施肥方式对冬小麦—夏玉米轮作土壤N_2O排放的影响

氧化亚氮(N_2O)是一种重要的农田温室气体,本研究利用紫色土长期施肥试验平台,采用静态箱/气相色谱法对紫色土旱作农田冬小麦—夏玉米轮作系统的N_2O排放进行了定位观测(2012年11月至2013年9月),研究单施氮肥(N)、常规氮磷钾肥(NPK)、猪厩肥(OM)、猪厩肥配施氮磷钾肥(OMNPK)和秸秆还田配施氮磷钾肥(ICRNPK)等施肥方式对紫色土N_2O排放特征的影响;不施肥(NF)作为对照计算排放系数,以探寻紫色土地区可操作性强、环境友好的施肥方式。结果表明,所有施肥方式的N_2O排放均呈现双峰排放,峰值出现在施肥初期;玉米季N_2O排放峰值显著高于小麦季(p0.05)。在相同的施氮水平(小麦季130 kg hm~(~(-2)),玉米季150 kg hm~(~(-2)))下,施肥方式对N_2O排放和作物产量均有显著影响(p0.05)。N、OM、NPK、OMNPK和ICRNPK处理的土壤N_2O周年累积排放量分别为1.93、1.96、1.12、1.50和0.79 kg hm~(~(-2)),排放系数分别为0.62%、0.63%、0.33%、0.47%和0.21%,全年作物产量分别为4.35、11.95、8.39、9.77、10.93 t hm~(~(-2))。施用猪厩肥显著增加N_2O排放量,而秸秆还田在保证作物产量的同时显著降低N_2O排放量,可作为紫色土地区环境友好的施肥方式。土壤无机氮(NO_3~--N和NH_4~+-N)是N_2O排放的主要限制因子。因此,在施氮水平相同时,施肥方式对紫色土活性氮含量的影响导致N_2O排放差异显著,是土壤N_2O排放差异的根本原因。土壤孔隙充水率也是影响N_2O排放的重要环境因子,并且其对N_2O排放的影响存在阈值效应。

Effect of Fertilization Regime on Soil N2O Emission from Upland Field under Wheat-Maize Rotation System

Agricultural soils have been determined to contribute at present about 60% to the global anthropogenic nitrous oxide (N₂O) emission due to N fertilization. It is a great challenge to guarantee high crop yields while reducing N₂O emissions under continuous application of nitrogen fertilizers. However, few field data sets are available for exploration of effects of fertilizer N regimes on soil N₂O emission in the Sichuan Basin, one of the regions the most intensive in agriculture in China. The main objectives of this research were to screen out optimal N fertilizer management practices which would not only reduce soil N₂O emission, but also maintain high crop yields. Static chamber-gas chromatographic techniques had been used to measure soil N₂O emissions from the purple soil under long-term N fertilization of pure synthetic N fertilizer (N), synthetic NPK fertilizer (NPK), pig manure (OM), pig manure plus synthetic NPK fertilizer (OMNPK) and incorporation of crop residues plus synthetic NPK fertilizer (ICRNPK). A plot with no fertilizer (NF) applied was set as control for emission coefficient calculation. In-situ field measurements were conducted through the wheat-maize rotation season from November 2012 to September 2013. N₂O emission showed a double-peak curve during the season regardless of fertilization regime. The peaks occurred in the first days after fertilization. However, the peak in the maize season was significantly higher than that in the wheat season (p < 0.05). Fertilization regimes influenced cumulative N₂O fluxes and grain yields significantly (p < 0.05). When the total N application rate was the same for all the treatments, 130 kg hm^-2 in the wheat and 150 kg hm^-2 in the maize season, Treatment N, OM, NPK, OMNPK and ICRNPK was 1.93, 1.96, 1.12, 1.50 and 0.79 kg hm^-2, respectively, in cumulative N2O flux, 0.62%, 0.63%, 0.33%, 0.47% and 0.21%, respectively, in emission coefficient, and 4.35, 11.95, 8.39, 9.77, 10.93 t hm^-2, respectively, in total annual grain yield. In comparison with Treatment NPK, Treatment OM enhanced N₂O emission significantly, whereas, Treatment ICRNPK significantly reduced N₂O emission and maintained high crop yields, as well. Therefore, incorporation of crop residues plus synthetic fertilization (ICRNPK) is recommended as an optimal fertilization regime in croplands of purple soil. Content of inorganic N (ammonium and nitrate) was the main controlling factor of soil N₂O emission. Therefore, the difference in N₂O emission flux was attributed to variation of the content of inorganic N induced by fertilization regime. That was also the reason why the fertilization regime, Treatment as ICRNPK, could effectively reduce N₂O emission. Soil water filled pore space (WFPS) might be another important factor affecting soil N₂O emission with a threshold effect. Therefore, it can be concluded that N₂O emissions from upland croplands under the wheat-maize rotation system can be reduced by optimizing timing and rate of N application in the light of crop growth and antecedent soil WFPS.