稻麦轮作系统冬小麦农田耕作措施对氧化亚氮排放的影响

2008—2011年,采用静态箱-气相色谱法对长江下游稻麦轮作系统冬小麦农田N2O排放进行了为期3a的田间原位观测,研究不同耕作措施(免耕、旋耕和翻耕)对冬小麦生长季N2O排放的影响。结果表明:不同耕作措施下冬小麦农田N2O排放高峰出现在施用基肥后的1个月内以及施用孕穗肥后的4月中旬至小麦成熟期,其余时间N2O排放通量均较小。年度和耕作措施对冬小麦农田N2O季节排放总量均有极显著影响(P<0.01),不同处理N2O季节排放总量表现为免耕>翻耕>旋耕,2008—2011年3年平均分别为2.50 kg/hm2、2.05 kg/hm2和1.66 kg/hm2,免耕比翻耕增加N2O排放22.0%(P<0.05),旋耕比翻耕减排19.0%(P<0.05)。冬小麦生长期内施用孕穗肥后1个月内N2O排放通量与农田土壤充水孔隙率(WFPS)及10 cm地温呈显著(P<0.05)或极显著(P<0.01)正相关,2009—2010年施用基肥后1个月内N2O排放通量与WFPS呈显著负相关(P<0.05)。结果说明旋耕是减少长江下游稻麦轮作系统冬小麦农田N2O排放的最佳耕作措施。

Nitrous oxide emissions affected by tillage measures in winter wheat under a rice-wheat rotation system

It is well documented that nitrous oxide (N₂O) emissions from agricultural soils are the result of complex interactions between climatic parameters and the physical, chemical, and biological properties of soils. Adopting no tillage or reduced tillage may therefore potentially affect N₂O emissions from croplands through effects on soil properties; however, net effects are inconsistent and not well quantified globally. We used static chamber and gas chromatography techniques to examine the effects of different tillage measures (no tillage, rotary tillage, plow tillage) on N₂O emission fluxes during the winter wheat season over 3 years (2008-2011) under a rice-wheat rotation system, in the lower reaches of the Yangtze River. The characteristic seasonal variation in N₂O emissions during the winter wheat season under different tillage measures was defined as the peak in N₂O flux observed within one month of basic fertilizer application, and/or from mid-April to the maturity stage of wheat after booting fertilizer application. Total N₂O emissions were significantly influenced by year and tillage measures (P<0.01). Total N₂O emissions were: no tillage > plow tillage > rotary tillage, averaging 2.50, 2.05 and 1.66 kg/hm², respectively. Total N₂O emissions for no tillage were 22.0% higher than for plow tillage (P<0.05), and rotary tillage was 19.0% lower than plow tillage (P<0.05). Correlation analysis showed that the relationship between N₂O emission flux, soil water-filled pore space (WFPS), and soil temperature at 10 cm depth within a month of fertilization, varied with year and fertilization time. In 2009-2010, there was a significantly negative correlation between the N₂O emissions flux and WFPS within a month of basic fertilizer application (P<0.05). In 2008-2011, significantly positive correlations between the N₂O emissions flux and WFPS, and soil temperature at 10 cm depth within the month after booting fertilizer application were also found (P<0.05 or P<0.01). This illustrated that rotary tillage can effectively decrease total N₂O emissions during the winter wheat season in a rice-wheat rotation system; this is thus the best tillage measure to reduce the greenhouse effect in the lower reaches of the Yangtze River.