关键词:气候变化;碳排放;水稻;生命周期评价法;中国 Abstract Global warming has raised public concern and reducing anthropogenic carbon emissions has become a heated issue. Agriculture plays an important role in greenhouse gas (GHG)emission and offsetting. Rice is one of China’s three major cereal crops and assessing the carbon footprint (CF)of rice production is a vital component of low-carbon goal in China’s agriculture. Data from China Agricultural Statistics from 2004 to 2014 were collected for estimating CF and its components in rice production. The results showed that GHG emissions and CF per area were observed an annual average increase rate of 2.12 billionkgCO2-eq,32.58kgCO2-eq/ha respectively,and annual reduction of CF per yield is -2.82kgCO2-eq/t. Results varied among provinces. For example,the average CF per unit area of rice was the highest in Jiangsu at 7411.91kgCO2-eq/ha and the least in Heilongjiang province at 4305.87kgCO2-eq/ha;average CF per unit of production was highest in Hainan at 2.36 times higher than Jilin Province (the lowest one). In the double cropping rice area of southern China(Guangxi,Guangdong and Fujian)and the double cropping rice area of central China (Jiangsu,Hunan and Jiangxi),the carbon footprints are higher than the national average. CH4 emissions were the largest component of CF,accounting for 85.05% of the total carbon emission following by agricultural inputs for 14.95%,and fertilizer inputs for 10.25% of the agricultural inputs. Strategies to reduce GHGs emissions and improve carbon efficiency in rice production depends on a combination of field operations such as intermittent irrigation,suitable usage of fertilization and other agricultural inputs,and improved mechanical efficiency.
本研究结合生命周期评价法(LCA)和ISO/TS14067[28]产品碳足迹核算方法对中国水稻生产碳足迹进行研究。根据数据的可获得性和连续性,选取2004-2014年为研究年限,研究的系统边界为水稻从播种到收获全过程各项投入造成的温室气体排放,具体包括各项农资(化肥、种子、农膜、柴油、灌溉耗电、农药等)投入温室气体排放,水稻生育期内稻田CH4排放等。碳足迹计算方法及稻田CH4排放的相关参数均来源于《2006年IPCC国家温室气体清单指南》[29]。水稻从播种到收获过程的农资投入碳足迹计算为: (1) 式中AIi为第i种投入;EFi为第i种投入的排放参数(见表1);n为水稻生产过程消耗的n种能源(柴油和电能等)或生产资料(化肥、农药和种子等)。本研究统一使用CO2排放当量(kgCO2-eq)作为温室气体排放量的核算单位。 Table 1 表1 表1水稻生产排放清单及转换因子 Table 1List of emissions and conversion factors in agricultural inputs of rice production
2004-2014年中国水稻生产的温室气体排放量呈现不断增长的趋势(图1a)。2004年水稻生产温室气体排放总量约为1614.15亿kgCO2-eq,到2014年达到1811.48亿kgCO2-eq,年均增长量约为21.24亿kgCO2-eq(R2=0.9218,P<0.0001)。2006年出现最低值,为1595.55亿kgCO2-eq,2014年出现最大值。在水稻生产单位面积碳足迹方面(图1b),2004年水稻生产单位面积碳足迹为5788.41kgCO2-eq/hm2,到2014年达到6072.00kgCO2-eq/hm2,年均增长量为32.58kgCO2-eq/hm2(R2=0.6617,P=0.0023),水稻生产单位面积碳足迹与温室气体排放总量年际趋势表现一致,增长明显;水稻生产单位产量碳足迹呈明显年际波动,总体下降的趋势(图1c),2004年水稻生产单位产量碳足迹为918.75kgCO2-eq/t,到2014年降至893.74kgCO2-eq/t,年均增长量为-2.82kgCO2-eq/t(R2=0.3340,P=0.0626)。 显示原图|下载原图ZIP|生成PPT 图12004-2014年中国水稻生产温室气体排放量及单位面积、单位产量碳足迹年际变化 -->Figure 1Total greenhouse gas emissions,carbon footprint per area and carbon footprint per yield of rice production in China from 2004 to 2014 -->
