Soil characteristics and management effects on phosphorus sorption by highland plateau soils of Ethiopia
1999
Duffera, M. | Robarge, W.P.
Differences in crop and fertilizer management are known to influence P retention by soils. An experiment was conducted to study the effect of soil characteristics and management practices on P sorption behavior of the highland plateau soils of Ethiopia. Surface samples from two Vertisols, an Andisol, and an Alfisol were collected from farmers' fields, research station farms, and from non-cultivated-non-fertilized areas. Phosphorus sorption data were obtained by equilibrating 3-g soil samples in 30 mL of 0.01 M CaCl(2) containing various amounts of KH(2)PO(4). Inorganic P fractions were determined by the Hedley P fractionation scheme. There was little variation in P sorption among Vertisol samples of alluvial origin as a result of cultivation-fertilization practices. For soils of volcanic origin (Vertisol2 and Andisols), and the Alfisol, samples collected from farmers' fields sorbed more P than the non-cultivated and research station samples. Least amounts of applied P sorbed by the non-cultivated Andisol samples reflect the relatively large amounts of resin extractable P initially present in these soils and demonstrate that labile P initially present in the soil can influence subsequent P sorption. Stepwise regression analysis of the P sorption data showed that resin P accounts for 81% of the variation in P sorption at 0.2 mg P L(-1) in solution. The highest amount of P was sorbed by samples collected from farmers' fields and was mainly due to the practice of continuous cropping with minimal P fertilization, which depletes labile P, and therefore requires higher levels of P fertilization for optimum crop yield.
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