[Influence of long-term fertilization on phosphorus fertility of calcareous soil II. Inorganic and organic phosphorus].

By the Jiang-Gu inorganic phosphorus fractionation method and the Bowman-Cole organic phosphorus fractionation method, this paper studied the forms and compositions of inorganic and organic phosphorus in 0-100 cm layer of calcareous soil after 23 years located experiment. The result showed that the content of inorganic phosphorus was in the order of treatment animal manure > fallow > chemical fertilizer > low rate straw > high rate straw > medium rate straw > no fertilizer. The IPi value of inorganic phosphorus forms in different fertilizer treatments had the following characteristics: a) it was relatively low for Ca2-P, Ca8-P and Al-P, but relatively high for Ca10-P, Fe-P and O-P; b) comparing with no fertilizer treatment, treatments animal manure and fallow had a notably high IPi value of Ca2-P, Ca8-P and Al-P and a low IPi value of Ca10-P, Fe-P and O-P; while treatment chemical fertilizer had a high IPi value of Ca2-P, Ca8-P, Al-P and O-P, but a low IPi value of Ca10-P and Fe-P; c) as for available phosphorus source (Ca2-P, Ca8-P and Al-P), their content was higher in treatment animal manure than in treatment chemical fertilizer, and higher in treatment chemical fertilizer than in treatments straws. A combined application of straw and chemical fertilizer could increase soil organic phosphorus content notably. Applying animal manure could increase the content of all organic phosphorus forms, while applying chemical fertilizer could promote the transformation of soil resistant organic phosphorus to labile and medium labile organic phosphorus. No fertilizer treatment had a relatively lower content of labile and medium labile organic phosphorus, but a relatively high content of resistant organic phosphorus. For treatment fallow, it had a relatively low content of soil organic matter and organic phosphorus, but a relatively high content of labile and medium resistant organic phosphorus.