Study on N use efficiency of chinese cabbage and nitrate leaching under open field cultivation

Fate of nitrogen fertilized on chinese cabbage(Brassica penkinensis) in open field of vegetable especially leaching loss was studied by lysimeter. The results showed that the yield of chinese cabbage application of organic manure (equivalent N 120 (kg/hm2)) was much higher than CK, and nitrate concentration no difference in lower soil profile, the leaching loss of nitrate from 1.3m depth of lysimeter was also not increased. Whereas, on the based of organic manure, the yield was not increased remarkably with chemical N fertilization and the VCR(value-cost ratio) was lower than 2.0. On the other hand, with increasing of N rate, the residue of nitrate in soil profile rose linearly and nitrate leaching loss from 1.3m depth lysimeter went up exponentially. For the three rates of chemical fertilizer N 375, 750 and 1125 (kg/hm2), nitrate leaching loss was N 16.6, 21.0 and 37.6 (kg/hm2),the apparent fertilizer N leaching loss rate was 2.3%, 1.8% and 2.6%, apparent fertilizer N use efficiency was 7.9%, 2.9% and 2.6%, apparent fertilizer N loss by air was 25.4%, 37.5% and 40.5%,respectively. These results indicated,the rate of N fertilization in open field of vegetable was much higher which might give higher pressure on environment.