Highly Weathered Soils and Tropical Environments: Opportunities and Constraints

1. Highly Weathered Soils and Tropical Environments: Opportunities and Constraints Russell Yost Tropical Plant and Soil Sciences University of Hawai`i at Manoa Honolulu, Hawai`i

2. 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

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. • 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. Food Security • Desirable characteristics of food 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 input Conway’s Characteristics of agroecosystems. 1987; Cuc, Gillogly,Rambo. 1990. Agroecosystems of the Midlands of North Vietnam. East-West Center, Honolulu, HI

5. 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.

6. 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

7. 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

8. Effects of Al on root growth Translocation of Ca from roots to tops was decreased by Al: Blockage of the apoplastic pathway? Drawing: Wikipedia: Apoplast, Oct. 2012

9. Constraints to ProductivityAcidity – High soil Mn • Manganese toxicity Mn toxicity symptoms on cowpea Vignaunguiculata. L. on Wahiawa soil, Hawai`i (highly manganiferous soil). Normal leaf on left, Mn toxic leaf on the right.

10. 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.

11. 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

12. 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.

13. 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)

14. 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.

15. 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?

16. Constraints to Productivity – Ameliorating Soil Acidity or improving plant tolerance • 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-

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

18. 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

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

20. 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.

21. Constraints to Productivity – Ameliorating Soil Acidity or improving plant tolerance • 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)

22. Constraints to Productivity – Ameliorating Soil Acidity or improving plant tolerance • 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).

23. Constraints to Productivity – Ameliorating Soil Acidity or improving plant tolerance • 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 the rhizosphere. • Note: overliming above pH 6.0 can be serious.

24. Variation in soil reactivity to added phosphorus

25. 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

26. Prediction – case of P Crop property • 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 • BD = bulk density • placement = function of the fraction of row width fertilized

27. 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 • BD = bulk density • placement = function of the fraction of row width fertilized Soil factors

28. Prediction – case of P Soil management factors • 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 • BD = bulk density • placement = function of the fraction of row width fertilized

29. 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.

30. 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.

31. 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)

32. Thank you • Questions please!