Effects of deforestation on phosphorus pools in mountain soils of the AlayRange, 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 eff ects of deforestation and pasture establishment on the concentrations, form s and turnover rate of soil P in mountain soils of the Alay Range, Khyrgyzi a. 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 th e structure of alkali-soluble P forms. In the A horizons of the forest soil s, total soil P concentration was 1093 mg kg(-1), organic P (P-o) represent ing 46% of the total P. Deforestation followed by pasture establishment not only increased significantly (P<0.01) the total P concentration (1560 mg k g(-1)) but also the contribution of P-o to total P was increased by 17%. Pa sture soils had significantly higher P pools than forest soils except highl y labile inorganic P (P-i NaHCO3) and primary P-i (P-i HCldil) Both in fore st and pasture soils stable P increased with decreasing particle size (coar se sand 50%, clay 80% of total P) and primary P decreased with decreasing p article size. Phosphate monoesters and diesters represented 80% of P identi fied by P-31 NMR. Low monoester to diester ratios in the alkali extracts of forest and pasture soils indicate low microbial activity. This is consiste nt with high C/P-o ratios and high stable P-o concentrations in the fine ea rth of forest and pasture.