequence of mineralogy

• Calcareous soil reactions – still often an issue in Tropics – coastal, reef systems

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Effects of Al on root growth and water utilizationTable. Cotton grown on a Paleudult soil.

Root wt.

Subsoil pH % of total % of available water extracted

> 5.0 50 80 – 100

< 5.0 14 40 -- 70

Doss & Lund Agr. J. 67:193.

Crotolaria juncea, L. on a high Al soil. Photo: Credit R. Yost, University of Hawai`i

Photo: Credit Dr. N.V. Hue and J. Hanson, University of Hawai`i

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Effects of Al on root growthTranslocation of Ca from roots to tops was decreased by Al: Blockage of the apoplastic pathway?

Drawing: Wikipedia: Apoplast, Oct. 2012

Constraints to ProductivityAcidity – High soil Mn

• Manganese toxicity

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Mn toxicity symptoms on cowpea Vigna unguiculata. L. on Wahiawa soil, Hawai`i (highly manganiferous soil). Normal leaf on left, Mn toxic leaf on the right.

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Constraints due to Acidity – Mn toxicity

• Mn toxicity -- a balance between rate of Mn absorption vs. rate of plant growth– How to assess / compare the two rates?

• Relative Absorption Rate (RARMn) - Mn absorption per unit of Mn already contained in the plant.

• Relative Growth Rate (RGR) - Growth as a fraction of the existing growth (biomass). (See Radford, Crop Sci. 3:171-175. )

Relative Absorption Rate: Rufty, Agr. J. 71:638; Jocelyn Bajita, 2003, The Dynamics of Manganese Toxicity. Ph.D. Dissertation. University of Hawai`i.

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Constraints due to Acidity - Review

• Aluminum toxicity– Reduced root growth caused by impaired cell

division resulting in impaired growth and function. Probably resulting from DNA disruption

– Reduced Ca translocation to plant tops – apoplastic absorption pathway may be closed by Al.

– Reduced P sorption due to precipitation with Al in roots, free space, and cell walls

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Constraints due to Acidity - Review

• Manganese toxicity– No major effect on roots, top growth reduced– Concentrates in plant leaves, often margins leading to

crinkling– Appears to be nearly passive transport due to

transpiration (mass flow).– Not usually common at soil pH > 6.5, except in Hawai`i

on manganiferous soils

• Proton (H3O+) toxicity– Occurs but not usually serious unless soil pH is < 4.0 on

mineral soils.

Limited nutrient content and retention capacity

• Leaching losses may be greater: Higher rainfall intensity, lower soil silt content, less water retention by soil– Nutrient loss by leaching – higher in general– Ca, Mg

• Low retention capacity due to acidity– Variable charge soils (Al & Fe oxides) have

less charge in acid soil (pH dependent charge)

Constraints to Productivity – Low Nutrient Content and Capacity (low ECEC)

• Type of charge on soil minerals and dominant soils.– CEC= Sc*Cc example: Vertisols – CEC= Sc*Cv example: Oxisols & Ultisols – CEC= Sv*Cv example: Andisols

• S= specific surface (m2 g-1), c= constant, v= variable, C= surface charge density (esu m-2), (c=constant, v=variable) Uehara and Gillman. 1981. The Mineralogy, Chemistry, & Physics of Tropical Soils with Variable Charge Clays. Westview Press.

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Constraints to Productivity – Ameliorating Soil Acidity or improving plant tolerance

• Two options– Change the soil to meet the plant

requirements (traditional) – lime the soil• May alleviate toxicity locally, but maybe lime is

expensive or not available– Change the plant to match extensive soil

conditions – find adapted species / varieties• May alleviate toxicity, but does it alleviate problems

with low nutrient content?


• Change the soil to meet the plant requirements (traditional)– Neutralization of soil acidity:

3Al3+ + CaCO3 + 6H2O = 3Al(OH)3 + Ca2+ + HCO3 - + 2H+

| H2O + CO2↑ – The neutralization of acidity by lime (CaCO3 ) is usually based

on two properties:• Fineness of the material (% passing sieves: )

• Neutralization value relative to CaCO3 -

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Alleviating toxicities: LimingLiming material – Chemical quality CCE (Calcium Carbonate Equivalent)

CaCO3 (Calcite) 100

CaO (burnt lime) 179

CaMg(CO3)2 (Dolomite) 109

Ca(OH)2 136

MgCO3 119

CaSiO3 86

Limestone Quality – Physical properties

Limestone particle size (passing mesh) Effectiveness

Retained on 8 mesh 0

Passing 8 mesh retained on 60 mesh 50%

Passing 60 mesh 100%

Tisdale and Nelson: Soil Fertility and Fertilizers. Macmillan

Constraints to Productivity – Neutralization of soil acidity

– Neutralization of soil acidity:3Al3+ + CaCO3 + 6H2O = 3Al(OH)3 + Ca2+ + HCO3

- + 2H+ | H2O + CO2↑

– What matters most is the anion:• Al3+ + CaCO3 (lime) Al(OH)3 – adds Ca and increases pH – Very

effective• Al3+ + CaSO4 (gypsum) – adds Ca but doesn’t increase pH and

does complex with Al to reduce toxicity as complex Al – SO4 species. Not so effective

