Effect of surface soil nitrogen pool on productivity of permeable paddy soil in Taihu Lake region of China

Twenty-four years(1980～2004) field experiment in Taihu Lake region of China has shown that rice yield is significantly influenced by soil nitrogen.No fertilization and application of P,K fertilizers reduce soil nitrogen pool,while the application of fertilizers with N(N fertilizer;N,P fertilizers;N,K fertilizers;N,P,K fertilizers)slowly increases the soil nitrogen pool.Unlike inorganic nitrogen,organic nitrogen incorporation(straw manure)facilitates soil nitrogen pool build-up.In contrast with zero-fertilizer treatment,yield increase rate under NPK and organic fertilizer incorporation treatments is the highest,35.94%.With nitrogen application,the relationship between total surface soil nitrogen and rice yield changes from one of significant to an insignificant level.