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Abstract

Soil phosphorus is a major nutrient that controls plant growth and development in agricultural ecosystems. Its availability to plants is mainly caused by absorption and desorption of phosphate by Al- and Fe-(hydro) oxides. It is expected that changes of land use modify the distribution of soil P among the various P-pools (P-total, P-labile, P-organic). The aim of the study was to measure the different soil P-pools and the phosphate desorption kinetics under different land-use systems. Four different land-use systems were studied: silvopastoral and arable land cultivated for more than 30 years, and silvopastoral land converted to grassland and to arable land 5 years ago. The study was carried out in northeast of Brandenburg in Germany. Samples were taken from two layers: 0 10 cm and 10 20 cm soil depth. Different P forms were determined by a fractionation procedure and the P desorption kinetics were measured by the flow-through reactor technique over a long term. Total P content for all study sites was comparable; however the highest value was measured in the 30- year-old silvopastoral system with 685 mg kg-1 and 728 mg kg-1 at 0 10 cm and 10 20 cm depth, respectively. The labile pool of phosphorus was higher for the silvopastoral system than for arable land cultivated for more than 30 years and for arable land after 5 years of conversion. The results have shown that the 30-year-old silvopastoral system contained larger amounts of labile P. The P desorption kinetics considered as a dynamic measurement are described by a first-order-reaction model to distinguish between varying P pools in soils.