Fertilizer nitrogen loss via N2 emission from calcareous soil following basal urea application of winter wheat

摘要

TThe ratio of nitrous oxide (N_(2)O) to N_(2)O plus nitrogen gas (N_(2)) emitted from soils (N_(2)O/(N_(2)O+N_(2))) is regarded as a key parameter for estimating fertilizer nitrogen (N) loss via N_(2) emission at local, regional or global scales. However, reliable measurement of soil N_(2) emissions is still difficult in fertilized soil-crop systems. In this study, the N loss via N_(2) emission following basal urea application (with a dose of 150 kg N ha~(?1)) to a calcareous soil cultivated with winter wheat was quantified using the helium-based gas-flow-soil-core technique. Emissions of N_(2) and N_(2)O from sampled fresh soils were measured under simulated field soil temperature and oxygen conditions. Our observation performed on the first day after irrigation and rainfall events showed the highest N_(2) and N_(2)O emissions, which amounted to approximately 11.8 and 3.8 μg N h~(?1) kg~(?1) dry soil, corresponding to 3304 and 1064 μg N m~(?2)?h~(?1), respectively. The N_(2)O/(N_(2)O+N_(2)) molar ratios within about 10?days following fertilization ranged from 0.07 to 0.25, which were much larger than those at the other time. During the one-month experimental period, the urea-N loss via emissions of N_(2), N_(2)O, and N_(2)+N_(2)O was 1.6%, 0.6%, and 2.2%, respectively. Our study confirms that the widely applied acetylene-inhibition method substantially underestimates fertilizer N losses via N_(2) emissions from calcareous soils cultivated with winter wheat.摘要准确定量施肥农田土壤的N_(2)排放仍然困难。本研究基于华北冬小麦季的一次基肥（尿素150 kg N ha~(–1)）施用事件，采用氦培养-直接测定N_(2)法，在与田间土壤温度和氧气含量一致的条件下测定鲜土的N_(2)和N_(2)O排放。结果显示：施肥和灌溉/降雨事件共同促进N_(2)和N_(2)O出现峰值排放；施肥导致N_(2)O/(N_(2)O+N_(2))摩尔比增加至0.25；基肥施用后的一个月内，土壤N_(2)和N_(2)+N_(2)O排放损失分别占肥料氮投入的1.6%和2.2%。我们的结果证实了广泛采用的乙炔抑制法极大的低估了冬小麦田石灰性土壤N_(2)排放造成的肥料氮素损失。