Effects of long term fertilization on phosphorus pools and forms in yellow paddy fields of southern China

Based on data collected in a long term fertilization experiment in yellow paddy fields in Fujian, effect of different long-term fertilization on soil available phosphorous(AP), total phosphorus(TP) and phosphorus component was studied. The results show that the contents of AP and TP are increased with the age of experiment in the fertilization treatments in the double-rice system and decreased in the single-rice system, while the contents of the no- fertilizer treatment (CK) are decreased in both double and single rice terms, especially the content of AP which is reduced by 64-9%. In the 26th year of the fertilization experiment, compared with CK, the contents of total inorganic P(TIP), total organic P(TOP) and TP are increased markedly (P 0.01) by 46.2%-114.2%, 16.0%-41.8% and 29.2%-73.8% in NPK, NPKM and NPKS, respectively, and the highest growth rate is found in the treatment of NPKM. Compared with the soil before the experiment, the content of soil TIP in the CK treatment is decreased while the content of TOP is increased, and the Al-P component is decreased fast, and the increased rate of moderate stability component is the highest in TOP. The ratios of Al-P and Ca-P to TP in the fertilization treatments are higher than those of CK, while the ratio of organic phosphorus to TP is lower. There is a decline trend of the ratio of TIP to TOP in all experiment treatments, and the ratios in the fertilization treatments are higher than that of CK, especially the treatment of NPKM. In addition, there is a positive correlation between the ratio of TIP to TOP and the content of organic matter (P 0.01). The contents of organic phosphorus in yellow paddy soil have increasing trends with experiment age in both the fertilization treatments and CK. The effect of the NPKM treatment on increasing the contents of AP, inorganic phosphorus and organic phosphorus are the most significant among different treatments, but the differences among the contents of the inorganic phosphorus and organic phosphorus components in the treatments of NPKS and NPK are not significant. Under the cultivation patterns of double and single cropping rice in yellow paddy fields, the highest crop yields are achieved when the contents of available phosphorus are 17.56 mg/kg and 16.94 mg/kg, respectively.