• Al3+ + CaSiO4 (silicate slag) – adds Ca and does increase pH. Effective

• Al3+ + Ca(NO3)2 (calcium nitrate) – adds Ca and but doesn’t increase pH. Not so Effective

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Constraints to Productivity – Neutralization of Soil Acidity

• Exchangeable (KCl-extractable Al) as a criterion for lime application (Kamprath, SSSAP 34:363.)

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Maize: (Zea mays, L.)

% Al saturation Soil pH % Relative Growth

68 4.4 18

44 5.1 98

27 5.6 100

Upland rice (Oryza sativa, L.)

% Al saturation Soil pH % Relative Growth

63 - 40 – 80

40 - 100

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• Calculating the amount of limestone necessary to neutralize toxic Al:– Cochrane et al. – used Al as a liming criterion,

but adjusted for variation in plant tolerance of Al:• Lime needed (cmolc kg-1)=1.5[Al – RAS(Al+Ca+Mg)

/100 ]– Where Al, Ca, Mg are KCl-extractable cations measured in

the original soil.– RAS – required %Al saturation of the particular crop. Varies:

e.g. RAS of mungbean=0, Cowpea=40, Maize=20, Upland rice=60, Sugarcane=75%.

Constraints to Productivity – Neutralization of Soil Acidity

- Cochrane et al. An equation for liming acid mineral soils to compensate crop aluminum tolerance. Trop. Ag.57:133.


• Option 2 – Change the plant for soil conditions – select a tolerant species– Select or change the plant to match extensive

soil conditions – find adapted species• Many plants tolerate high levels of toxic Al:

– Tea, azalea, pineapple, rye, cranberry, bermudagrass, star grass, buckwheat, peanut, Proteaceae family, pangola grass, brachiaria grass, rubber, blueberry, Norway spuce (Kamprath and Foy, 1985)

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• Option 2 – Change the plant for soil conditions – select a tolerant variety within a desired species– Select or change the plant to match extensive soil

conditions – find adapted varieties• Many plants have varieties with high acidity tolerance:

– Rice,alfalfa, tomato, soybean, ryegrass, snap bean, cotton, maize, sunflower, pea, sweetpotato, green algae, and among pathogens.

– Taro (Calisay, personal communication 1995)– Modern rice varieties can tolerate as much as 75% Al saturation

(CIAT, Colombia).

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• Option 2 – Change the plant for soil conditions– Select or change the plant to match extensive soil conditions –

find adapted species / varieties• Very successful approach: wheat, rice, soybean, sorghum• Problem: Does tolerance to Al provide tolerance to Mn?

– Not always: Ex. Desmodium ovalifolium – Al tolerant, but is highly susceptible to Mn toxicity.

May be related to avoid-ance mechanism. Organic acids in therhizosphere. • Note: overlimingabove pH 6.0 can beserious.

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Variation in soil reactivity to added phosphorus

Prediction – case of P

• Where: Preq=Predicted amount of P fertilizer• bc = Critical level of P for specified crop• b0 = Measured extractable P in the field• a2 = P buffer coefficient (PBC, increase in extractable P

per unit added P)• a1 = slow reaction coefficient• d = depth of incorporation(value of 10 to 20cm typical)• BD = bulk density• placement = function of the fraction of row width fertilized

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factorplacementBDdaabbc ***1*

20 Preq



per unit added P)• a1 = slow reaction coefficient• d = depth of incorporation• BD = bulk density• placement = function of the fraction of row width fertilized

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20 Preq

Crop property




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20 Preq

Soil factors




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20 Preq

Soil management factors

Summary:Constraints

• Acidity – Adjust the soil or Change the plant

• Low nutrient content and capacity – variable charge soils

• High P sorption capacity• Apply principles of Precision Agriculture:

The right kind, the right amount, at the right time in the right place.

Summary:Constraints

• Use a structure of information:– Diagnosis of problem – grower skill– Prediction of solution – scientific input– Economic evaluation -- scientific input– Recommendation to be given to the grower,

producer – Develop information tools: software, social media, depends on the grower producers.

Deep appreciation to:

• China Agricultural University,– Professor Fuzuo Zhang, China Agricultural

University, (Funding and Support)– Professor Xinping Chen, China Agricultural

University,– Professor Yuanmei Zuo, China Agricultural

University, Organization, Communication• Chinese Academy of Agricultural Science

hosts (CATAS)

Thank you

• Questions please!

highly weathered soils and tropical environments: opportunities and constraints

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