Influence of long-term localized fertilization on phosphorus forms in paddy soil

An experiment was carried out to study the change of the content and forms of phosphorous (P) in a red paddy soil under 21 years—localized fertilization. The result showed: both organic P and available P content decreased without fertilization. The content of organic P under combining application of organic and inorganic fertilizer was higher than those under no fertilization and solo chemical fertilizer application. Combining application of organ-inorganic fertilizer not only could increase the content of Al-P, Fe-P and Ca-P in red paddy soil, but also significantly improve the activation of O-P, indicating that combining application of organic - inorganic fertilizer could enhance the content of both soil organic P and available P. Furthermore，our results showed that applying additional P had negligible effect on rice yield when the content of the available phosphorus in the red paddy soil was around 20mg/kg.