3.2 各省水稻生产碳足迹
(1)水稻生产碳足迹分析。本研究对2004-2014年中国主要省份水稻生产碳足迹进行了计算分析(图2)。从全国总体来看,水稻生产的单位面积排放与单位产量排放存在显著正相关关系(R2=0.4845,P<0.001)。另一方面,综合比较不同省份单位面积、产量碳足迹发现:华南双季稻稻作区(广西、广东、福建等),华中双季稻稻作区(江苏、湖南、浙江等)大部单位面积碳足迹,单位产量碳足迹均大于全国平均水平。而西南稻作区(四川、重庆、贵州等),华北单季稻稻作区(河南、河北、山东),东北早熟单季稻稻作区(黑龙江、吉林、辽宁)均小于全国水平。双季稻产区的温室气体排放压力明显。 显示原图|下载原图ZIP|生成PPT 图22004-2014年中国部分省(市、自治区)水稻年均单位产量及年均单位面积碳足迹分布 -->Figure 2Average annual carbon footprint per yield and per area in provincial rice production of research area in China from 2004 to 2014 -->
(2)水稻生产温室气体排放。图3a所示,水稻生产温室气体排放主要集中在中国华南、华中双季稻稻作区(湖南、湖北、江西等),是中国传统的水稻种植区;其次随着东北地区水稻种植业的发展,以黑龙江为代表的东北早熟单季稻稻作区温室气体排放增加快速。而水稻生产温室气体排放总量较小的华北各省(河北、山东、河南等),其单位产量碳足迹普遍较大。在各省水稻温室气体排放总量中,湖南水稻生产温室气体排放总量最大,年均为234.32亿kgCO2-eq,其次为江西(187.85亿kgCO2-eq)和江苏(165.19亿kgCO2-eq);河北年均最小(4.19亿kgCO2-eq),其次为山东(6.46亿kgCO2-eq)和海南(20.08亿kgCO2-eq)。省际间水稻种植温室气体排放量存在明显差距,其中湖南水稻生产温室气体排放量是河北的55.79倍。 显示原图|下载原图ZIP|生成PPT 图32004-2014年中国部分省(市、自治区)水稻温室气体排放及单位面积、单位产量碳足迹年均增长量分布 -->Figure 3Average annual increases in greenhouse gas emissions,carbon footprint per area or yield in some provincial rice in China from 2004 to 2014 -->
根据2004-2014年的计算结果,中国水稻生产碳足迹组成中水稻种植产生的CH4占比最大,约占总碳足迹的85.05%,农资投入品引起的碳足迹占14.95%(图4)。在农资投入品中,占比最大的为化肥投入,占总碳足迹的10.25%,种子、地膜、柴油以及农药投入造成的碳足迹只占总碳足迹的4.70%,稻田CH4排放是水稻生产过程中主要的温室气体排放来源。各个省份水稻生产碳足迹组分占比虽然有一定程度的差别,但是总体结构与上述分析一致。在农资投入排放方面,水稻生产所用农资投入引起的温室气体排放量年均增长约8.65亿kgCO2-eq,而稻田CH4引起的温室气体排放年均增长量约为12.5亿kgCO2-eq。随着中国水稻种植面积、产量的增长以及农业现代化的发展,水稻生产引起的温室气体排放对环境的影响有不断加剧的趋势。 显示原图|下载原图ZIP|生成PPT 图42004-2014年中国水稻生产碳足迹结构组分占比 -->Figure 4Components of carbon footprint in China’s rice production from 2004 to 2014 -->
(1)2014年中国水稻生产温室气体排放量、单位面积碳足迹、单位产量碳足迹分别为1811.48亿kgCO2-eq、6072.00kgCO2-eq/hm2和893.74kgCO2-eq/t,2004-2014年间年均增长量分别达21.24亿kgCO2-eq、32.58kgCO2-eq/hm2和-2.82kgCO2-eq/t。 (2)2004-2014年各省水稻生产温室气体排放量,单位面积碳足迹,单位产量碳足迹差异明显。综合比较单位面积与单位产量碳足迹发现,华南双季稻稻作区(广西、广东、福建等)、华中双季稻稻作区(江苏、湖南、浙江等)的大部单位面积碳足迹,单位产量碳足迹均大于全国平均水平;西南稻作区(四川、重庆、贵州等),华北单季稻稻作区(河南、河北、山东),东北早熟单季稻稻作区(黑龙江、吉林、辽宁)大部单位面积碳足迹,单位产量碳足迹均小于全国水平。双季稻产区的温室气体排放压力明显。 (3)2004-2014年间水稻生产碳足迹各组分占比变化幅度不大,其中平均占比最大的部分为稻田CH4排放,为85.05%。农资投入引发的温室气体排放仅占14.95%,其中化肥投入占总碳足迹的10.25%。 中国水稻生产温室气体排放压力呈逐步增长的状态,合理调整中国水稻生产布局,优化稻田管理措施,推广水稻高效种植模式,提高农资综合利用效率是缓解中国水稻温室气体排放压力的关键。 The authors have declared that no competing interests exist.
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