The objective of this study is to provide scientific guidance for optimizing agricultural field nitrogen management that is based on the evaluation of current nitrogen application practice in Jiangsu Province, China, in 2000. The agricultural nitrogen models, consist of the soil mineralization model, the organic manure nitrogen releasing model, and the nitrogenous fertilizer use efficiency model. These models combined with the geographic information system technique were used to describe the spatial variability of nitrogen released from soil and organic manure and to identify its contributing factors. The comparison of the nitrogen fertilizer amount required by croplands, which was simulated by the models with the actual nitrogen fertilizer applied rate, was used to evaluate the current nitrogen application. The results showed that nitrogen was excessively applied in 71.8% croplands, given that the actual crop yield was desired. The excessive nitrogen amounted to 760 kiloton, accounting for 41.5% of the total nitrogen applied. Given that the actual highest yield was desired, nitrogen was reduced in 64.3% croplands. The total shortage of nitrogen was about 800 kiloton. Low use efficiency of nitrogen fertilizer was found in Taihu Lake area, Nanjing-Zhenjiang hilly area, and Xuzhou area, whereas the east beach area of Jiangsu showed an obvious deficiency of nitrogen fertilizer inputs. A balance of nitrogen fertilizer in Jiangsu croplands between excessive and deficient application areas would greatly benefit economic and environmental advantages.
