Fertilizer Application and Nutrient Balance Under Different Cropping Systems in Taihu Lade Region,Jiangsu Province

To investigate contribution of agricultural non-point source pollution to eutrophication of the waterbody of Taihe Lake,Yixing,Liyang and Wuzhong of Suzhou,typical areas of the Taihu Lake region,were chosen as subjects for study on fertilizer application and nutrient balance under two different cropping systems,i.e.rice-wheat and rice-rapeseed.It was found that under the two cropping systems,an annual total of 556.2 and 488.0 kg·hm^-2 of N fertilizers was applied,respectively,bringing N surplus rate up to 100.2% and 62.5%,separately.For the rice seasons, an average of 298.0 kg·hm^-2 of N fertilizer was applied and significantly higher than the average of the wheat seasons (299.1 kg·hm^-2) and of the rapeseed seasons (218.9 kg·hm^-2).The annual P fertilizer application rate was 117.6 kg·hm^-2 in the rice-wheat system and 116.7 kg·hm^-2 in the rice-rapeseed system,and the the P surplus rates of the two systems weere quite low,being 9.0% in the former,and -7.4% in the latter.The annual K fertilizer application rate was the least among the three macro-nutrients,being 107.3 and 105.3 kg·hm^-2 for the two systems,separately.As a result,both systems sufered K deficit,being over 50%.Obviously,in the two cropping systems,the application rate of nitrogen is much higher than that of phosphate and potassium,resulting in great N surplus;P application is quite reasonable and almost adequate to maintain soil P balance; and K application is the least in rate,leading to serious K deficit.