中国秸秆资源的时空分布、利用现状与碳减排潜力

Temporal and Spatial Distribution,Utilization Status,and Carbon Emission Reduction Potential of Straw Resources in China

为了解中国农作物秸秆资源量近40年的变化趋势及当前的空间分布特征和主要利用方式,估算秸秆利用碳减排潜力,采用草谷比法对1981~2020年间全国农作物秸秆资源量进行了科学估算,分析了秸秆资源密度和人均资源量的时空分布特征,并估算了秸秆制备生物炭基肥的碳减排潜力.结果表明:(1) 1981~2020年我国农作物秸秆总量增长了4.39×10~8 t,且总体呈不断增长的趋势.(2) 2020年全国作物秸秆理论资源总量约7.72×10~8 t;水稻、小麦和玉米秸秆仍旧是主要的农作物秸秆种类,约占秸秆资源总量的84%.东北和华北地区秸秆资源量最丰富,东北地区人均资源占有量最高,约1.46 t;华北地区秸秆资源密度最高,达5.42 t·hm^(-2).(3)我国农作物秸秆综合利用率逐年提高,目前主要以肥料化和饲料化利用方式为主,约占所有秸秆利用方式的77.5%.(4) 2020年我国可收集农作物秸秆资源可制备成生物炭2.04×10~8 t,制备生物炭过程中可更新能源代替化石燃料可减少二氧化碳当量(CO_(2e))排放1.45×10~8 t,生物炭封存CO_(2e)约4.63×10~8 t,施用生物炭可减少化肥施用实现CO_(2e)减排8.58×10~5 t,施用生物炭促进农作物增产可减排CO_(2e)约7.77×10~6 t,生物炭对N_(2)O的释放抑制可减少CO_(2e)排放3.84×10~6 t,原料、生物炭运输和生物炭散播过程中温室气体排放量为3.32×10~7 t,最终温室效应缓解净潜力的减排CO_(2e)为5.86×10~8 t.农作物秸秆制备成生物炭具有较大的潜力,同时也是实现碳减排的有效途径.

