Chemical composition of saturation paste extracts of a Fijian Oxisol after liming and repeated wetting and drying. (29)
Keywords:Aluminium, Anions, Cations, Calcium, Lime· Manganese, Phosphorus, Potassium, Soil acidity, Soil solution
AbstractThe effects of liming and incubating an Oxisol, either in a continuously moist state or subject to periodic drying and rewetting, on the nutrient composition of saturation paste extracts was investigated. The soil used was acid (pHH2O 4.5), had a relatively high soil organic matter content (9.6% organic C), and was typical of soils presently being cleared for sugar cane production. Liming resulted in an increase in the concentration of solution Ca2+ and a decrease in solution Mg2+ as the net negative charge on variable charge colloids increased. Concentrations of solution K+ decreased between pH 5 and 6 but then increased again. Liming markedly decreased concentrations of solution Al, Mn2 +, and SiO32-. Concentrations of solution phosphate increased between pH 5 and 5.8, then decreased as pH approached 6 before increasing again above pH 6.6. Levels of NO3- and SO4 2- in soil solution were raised as soil pH increased. Addition of phosphate to the soil increased concentrations of NO3, SO42-, and SiO32- in soil solution but reduced those of Al. Drying and rewetting increased pH by about 0.1 pH unit, decreased concentrations of solution Ca2+, Mg2+, Al, and SiO32-, and increased those of Mn2+, NO3-, and SO42-. The results demonstrated the complex pattern of change in nutrient concentrations in soil solution that can occur when a highly weathered tropical soil is limed. It is evident, however, that when soils such as this Oxisol are brought under cultivation, the major factors limiting production are Al toxicity and P and Ca deficiencies.