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

Abstract

The ratio of nitrous oxide (N2O) to N2O plus nitrogen gas (N2) emitted from soils (N2O/(N2O+N2)) is regarded as a key parameter for estimating fertilizer nitrogen (N) loss via N2 emission at local, regional or global scales. However, reliable measurement of soil N2 emissions is still difficult in fertilized soil-crop systems. In this study, the N loss via N2 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 N2 and N2O 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 N2 and N2O 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 N2O/(N2O+N2) 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 N2, N2O, and N2+N2O 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 N2 emissions from calcareous soils cultivated with winter wheat.

Keywords

• denitrification
• fertilizer nitrogen loss
• n2 emission
• n2o/(n2o+n2)
• calcareous soil