Resource And Environmental Costs Of Cropping Structure Change In China

As the core and foundation of Chinese agricultural structural adjustment,cropping structure is undergoing a transition from "Taking grain as the key link" to "Coordinated Grain and cash crop",at the same time,it is also accompanied by the continuous deterioration of the agricultural ecological environment.In order to fully understand the contribution of the cropping structure change on the cost of resource and environment and to provide a theoretical support for agricultural structure adjustment and sustainable development of agriculture in the future.this study estimated the material input rate of 16 major cropping systems.Combined with the carbon footprint model and cropland soil acidification model,this study also quantified the contribution of cropping structure change on the changes in fertilizer consumption,greenhouse gas emission,and cropland soil acidification in China.Then used multi-objective cropping structure optimization model to optimize the cropping structure in China by 2020.The main results of this study are as follows:1.Total fertilizer consumption in Chinese cropping system increased from 0.1 Mt(Million ton)in 1950 to 49.6 Mt in 2000,and 74.6%of the increase was attributed to FAR,0.1%to TCA,and 25.3%to CS.The contribution of FAR to total fertilizer consumption decreased(from 98.3%in the 1950s to 65.6%in the 2000s),while the contributions of TCA and CS increased(from 0.9 and 0.8%in the 1950s to 17.5 and 16.8%in the 2000s,respectively).Maize,rice,and wheat were the major crops to which most of the fertilizers(up to 87.9%)were applied before the 1980s.However,maize,vegetables and fruits became the major drivers of fertilizers consumption after the 1980s,which contributed to 90.6%of incrased consumption of fertilizer in the 2000s.2.Carbon emission and sequestration in Chinese cropping systems increased by 329.3 and 136.1 Mt CO2 from 2001 to 2014,the increase was attributed to TCA,carbon emissions rate or carbon sequestration(CER and CSR)and CS changes.Total net carbon emission increased from 288.7 Mt CO2 in 2001 to 490.4 Mt in 2014,and 15.9%of the increase was attributed to TCA change,95.4%to net carbon emission rate(NCER)change,and-11.3%to CS change.Rice,wheat,maize,vegetables and fruits were the major carbon emission or carbon sequestration production systems.The increase in carbon emission or sequestration was mainly because of the increase in CER or CSR of wheat,maize,vegetables and fruits,and the increase in CS of maize,vegetables and fruits.3.Total H+ production in Chinese cropland soil increased by 328.5 Mkeq from 2001 to 2014.And 32.9%of the increase was attributed to TCA change,59.2%to H+ production rate(H+per)change,and 7.9%to CS change,while the contribution of H+per change to the increase in total soil H+ in cropland decreased.The increase in soil acidification from 2001 to 2014 was mainly due to the increase in H+per of vegetables,fruits,oilseed rape and cotton(contribution of the total H+ production increase are 32.6%,21.6%,12.9%and 11.4%respectively),and the increase in CS of vegetables,fruits and maize(contribution of the total H+ production increase are 6.4%9.9%and 10.4%respectively).4.The optimized cropping systems in 2020 will require 51.5 Mt of chemical fertilizer,348.5 Mt CO2 of net carbon emission and 1159.8 Mkeq of H+ production in cropland soil and 13464.3 billion CNY of net profit.Compared with 2014,this optimized cropping system can reduce 2.2 Mt chemical fertilizer input,CO2 emission by 82.1 Mt and cropland soil H+ production by 140.7 Mkeq,and increase the net profit of 5.8 billion CNY,at the same time reducing the area of cultivated land by 10481.7 thousand hectares without considering the double cropping.In summary,the cropping structure change can potentially affect the consumption of chemical fertilizers,greenhouse gas emission and soil acidification in cropping systems.Future research should strengthen the application of Integrated Soil-crop System Management(ISSM)to the key crop system,such as maize,vegetables and fruits.In addition,reducing the use of chemical nitrogen fertilizer and high-concentration phosphate fertilizer,increasing fertilizer use efficiency and manure application,raising the rate of straw return,and optimizing the adjustment of cropping structure will be the most direct,effective and economic way to realize agricultural sustainable development and alleviate greenhouse gas emission and cropland soil acidification in China.