Highly Weathered Soils and Tropical Environments: Opportunities and Constraints

1. Highly Weathered Soils and Tropical Environments: Opportunities and Constraints Russell Yost1, Bao-Shen Li2, Prof. Xiaolin Li2, ZuChao3 1Tropical Plant and Soil Sciences University of Hawai`i at Manoa Honolulu, Hawai`i 2China Agricultural University, Beijing, China 3Spice and Beverage Research Institute,Xinglong, Wanning, Hainan, China

2. 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

3. 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

4. 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.

5. 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

6. 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.

7. 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.

8. Effects of solution pH on pepper (Piper nigrum, L. roots, 4 days after treatments 7.0 5.5 3.5 Photos courtesy: Zu Chao,Spice and Beverage Research Institute, Hainan Island, China. 4.0

9. Effects of Al on root growth and water utilization Doss & Lund Agr. J. 67:193. Photo: Credit Dr. N.V. Hue and J. Hanson, University of Hawai`i Crotolariajuncea, L. on a high Al soil. Photo: Credit R. Yost, University of Hawai`i

10. 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

11. 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.

12. 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)

13. 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.

14. 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?

15. 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. Notso Effective

16. Alleviating toxicities: Liming Tisdale and Nelson: Soil Fertility and Fertilizers. Macmillan

17. Constraints to Productivity – Neutralization of Soil Acidity • Exchangeable (KCl-extractable Al) as a criterion for lime application (Kamprath, SSSAP 34:363.)

18. Constraints to Productivity – Neutralization of Soil Acidity • 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%. • Cochrane et al. An equation for liming acid mineral soils to compensate crop aluminum tolerance. Trop. Ag.57:133.

19. 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 (Brachiariadecumbens), tropical legumes: (Stylosanthesguianensis. Centrosemamacrocarpum, etc.). CIAT (Columbia) has a major breeding / selection program for acid tolerance.

20. 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.

21. Summary:Constraints • Acidity – Two options: Adjust the soil or Change the plant • Low nutrient content and capacity – variable charge soils • High P sorption capacity

22. 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.

23. Soil pH map of China Courtesy, Dr. Xinping Chen, China Agricultural University, Beijing, China

24. Thank you • Questions please!