Contributions of agricultural plants and soils to N₂O emission in a farmland

Abstract. The goal of this study was to quantify the roles of plants and soil in the N₂O budget of a cropland in North China. Plant and soil N₂O fluxes were measured with transparent and dark plant chambers and soil chambers, respectively, in three adjacent fields of fertilized cotton, fertilized maize and unfertilized soybean. During the observation period, the soil flux was 448 ± 89, 230 ± 74 and 90 ± 14 μg N₂O m⁻² h⁻¹ in cotton, maize and soybean fields, respectively. The plant flux was 54 ± 43 and 16 ± 41 μg N₂O m⁻² h⁻¹, about 10 % and 26 % to the total ecosystem flux, for the cotton and the soybean field, respectively. Ignoring the contribution of plants would cause an obvious underestimation on the ecosystem N₂O flux. The influence of sunlight on plant N₂O flux was insignificant. However, in the cotton field, the responses of the plant N₂O flux to air temperature and soil ammonium content were significant under sunlight but insignificant under darkness, suggesting that stomatal activity might influence the release process. In the cotton field, temperature sensitivity of plant N₂O emission was 1.13, much lower than the value of soil flux (5.74). No relationship was found between plant N₂O flux and soil nitrate content. It was implied that nitrate reduction in plants might not be the main source of plant N₂O emission under field conditions. The seasonal patterns of the soil and plant N₂O emissions were similarly affected by fertilization, indicating that plants might serve as a passive conduit transporting N₂O produced in the soil.