Highly Weathered Soils and Tropical Environments: Opportunities and Constraints

Russell Yost1, Bao-Shen Li2, Prof. Xiaolin Li2, ZuChao3

1Tropical Plant and Soil SciencesUniversity of Hawai`i at Manoa

Honolulu, Hawai`i2China Agricultural University, Beijing, China

3Spice and Beverage Research Institute,Xinglong, Wanning, Hainan, China

Goals – Opportunities and Constraints of Managing Highly Weathered Soils

• Food security opportunities:– A very high diversity of crop types (both

annual and perennial (e.g. rubber, banana, pineapple and pepper)) relative to temperate crops (maize, wheat) Stability of production systems

• Environmental Health– Opportunity for perennial cover of soil

(perennial crops) 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 - max yields of maize and wheat are less.– 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

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”

• Low pH• Toxicities of Al, Mn, and H+

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

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

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

Example: Banana grown on a red, acid soil, pH 4.5-5.0

Photos curtesy: Bao-Shen Li, Prof. Xiaolin Li, China Agricultural University, Beijing.

Example: Banana grown on a red, acid soil, near Nanning, China, pH 4.5-5.0

Photos curtesy: Bao-Shen Li, Prof. Xiaolin Li, China Agricultural University, Beijing.

7.0 5.5

4.0

3.5

Effects of solution pH on pepper (Piper nigrum, L. roots, 4 days after treatments

Photos courtesy: Zu Chao, Spice and Beverage Research Institute, Hainan Island, China.

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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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Constraints due to Acidity - Review

• Aluminum toxicity– Reduced root growth caused by impaired cell

division resulting in impaired growth and function, especially in roots. 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?

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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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

• 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.

Constraints to Productivity – Ameliorating Soil Acidity or improving plant tolerance

• Option 2 – Using plants / crops well adapted to acid soils: The approach widely used in countries with land within the tropics: Malaysia, Indonesia, Thailand, Central and Northern South America, Central part of Africa.

• Major examples: cassava:Thailand, oil palm:Malaysia, rubber:Indonesia, sugar cane, almost everywhere, forage grasses Central and South America (Brachiaria decumbens), tropical legumes: (Stylosanthes guianensis. Centrosema macrocarpum, etc.). CIAT (Columbia) has a major breeding / selection program for acid tolerance.

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Constraints to Productivity – Ameliorating Soil Acidity or improving plant tolerance

• Option 2 – Using plants / crops well adapted to acid soils: The approach widely used in countries with land within the tropics: South America:

• Wheat: Brazil (pH can be as low as 4.5 - 5.0)• Upland rice: Columbia, Brazil (pH can be as low as

4.5 - 5.0)• CIAT (Columbia), and CIMMYT (Mexico) major

breeders of acid tolerant crops.

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Summary:Constraints

• Acidity – Two options: Adjust the soil or Change the plant

• Low nutrient content and capacity – variable charge soils

• High P sorption capacity

Summary:Solving Crop production problems on acid soils:

• Use a structure of information:– Diagnosis of problem – improve grower skill– Prediction of solution – improve scientific

knowledge, new solutions– Economic evaluation -- Evaluating the economic

factors– Recommendation to be given to the grower,

producer – Information dissemination: software, social media, depends on the grower producers.

Soil pH map of China

Courtesy, Dr. Xinping Chen, China Agricultural University, Beijing, China

Thank you

• Questions please!