The effects of Chinese cabbage N application rate on Chinese cabbage yields, nitrogen utilization, nitrate contents, and nitrate nitrogen accumulation in soil were studied under potato-Chinese cabbage double cropping system in Hetao irrigated area of Inner Mongolia with 5 N application rates at Chinese cabbage planting season. The results showed that the yields and the double cropping net economic returns were the highest with the Chinese cabbage N application rate of 120 kg.hm -2; the double cropping system N accumulation and N recovery ratio were enhanced at the total N application rate from 225 kg.hm -2 to 405 kg.hm -2, compared with that of the conventional mono potato production in the open field at the N application rate of 225 kg.hm -2; the nitrate contents in Chinese cabbage and the nitrate accumulations within 0-160 cm soil profiles were increased with the increscent N applied rates. At the Chinese cabbage N application rate was ?120 kg.hm -2, the nitrate contents in Chinese cabbage reached a high level, and the nitrate accumulations within 0-160 cm soil profiles were ?162 kg.hm -2, hence the risk of nitrate contamination in underground water was increased for autumn irrigation. Reasonable N application rate had an effective effects on reducing nitrate contamination in groundwater, reducing nitrate content in Chinese cabbage, and increasing net economic return.
