Effects of low rate nitrogen application on Brassica chinensis growth and Nlosses

Understanding N-cycling in the soil-plant-atmosphere system is essential to maximize nitrogen use efficiency (NUE) and optimize nitrogen budget for crop production. Most researches on N loss and its environmental consequence mainly focused on the soil cultivated with field crop, however, few researches were carried out on the vegetable field. This study aimed to the effects of N fertilization on the fate of nitrogen and green cabbage (Brassica chinensis) growth. A field and a microplot experiment were combined to investigate the changes of green cabbage yield, NUE and nitrogen losses subjected to a low rate application of N fertilize. Labeled 15N technique, enclosure method, and acetylene inhibition-soil core incubation technique were used to measure total nitrogen loss, ammonia volatilization, denitrification loss and nitrous oxide emission, respectively. Results showed that yield and N uptake capacity of green cabbage increased significantly due to the application of nitrogen fertilizer. NUE was 46.8% and 39.4% at rate of N 75 and 150 kg/ha, respectively. The increase of ammonia volatilization was negligible mainly due to low soil pH (5.38). Denitrification loss(N 4.34 kg/ha)and N2O emission (N 2.65 kg/ha) in the soil without nitrogen supply were rather high, and it was not affected by the application of nitrogen. Total recovery of applied N at rate of 75 and 150 kg N/ha was 103% and 91.3%, respectively. The majority of residue 15N concentrated on 0-20cm layer, indicating fertilizer nitrogen losses were small, which coincided with the results of low ammonia volatilization and denitrification losses.