水稻机械化播栽对稻田甲烷和氧化亚氮排放的影响

Influence of rice mechanical planting methods on methane and nitrous oxide emissions from paddy field

为探明高产栽培条件下水稻机械化播栽对稻麦两熟农田稻季甲烷（CH4）和氧化亚氮（N2O）排放的影响,以超级稻南粳44为材料,于2011年和2012年在麦秸还田和不还田两种条件下对机械直播、机械栽插、常规手栽3种水稻播栽方式的稻田CH4和N2O排放量和水稻产量进行了比较研究.结果表明,稻季CH4和N2O排放主要集中在水稻生育前中期,移栽至有效分蘖临界叶龄期CH4累积排放量占稻季总排放量的76.49%~91.13%,有效分蘖临界叶龄期至拔节N2O累积排放量占稻季总排放量的 33.56%~49.41%.麦秸还田显著提高稻季 CH4总排放量（P〈0.05）、降低 N2O 总排放量（P〉0.05）,机械栽插的稻季CH4总排放量较常规手栽略减3.25%~9.50%（P〉0.05）,机械直播显著低于机械栽插和常规手栽（P〈0.05）：2011年,麦秸不还田条件下机械直播较机械栽插和常规手栽稻季CH4分别减排15.69%和18.43%,麦秸还田条件下分别减排14.54%和22.66%;2012年,麦秸不还田条件下机械直播较机械栽插和常规手栽稻季CH4分别减排26.63%和32.12%,麦秸还田条件下分别减排30.51%和36.75%.机械直播较常规手栽显著增加稻季N2O总排放量0.16~0.97 kg/hm2（P〈0.05）,机械栽插和常规手栽的差异不大（P〉0.05）.机械直播的产量水平显著低于常规手栽（P〈0.05）,减产 8.43%~10.79%,机械栽插较常规手栽产量降低 1.27%~3.49%（P〈0.05）.稻季的全球增温潜势主要由排放 CH4产生,麦秸还田显著提高全球增温潜势（P〈0.05）,机械直播的全球增温潜势显著小于机械栽插和常规手栽（P〈0.05）.麦秸还田条件下,2011年和2012年机械直播的“单位产量的全球增温潜势”较常规手栽分别减少12.02%和28.71%（P〈0.05）.上述研究表明,在长江下游稻麦两熟区采用机械直播有利于减少稻季CH4排放,麦秸还田条件下机械直播替代常规手栽能减少稻田排放CH4和N2O产生的综合温室效应.

Methane （CH4） and nitrous oxide （N20） are 2 important long-lived greenhouse gases （GHGs） that contribute to global warming. Paddy soils have been identified as a dominant source of atmospheric CH4 and N20. Little information is available on the impacts of rice mechanical planting methods on CH4 and N20 emissions and rice yield in high production rice-wheat double cropping system. A field experiment was conducted with super rice cultivar Nanjing 44 as materials during the rice growing season from 2011 to 2012 in Suzhou, Jiangsu Province. By using static chamber/gas chromatographic techniques, in this two-year field experiment CH4 and N20 emissions were simultaneously measured under 3 rice planting methods： mechanical direct-seeding （MD）, mechanical transplanting （MT） and artificial transplanting （AT）. Each planting treatment was combined with either wheat straw retention or wheat straw removal. The results indicated that all treatments exhibited comparable seasonality in CH4 fluxes, showing an increase at the beginning and a decline later on. High N20 emissions were triggered by the midseason drainage episode during the rice growing season in 2011 and 2012. CH4 accumulative emissions from transplantation to critical stage of effective tillering accounted for 76.49%-91.13% of the total emissions during the rice growing season. N20 accumulative emissions from critical stage of effective tillering to elongation stage represented 33.56%-49.41% of the seasonal N20 emissions. Compared with wheat straw removal, wheat straw retention significantly increased seasonal total CH4 emissions by 125.96%-138.31% in 2011 and by 108.63%-127.10% in 2012 （P〈0.05）, respectively, and reduced the seasonal total N20 emissions by 2.83 %- 12.50% in 2011 and by 3.39%- 18.19% in 2012 （P〉0.05）, respectively. The MT slightly decreased CH4 emissions during the rice growing season by 3.25%-9.50% compared to the AT （P〉0.05）, while both treatments were significantly higher than that from the MD （P〈0.05）. The seasonal total CH4 emissions in the MD were respectively 15.69% and 18.43% lower than those in the MT and AT with wheat straw removal, and 14.54% and 22.66% lower than those with wheat straw retention in 2011. And in 2012, the seasonal total CH4 emissions in the MD were correspondingly 26.63% and 32.12% lower than those in the MT and AT with wheat straw removal, and 30.51% and 36.75% lower than those with wheat straw retention, respectively. Compared with the AT, MD significantly increased N20 emissions during the rice growing season by 0.16-0.97 kg/hm2 in 2011 and 2012 （P〈0.05）. The seasonal total N20 emissions were comparable between the MT and the AT （P〉0.05）. For the years of 2011 and 2012, the rice yields under the AT were the highest, followed by the MT, and the yield under the MD was the lowest. Compared with the AT, the MD significantly decreased rice yield by 8.43%-10.79% （P〈0.05）, while the MT slightly decreased yield by 1.27%-3.49% （P〉0.05）. CH4 was more important in the 2 GHGs in that the effect of the seasonal CH4 emissions from rice-wheat double cropping system on climate was approximately 4 times greater than that of N20 emissions. The global warming potential （GWP） of CH4 and N20 emissions in the plots with wheat straw retention was 116.23%-130.35% higher than that in the plots with wheat straw removal in 2011 and 87.72%-118.04% in 2012 （P〈0.05）. The GWP in the MD was significantly lower than those in the MT and the AT （P〈0.05）. The GWP per yield in the MD was respectively 12.02% and 28.71% lower than that in the AT with wheat straw retention in 2011 and 2012 （P〈0.05）. The overall results indicated that the MD could effectively decrease total CH4 emissions during the rice growing season; with wheat straw retention, the conversion from AT to MD would reduce the comprehensive greenhouse effect resulting from the CH4 and N20 emissions in high production rice-wheat double cropping system in the downstream of the Yangtze River in China.