Based on the crop yield data of China and each region from 1981 to 2020(excluding data from Hong Kong,Macao,and Taiwan),by using the grain-straw ratio method,this study estimated the total amount of crop straw and collectable amount of crops,including corn,rice,wheat,other cereals,cotton,rapeseeds,peanuts,beans,tubers,sesame,fiber crops,sugarcane,and beetroots,and the spatial and temporal distribution characteristics of resource density and per capita resources of crop straw were analyzed.This study analyzed the current utilization mode,development,and change of crop straw in China.Finally,we used the life circle assessment(LCA) method to estimate the carbon emission reduction potential of biochar prepared from crop straw.The main findings were:from 1981 to 2020,the temporal distribution trend of theoretical crop straw resources and collectable straw resources in China generally showed a steady growth trend,and the two increased from 3.33×10~8 t and 3.04×10~8 t in 1981 to the highest values of 7.70×10~8 t and 6.63×10~8 t in 2020,with a net increase of 4.37×10~8 t and 3.59×10~8 t,respectively.The net increase in rice,wheat,and corn straw resources was 3.69×10~8t,accounting for between 77% and 85% of the total crop straw and always occupying the main position of straw resources in China.The proportion of wheat straw in the total amount of straw was maintained at approximately 20%,rice straw resources decreased from 44% to 28.4%,and corn straw increased from 19.9% to 34.2% from 1981 to 2020.In 2020,the total theoretical resources of crop straw in China were 7.72×10~8 t,and the source structures were:rice 28.4%,wheat 21.45%,corn 31.45%,other cereals 1.4%,beans 3.4%,tubers 0.82%,cotton 2.28%,peanuts 2.97%,rapeseeds 3.4%,sesame 0.12%,fiber crops 0.06%,beetroots 0.67%,and sugarcane 0.84%.As to the spatial distribution of crop straw resources in China in 2020,the locations with straw resources ≥60 million tons included Heilongjiang,Henan,and Shandong,of which Henan had as much as 88.56 million tons;those with between 40 million and 60 million tons included Hebei,Inner Mongolia,Jiangsu,and Anhui;those with between 20 million and 40 million tons included Liaoning,Jilin,Jiangxi,Hubei,Hunan,Sichuan,Yunnan,and Xinjiang;and the straw resources in the rest of the region were below 20 million tons.Rice straw was mostly distributed in the middle and lower reaches of the Yangtze River and the Northeast region,of which the amount of Heilongjiang rice straw was the largest,with 31.86 million tons;wheat straw was mainly distributed in North China,with Henan having the most abundant resources(48.04 million tons).Corn straw was mainly distributed in Northeast China and North China,of which Heilongjiang and Inner Mongolia corn straw resources were relatively rich,with 33.18 million tons and 29.90 million tons,respectively.Crop straw resource density and per capita resources were shared in 2020 in China.The average density of crop straw resources in China was 4.61 t·hm^(-2),and the average densities of crop straw resources in various agricultural areas were 5.39 t·hm^(-2) in Northeast China,5.42 t·hm^(-2) in North China,4.45 t·hm^(-2) in the Mengxin Region,4.44 t·hm^(-2) in the middle and lower reaches of the Yangtze River,3.92 t·hm^(-2)in Tibet,3.40 t·hm^(-2) in the Loess Plateau,3.08 t·hm^(-2) in South China,and 2.91 t·hm^(-2) in Southwest China.The average per capita share of straw resources was 0.55 t.The average values of per capita straw resources in each region were:1.46 t in the Northeast area,1.20 t in the Mengxin Region,0.47 t in North China,0.44 t in the middle and lower reaches of the Yangtze River,0.40 t in the Loess Plateau,0.37 t in the Southwest area,0.33 t in the Qinghai-Tibet area,and 0.20 t in the South China area.The utilization of crop straw in China was diversified.Fertilizer and feed were the main utilizations,accounting for 62.1% and 15.4%,respectively.In 2020,collectable crop straw resources for the preparation of biochar totaled 2.04×10~8 t in China.Renewable energy replaced fossil fuels in the process of preparing biochar,which could reduce CO_(2e)(CO_(2e):CO_(2) equivalent) emissions by 1.45×10~8 t.Biochar could sequester approximately 4.63×10~8 t of CO_(2e);biochar application was able to reduce chemical fertilizer application to achieve a CO_(2) emission reduction of 8.58×10~5 t;and biochar application could promote crop yield in order to reduce CO_(2e) emissions by approximately 7.77×10~6 t.The inhibition of N_(2)O release by biochar was able to reduce CO_(2e) emissions by 3.84×10~6 t.Greenhouse gas emissions from raw materials,biochar transportation,and biochar dispersion were reduced by 3.32×10~7 t,and the net potential for final greenhouse effect mitigation was 5.86×10~8 t for CO_(2e) reduction.The total potential of crop straw in China to reduce the greenhouse effect was 6.2×10~8 t,of which biochar in soil storage and coal substitution accounted for 74.6% and 23.4%,respectively.In the process of biochar preparation and application,the total greenhouse gas emission was 3.32×10~7 t,and the net greenhouse effect emission reduction reached 5.86×10~8 t,i.e.,it could sequester 0.88 t CO_(2e) per ton of raw materials.The net greenhouse gas emission reduction of unused straw was 6.73×10~7 t in 2020.With the continuous harvest of grain crops in China,the potential of biochar preparation and carbon sequestration will increase yearly.Using crop straw to prepare biochar has great potential and will be one of the most effective ways to achieve carbon emission reduction in agriculture.It is suggested that government departments should pay attention to the preparation of biochar,support the field experiments of biochar application effects after applying soil on policy and funds,and then introduce relevant biochar standards to ensure the scientific application of biochar prepared by crop straw according to local conditions,so as to achieve the dual benefits of carbon emission reduction and soil remediation and yield increase.