Fractionation and availability of phosphorus in acid soils of Hagereselam, Southern Ethiopia under different rates of lime.

Background: Phosphorus (P) availability is commonly assumed to limit productivity in many tropical soils, yet there is relatively little information on the phosphorus chemical forms, distribution, and transformations that P undergoes in Ethiopian soils. We used a sequential fractionation scheme to assess phosphorus fractions of acid soils of Southern Ethiopia. The study area called Hagereselam is characterized by high soil acidity, and the availability of P in the study area is relatively low. As crop production in Ethiopia is dominated by low external input practices, native P remains the main contributor to plant P nutrition in many locations. Result: Although the total P concentration is 829.7 mg kg, the organic P content was relatively low (58 mg kg) and constituted on average less than 7% of the total P. The ratio of organic carbon to organic P was generally greater than 240, suggesting the potential for immobilization of P. The Al + Fe-associated P was the dominant inorganic P pool. The majority of the P occurred in recalcitrant form (568.3 mg kg). Readily available, exchangeable phosphate, as extracted by anion-exchange resin membranes, was present in very low concentrations (3.3 mg kg); moreover, labile P accounted for less than 2% (9.9 mg kg) of the total soil P. Conclusion: Lime was used as a reclamation material for acid soils, and the application of lime significantly affected the different P fractions and was involved in the transformation of P fraction. Organic P forms were significantly lower for higher levels of lime application, suggesting that lime amendment enhanced organic P decomposition. Moreover, application of lime increased Ca-P and decreased Al + Fe-P for acid soils. [ABSTRACT FROM AUTHOR]