Effects of phosphatezation on organic phosphorus fractions and their seasonal variations and bioavailabilities of paddy soils in Hunan Province

Effects of phosphate fertilizer applications on soil organic phosphorus fractions and their seasonal variations and bioavailability were studied using the pot experiments. Five paddy soils derived from different parent materials in Hunan Province were used as test soils for the pot experiment．The results show that soil moderately labile organic phosphorus contents are increased under the P fertilizer application, while the fertilization has less effects soil labile organic phosphorus, moderately resistant organic phosphorus and highly resistant organic phosphorus. Soil organic P variation is mainly caused by the variation of moderately labile organic P under both P-unfertilization and P-fertilization, while the labile organic phosphorus and resistant organic phosphorus are not changed during rice growth and development stages. Available P was closely correlated with organic P in both P-unfertilized and P-fertilized soils, that is to say, the importance of organic P as a source of available P in soil were demonstrated. The bioavailability of soil organic P fractions during the growth periods of early rice in the pot experiment are in order of moderately labile organic P > moderately resistant organic P > highly resistant organic P > labile organic P, while the order for late rice is dependent on the growth and development stages of late rice.