Dynamics and availability of soil soluble organic phosphorus in a long-term fertilization experiment

Based on the long-term(1989 to 2004) field fertilization experiment in calcareous fluvo-aquic soil with crop rotation of winter wheat and summer maize,three extractants(water,NaHCO3,Mehlich 3) and the method of ICP-AES were used to study the dynamics and availability of soil soluble organic phosphorus as well as the effect of different fertilization treatments on organic phosphorus availability.The results showed that: 1)Soil soluble organic phosphorus values maintained at the wondrously low level as background soil without applying phosphorus fertilizer;while soil soluble organic phosphorus contents increased significantly with the application of organic manure,followed by combined application of organic manure and inorganic fertilizer.However,application of inorganic fertilizer alone showed a relatively lower effect;2)Applying inorganic fertilizer phosphorus without nitrogen(PK)inorganic phosphorus accounted for more than 90% of total phosphorus extracted by three extractants;3)Water,NaHCO3 and Mehlich 3 extractable organic phosphorus accounted for 18.8%,14.5% and 8.8% of homologous extractable total phosphorus,respectively;4)Water,NaHCO3 and Mehlich 3 extractable organic phosphorus were positively correlated with accumulated phosphorus in the shoot of crops and soil organic matter,and showed high availability especially in phosphorus-sterile soils,which demonstrated that organic phosphorus was an important source of soil available phosphorus pools.