Dynamic Change of Soil Phosphorus Pool in Paddy Soil Under Fixed Position Experimental Conditions

An experiment was carried out to study the change of the content and forms of phosphorus in a purple paddy soil under 22 years-localized fertilization. The results have shown that compared to the status before the experiment, the total phosphorus, available phosphorus and various morphologies of inorganic phosphorus had all increased to a certain degree in the soils with long-term application of chemical phosphate and treated by application of the combination of organic fertilizer and chemical fertilizer, among which the soil treated by pig manure+NPK (M+NPK) had increased the most and the content of available phosphorus had increased by six times; while the available phosphorus, total phosphorus, and various morphologies of inorganic phosphorus had reduced in the soil without application of soil (CK) and that only applied by nitrogenous fertilizer, among which the contents of available phosphorus had reduced by 51.1% and 53.5% respectively. The distributions of profiles treating inorganic phosphorus like Ca₂–P, Al–P, Ca₈–P, and O–P were all rather similar to each other, and all had reduced rather quickly at 20–60 cm but gradually had no significant changes or had a slightly rising trend at 80–100 cm plus that the phenomenon of the content of Fe–P in lower layer higher than that in the arable layer even appeared. It had been shown by relevant analysis that the contribution of various groups of inorganic phosphorus to purple soil was Ca₂–P > Al–P > Ca₈–P > Fe–P > Ca₁₀–P > O–P. Long-term of combined application of organic and inorganic fertilizers could significantly increase the accumulation of phosphorus in soil and be liable to render the phosphorus to move downwards.