Soil Characteristics and Management Effects on Phosphorus Sorption by Highland Plateau Soils of Ethiopia

Abstract

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 sorptoin 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.