露地种植大白菜的氮肥效应与氮素损失研究

采用田间小区和微区试验,研究了施用化学氮肥在露地大白菜上的氮肥效应和氮素损失。氮素总损失用15N示踪法测定,氨挥发用通气密闭室法测定,反硝化损失用乙炔抑制原状土柱培养法测定,不加乙炔测定N2O排放。结果表明,施用化学氮肥增产显著,用差值法计算得到的氮肥利用率在25.3%4～7.2%之间,相应的示踪法氮肥利用率为18.1%2～4.6%。化学氮肥显著增加了氨挥发、反硝化和N2O排放等气态氮损失;其中氨挥发占施氮量的0.97%1～7.1%,反硝化占4.33%8～.55%,N2O排放在1.09%1～.63%之间变化。大白菜收获时9.2%～10.9%的标记尿素被淋洗到40.cm以下土层。试验期间尿素的氮素总损失达41.1%4～8.1%,以表观淋洗损失最为严重,其次是氨挥发,而反硝化损失最低。与普通尿素相比,包衣尿素明显降低了氨挥发。

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.