Effects of deforestation on phosphorus pools in mountain soils of the Alay Range, Khyrgyzia

The amount, quality and turnover of soil P is heavily influenced by changes in soil management. The objective of this study was to investigate the effects of deforestation and pasture establishment on the concentrations, forms and turnover rate of soil P in mountain soils of the Alay Range, Khyrgyzia. A sequential extraction was applied to distinguish soil P pools. We used particle-size fractionation to follow the dynamics of different P pools in soils under forest and pasture and P-31-NMR spectroscopy to investigate the structure of alkali-soluble P forms. In the A horizons of the forest soils, total soil P concentration was 1093 mg kg(-1), organic P (P-o) representing 46% of the total P. Deforestation followed by pasture establishment not only increased significantly (P<0.01) the total P concentration (1560 mg kg(-1)) but also the contribution of P-o to total P was increased by 17%. Pasture soils had significantly higher P pools than forest soils except highly labile inorganic P (P-i NaHCO3) and primary P-i (P-i HCldil) Both in forest and pasture soils stable P increased with decreasing particle size (coarse sand 50%, clay 80% of total P) and primary P decreased with decreasing particle size. Phosphate monoesters and diesters represented 80% of P identified by P-31 NMR. Low monoester to diester ratios in the alkali extracts of forest and pasture soils indicate low microbial activity. This is consistent with high C/P-o ratios and high stable P-o concentrations in the fine earth of forest and pasture.