Study on Fertility of Vegetable Soil and Controlling Technique for Pollution of Nitrate in Vegetable Crops I.The Phosphate Status and Fractionation of Inorganic Phosphate in Some Vegetable Soils of the Suburbs of Changsha

To ascertain phosphate status of vegetable soils in the suburbs of Changsha, the mixed soils of plough layer and profile soils were studied by investigation and analysis.The results are as follows,1) The contents of total P and available P in vegetable soils were much higher than the agricultural sails and natural soils.Total P varied from 0.78 to 2.72 g/kg and its average was 1.72 g/kg.The available P varied from 12.82 to 286.7 mg/kg and its average was 156.7 mg/kg.2) The main phosphate fraction was inorganic P in vegetable soils, and up to 74.96%～95.86% of total P.It varied from 584.7 to 2 607.5 mg/kg and its average was 1 495.7 mg/kg.3) The inorganic phosphate fractions varied with parent material in vegetable soils.Soils that derived from the quaternary red clay, had more O-P,Fe-P,Al-P was less, while the soil that derived from rive alluvium had more Fe-P,Al-P and O-P was less.4) The correlation analysis showed that the main resources of available P was inorganic P,and the correlation coefficient between available P and Ca2-P,Ca8-P,Al-P,Fe-P was significant.