P肥施入土壤后的变化进程及对P淋失的影响

Change of P fertilizer After Application Into Soil and Its Influence on P Leaching Loss.

对施入不同剂量P肥的稻田土壤进行培养，测定不同时期土壤Olsen-P和CaCl2-P含量变化。结果表明，在施P量为100～1600kg·hm^-2条件下，200d时不同处理土壤Olsen-P含量降低量均接近于施P后的50％，不同施P量下土壤对Olsen-P的固定量均接近50％。表明在本试验施P量范围内该土壤仍未达到P吸附饱和，土壤对Olsen-P的固定量与施P量近似呈正比；当施P量低时，CaCl2-P含量低，且变化不明显；当施P量高于400kg·hm^-2时，CaCl2-P含量迅速增高。随着施P量提高，进入土壤缓效P库的比例降低，而进入速效P库和可溶性P库的比例增加，土壤对P的固定能力也逐渐降低，产生P损失的可能性增加，易于导致面源污染。预测结果表明，该土壤发生P素地表径流损失及在亚表层径流中P浓度猛增的Olsen-P含量“转折点”为81．3mg·kg^-1，与其对应的施P量约为524kg·hm^-2。可见，该土壤施P量一旦高于500kg·hm^-2，通过各种途径产生P损失的可能性增加。

Paddy soil samples applied with different rates of P fertilizer were incubated and examined for changes in contents of Olsen-P and CaCl2-P at different time periods. Results show that in 200 days, soil Olsen-P decreased by about 50% in all the treatments. When P application rate was low,the content of CaC12-P was low and did not varied much. But when P application rate exceeded 400 kg·hm^-2 ,the content of CaCl2-P rose rapidly. With the increasing P application rate,the proportion of the applied P entering into the P pool of residual P was decreasing, whereas those into the pools of dissolved P and Olsen-P were increasing, so the probability of P losing into water that may induce non-point pollution is increasing. The ＂change point＂ value of Olsen-P content that can indicate soil P loss into surface runoff and rapid increase in P content in subsurface drainage is 81.3 mg· kg^-1, and the corresponding P application rate is about 524 kg ·hm^-2. So, if P application is above 500 kg ·hm^-2 ,the possibility of soil P loss in different ways is increasing.