Soil nitrogen balance in citrus orchards of the Three Gorges area in Chongqing

Based on data collected from farmer interviews and agricultural statistics database, the characteristics of N fertlizaion and surplus were studied in the Three Gorges area of Chongqing city. The result shows that the average N application rate is about 409.7 kg/ha, with a main source of compound fertilizers and urea. The N input rate through manure application is 76.51 kg/ha，with a main source of animal waste and manures. There is N surplus in the orchards, and the surpluses in Fengjie, Jiangjin and Yongchuan are relatively higher than other regions. The average N surplus is 363.9 kg/ha. There is positive correlation between N surplus and applied N rate in orchards, which indicates excessive N fertilizer input leads to the increase of N surplus. Further, with the increase of nitrogen surplus, total nitrogen of orchard soil tends to increase, while the ratio of soil C/N tends to decrease, indicating that the influence of nitrogen surplus on soil total nitrogen is higher than soil organic matter.