The Loss Of P And N From Soil In The System Of Rice-Wheat Rotation In The South Of Jiangsu Province

Both field and lab experiments in two sites, Yixing and Changshu, Jiangsu provincewere done to study the transport of P and N from soil to water in the system of rice-wheatrotation in the south of Jiangsu province. The results obtained were as follows:Application of P fertilizers could increase the concentration of P in the surface waterof paddy field. The concentration of dissolved and total P were 25.66 mg / L and 86.36mg / L respectively when 300 kg P/hm~2 were applied to soil in the sample collected at thefirst time while they were 0.07mg / L and 0.17mg / L in the soil of control (without Papplication). The concentration of P was gradually decreasing with the time. Theconcentrations of N in the surface water of paddy field were not affected by different Pfertilizer application rates.The quantities of P vertical leaching in Yixing site and Changshu site were 3.77kg/hm~2 and 4.84 kg/hm~2 respectively while N vertical leaching were 60.25 kg/hm~2 and80.07 kg/hm~2 when fertilization was done in a common way. The P lateral leaching losswas 0.9 g/m~2 and N was 32.0 g/m~2.P and N movement in soil were investigated by using of KH2 32PO4 and CO (15NH ) 2tracker method. There was 46% and 42% of total 32P still retained in the layer 0-5cm ofsoil in Yixing site and Changshu site, respectively and 46.1% and 42.9% of total 15N stillretained in the layer 0-5cm of soil one month after fertilization.The concentration of P in runoff water of rice and wheat season was increasing withthe application rates of P fertilizer thus leading a same trend of the quantities of P losswith runoff. The quantities of P loss with runoff were 462 g/ hm~2 in rice season and 734g/ hm~2 in wheat season when the soil were fertilized as 30 kgP/hm~2 in rice season and 20kgP/hm~2 in wheat season which were near to the local traditions, respectively. The N losswas 4000g/ hm~2 in rice season and 2000 g/ hm~2 in wheat season when the soil werefertilized as 300 kgN/hm~2and 150 kgN/hm~2. The yields of rice and wheat were notaffected by the rates of P fertilizer application when the fertilizer was more than 30...