Nitrogen use efficiency and N losses from Chinese cabbage grown in an open field

Understanding of N-cycling in the soil-plant-atmosphere system is a prerequisite to maximize nitrogen use efficiency(NUE) and to develop optimized nitrogen budget for crop production.However,information on direct measurement and evaluation of N loss via ammonia volatilization,nitrate leaching,denitrification and NUE in vegetable fields is scarce.The aim of this study was to quantify the effects of N fertilization on fate of nitrogen and Chinese cabbage(Brassica chinensis L.) growth.Field plot and 15N microplot experiments were conducted to investigate N use efficiency(NUE),N fate and losses of chemical N fertilizers applied to an open field planted with Chinese cabbage.Total nitrogen loss, ammonia volatilization,denitrification loss and nitrous oxide emission were measured by labeled 15N technique,enclosure method,and acetylene inhibition-soil core incubation technique,respectively.Results showed that application of chemical N fertilizers significantly increased Chinese cabbage yield.NUE of the N fertilizers by difference method ranged from 25.3% to 47.2%,and the corresponding figure by trace method was in the range of 18.1%-24.6%.Application of chemical N fertilizer markedly increased gaseous nitrogen losses including ammonia volatilization(0.97%-17.1% of applied N),denitrification losses(4.33%-8.55% of applied N),and N2O emissions(1.09%-1.63% of applied N).At harvest 9.2%-10.9% of labeled urea was leached below 40 cm soil layer.Total N loss of urea ranged from 41.1% to 48.1% during Chinese cabbage growing season.It seems that apparent N leaching was the most important pathway of N losses,followed by ammonia volatilization,with denitrification being a minor pathway.Coated urea effectively reduced ammonia volatilization.