Nitrous oxide emission from upland crops and crop-soil systems in northeastern China

Although it is known that crops can directly emit N2O, their contribution to the total N2O emission from crop-soil systems under field conditions is not well understood. This study was conducted to study the contribution of crops to total N2O emission from soybean-soil and maize-soil systems in northeastern China. The effects of N fertilization on N2O emission and NO3−-N concentration in plants were also studied. The emission from crop-soil systems was measured with the closed chamber method, whereas the direct emission from crops was measured with the soil surface-sealed method. The addition of fertilizer N significantly increased the NO3−-N concentration in crops and enhanced the N2O emission from crop-soil systems and from crops alone. The amount of N2O emitted directly from soybean plants accounted for 6 to 11% of the total soybean-soil emission. Similarly, the amount of N2O emitted directly from maize plants accounted for 8.5 to 16% of the total maize-soil emission. The proportion of the applied N lost through direct N2O emission from plants ranged from 0.19 to 0.34%, whereas the proportion of the applied N lost through N2O emission from the crop-soil system ranged from 1.1 to1.9%. These results suggest that the use of chambers that do not include plants may lead to an underestimation of the total N2O emission from crop-soil systems.