Abstract: Alpine grassland in northwest Sichuan, dominated by Fritillaria cirrhosa and subject to 3 or 10 years development, was compared with nearby uncultivated natural grassland (Control) to explore the effects of development on the soil phosphorus fractions. Soil phosphorus tests were performed using a modified Hedley method. It was found that after development the levels of total phosphorus (TP), water-soluble phosphorus (H₂O-Pi), active phosphorus (NaHCO₃-P), potentially active phosphorus (NaOH-P), stable phosphorus (Dil. HCl-Pi) and highly stable phosphorus (Conc. HCl-P) were significantly lower than those of Control plots, while residual phosphorus (Residual-P) levels were significantly increased. These changes were most pronounced in the 0-20 cm soil layer. After 10 years of development, the levels of TP, H₂O-Pi, NaHCO₃-P, NaOH-P, Dil. HCl-Pi and Conc. HCl-P decreased by 16.48%, 78.98%, 57.43%, 26.06%, 16.38%, and 10.87% respectively, while Residual-P levels increased by 40.08% (P<0.05). H₂O-Pi, NaHCO₃-P and NaOH-P changed to a greater extent than the others, indicating the higher the activity, the greater the loss. With increased time under development, the ratios of H₂O-Pi, NaHCO₃-P, and NaOH-P to TP significantly decreased, while the ratios of Dil. HCl-Pi, Conc. HCl-P, and Residual-P to TP increased. In the early stages of development (0-3 years), TP and various phosphorus fractions changed faster than at the later stages (3-10 years), indicating that the losses of the various phosphorus fractions mainly occurred in the early stages of development (0-3 years).

Key words: alpine meadow in northwest Sichuan, reclamation, soil phosphorus fractions