Responses of N2O and CH4 fluxes to fertilizer nitrogen addition rates in an irrigated wheat-maize cropping system in northern China

[摘要] Model and field studies generally posit that when the application rates ofnitrogen fertilizer exceed crop needs, nitrous oxide (N₂O) emissionswill increase nonlinearly, though linear responses are also extensivelyreported by field studies. We conducted year-round measurements of cropyield, N₂O and methane (CH₄) fluxes for treatments of sixfertilizer nitrogen levels (0, 135, 270, 430, 650 and 850 kg N ha⁻¹ yr⁻¹ in the form of urea) in a typical irrigated wheat-maize rotationfield in northern China. Linear models characterized the responses ofcumulative N₂O emissions to fertilizer rates well; therefore, thecalculated N₂O emission factors of 0.17 ± 0.02%, 0.73 ± 0.05% and 0.49 ± 0.02% for the wheat season, maizeseason and annual scale, respectively, were appropriate for the differentfertilizer rates. The cumulative CH₄ uptake by the soil tended to beenhanced at higher fertilizer rates (≥350 kg N ha⁻¹) in the maizeseason whereas no effect was observed for the wheat season. When the annualfertilizer rates increased from 270 to 430, from 270 to 650, and from 270 to850 kg N ha⁻¹ yr⁻¹, the crop yields increased only 3 ∼ 15%(0.5 ∼ 2.1 t ha⁻¹ yr⁻¹), but cumulative N₂O emissionsincreased 35 ∼ 115% (0.9 ∼ 3.0 kg N ha⁻¹ yr⁻¹). Werecommend 270 kg N ha⁻¹ yr⁻¹ as the locally optimum fertilizerrate. Considering the nitrogen inputs by fertilization (270 kg N ha⁻¹ yr⁻¹), irrigation (4.3 ± 0.2 kg N ha⁻¹ yr⁻¹) anddeposition (wet deposition: 30.5 ± 1.5 kg N ha⁻¹ yr⁻¹), theslightly positive soil nitrogen balance could maintain the current cropyield (∼13.8 t ha⁻¹ yr⁻¹) and reduce the present highN₂O emissions (>3.51 kg N ha⁻¹ yr⁻¹) of the local farmers'practice (fertilizer rate > 430 kg N ha⁻¹ yr⁻¹).

[学科分类] 地球化学与岩石