Effect of long-term fertilization on the forms of inorganic phosphorus in calcareous fluvo-aquic soil

A new soil inorganic phosphorus fractionation method proposed by Jiang Bofan Gu Yichu(1989) was adopted to study the effect of long term fertilization on transformation of inorganic phosphorus in surface soil, distribution of inorganic phosphorus in soil profile The result indicated that plant mainly used inorganic phosphorus in forms of Ca8-P-Al P-Fe P and Ca2-P in surface soil and subsoil within 30～50cm when soil phosphorus was depleted Only in excessive P depletion could plant use Ca10-P O-P was the most stable form of inorganic phosphorus that plant could not use When soil phosphorus accumulated by application of phosphorus fertilizer, the accumulated phosphorus mainly transformed into the forms of Ca10-P and O-P that plant can hardly use While combine use of chemical fertilizer and organic manure, the accumulated phosphorus mainly transformed into readily available forms of Ca2-P and Ca8-P Not only the inorganic phosphorus pool of Ca8-P-Al P-Fe P and Ca2-P were enlarged by combine use of chemical fertilizer and organic manure, but also the contents of these forms of inorganic phosphorus increased in the soil below surface, and as the application of organic manure increased, the deeper depth of soil profile was affected In our study condition, the effect of fertilization on the contents of inorganic phosphorus forms wouldn't exceed 50cm below the surface soil The contents of O-P and Ca10-P in the subsoil were little affected by fertilization, their contents were mainly affected by soil texture O-P (and Fe-P also) generally accumulated in clay layer in the soil profile, on the contrary, Ca10-P accumulated in sandy soil But the other two forms of Ca-P were not found accumulating in Sandy soil in the soil profile