Based on 13 years of long-term positioning experiment,and the split plot design was adopted.The main treatment was the roots of grass coverage and clearing,The secondary treatment was four fertilizer treatments,including no fertilizer (CK),single application of organic fertilizer (M),combined application of nitrogen,phosphorus and potassium (NPK) and combined application of organic and inorganic fertilizer (MNPK).The modified Hedley phosphorus classification method was used for extraction and determination of various phosphorus forms.The results showed that the contents of various phosphorus forms in 0—20 cm and 20—40 cm layers of calcareous soil were mainly D.HCl—P and residue—P,and the ratio of water-soluble phosphorus (H₂O—P) to inorganic phosphorus sources of sodium bicarbonate (NaHCO₃—Pi) was low.After 13 years of grass mulching and different fertilization treatments,the combined application of organic and inorganic fertilizers under grass mulching conditions increased the content and proportion of inorganic phosphorus in soil,and the content and proportion of residual phosphorus in 0—20 cm and 20—40 cm soil layers reduced from 68.5% and 66.1% to 75.8% and 69.7%,respectively,the proportion of residual phosphorus decreased from 26.8% and 27.0% to 18.3% and 23.5%,respectively.The combined application of organic and inorganic fertilizers under grass mulch could significantly increase the contents of available P and inorganic P in soil and the proportion of H₂O—P and NaHCO₃—Pi active P in soil.The combined application of organic and inorganic fertilizers under grass mulch could increase the content of active P in soil and maintain a high proportion of available P pool,which was an important measure to improve the utilization rate of P fertilizer in apple orchard.It is very important to ensure the high yield of apple and the efficient utilization of phosphorus fertilizer resources in this area.