| Agricultural production is seriously influenced by the change of climate,and it also reacts to the climate change through emission of greenhouse gases.At present,the carbon emission measurement and the screening of the strategies for corresponding energy-saving carbon emissions reduction is one of the research hotspot in this region.As the largest agricultural country worldwide,China's carbon emission from agricultural production processes can not be ignored.Consequently,to develop low-carbon agriculture,reduce agricultural greenhouse gas emission and improve agricultural ecological environment are the basis of developing in sustainable way and the scientific basis for the decision-makers to implement effective emission reduction policies In this study,based on the current situation of agricultural production,relying on agricultural carbon footprint theory,emergy analysis theory,index decomposition theory and environmental Kuznets curve hypothesis,the author selected two spatial scales to study the quantification and assessment of agricultural greenhouse gas emissions:municipal level and site scale level.The present study will provide the technical support for the energy-saving and carbon emissions reduction in agricultural production.The main results and conclusions obtained in this study are as following:(1)In this study,a small city(Chizhou)which is a typical agriculture city with a low carbon base is taken as an example.Based on the estimation method provided by the IPCC,and list protocol standard by the WRI/WBCSD,the time series municipal greenhouse gas list of single-path production boundary is compiled,and the greenhouse gas is reduced by the list which make contributions to help make low-carbon decisions.The results indicated that,the carbon emission intensities(per GDP GHG emissions)in Chizhou decreased year by year from 32.75 t CO2-eq/million in 2010 to 25.37 t CO2-eq/million in 2013.In addition,the per capita emissions increased year by year from 9.07 t CO2-eq/in 2010 to 11.97 t CO2-eq/in 2013.In fact,CO2 emissions were almost produced by sectors of energy combustion.Raw coal were the top fossil fuels and nearly 60%of the CO2 emission from energy consumption was caused by the traditional industry.In terms of CO2-eq,while CH4 and N2O emissions have come mainly from agriculture,accounting for 84%and 40%respectively.Moreover,the emission came from crop production was higher than that of the animal husbandry.Moreover,the result indicated that although Chizhou was a relatively low-carbon city in terms of per capita emission,however,in order to reduce the total amount of greenhouse gases,local actual conditions should be considered,including energy structure optimization,industrial adjustment,implementation of circular economy,and capacity building.Moreover,the analysis showed that comparing with geographical boundary,setting the system boundary based on single process standard could provide scientific information and incentives to different stakeholders for their carbon emission reduction.In addition,considering integrity and transparency of GHG inventory,and the problem of the lack of data for many activities,policymakers should to develop relevant standards/guidance to improve data integrity and quality.(2)This paper investigated low-carbon crop production in chizhou city,and revealed the socioeconomic drivers of environmental pressures of crop production during the period of 2004-2015 for carbon footprint,nitrogen footprint and gray water footprint.It is pointed out that the greenhouse gas emission reduction is not incompatible with the increase of production,and the investment agriculture and the improved technology were the high-cost effective ways to reduce the emission.In this study,Life Cycle Assessment was used to quantify greenhouse gas emissions,nitrogen emissions and water environmental impacts of crop production and management in urban areas.The results showed that per t crop produced in the region would produce a carbon footprint of 0.9 t CO2-eq,accompanied by nitrogen emissions from 5.7 kg N-eq and dilution of 287.06 m3 water resources.The results also indicated that Chizhou's increased crop production output was not always positively correlated with an increased environmental pressures.Strong decoupling was the main tendency between carbon footprint(CF)and crop production;a strong decoupling trend occurred more in the analysis of gray water footprint(GWF)from crop production;and decoupling nitrogen footprint(NF)from crop production in a change from expansive coupling to strong decoupling.However,decoupling stability coefficients show that the threat of high-carbon-emission and high-material-input crop production does exist.The main direct contributors,from the material inputs perspective,to the overall change of CF was the nitrogen fertilizer,accounted for 31%.And the most significant contributor to the change of NF was NH3 volatilization from paddy fields associated with N fertilizer applications,accounted for 67%.In general,investment,technology effect along with urbanization process accelerated low-carbon and friendly environmental crop production in Chizhou,while agricultural economic level and population size effect makes the contrary contribution.In this light,we suggest approaches for policy makers to improve innovative technology and substantial investment in cities.At the same time,the impact factors of technology improvement have not been expected to fully play its potential effect on reducing crop production footprint,and a more innovative development method should be sought.The study also showed that the technical requirements for optimizing the application of nitrogen fertilizer were still present urgent needs to reduce the carbon footprint and environmental impact.(3)Biochar soil amendment had been increasingly advocated for improving crop productivity and reducing carbon footprint in agriculture worldwide.However,the long term benefits of biochar application with farming systems had not been thoroughly understood.This study were quantified and assessed carbon footprint,emergy and economic benefits of rice and wheat production throughout 6 rotation years following a single biochar amendment in a rice paddy from southeastern China.Apparently,biochar amendments resulted in a yield increase of rice and wheat by 9-13%and 17-36%,respectively,over the conventional system during 2010-2014."With biochar amendment,plant N concentration was decreased by 3%and 38%on average for rice and wheat crop,respectively,during 2012 to 2015.Similarly,plant P and K concentration were also observed to reduce at varying degrees.Thus,the results showed that the carbon footprint of the unit crop production reduced 10-19%.And considered the carbon sequestration and mitigation of straw biochar amendment,the overall carbon sink was from 66 t CO2-eq ha-1 to 102.6 t CO2-eq ha-1.Using the data from farm inventory,the quantified emergy indices included grain outputs,unit emergy value,and relative percentage of free renewable resources,environmental loading ratio,emergy yield ratio,and emergy sustainability index(ESI).The results indicated contrasting differences in these emergy values between biochar amended and unamended production systems over the 6 years.The overall emergy efficiency of rice and wheat productions in biochar amended system were higher by 11-28%and 15-47%,respectively,than that of unamended one of which the production being highly resource intensive.Furthermore,over the six year following a single application,the ESI values showed considerable variation in the unamended system but consistently increasing in the amended system.The biochar amended system exerted significantly higher energy and economic return than the unamended one.Nonetheless,there was a tradeoff between rice and wheat in grain yield and net economic gain.Overall,biochar amendment could be a viable measure to improve the resilience of grain production while to reduce resource intensity and environment impacts in paddy soil from China.This thesis compiled a complete and transparent GHG inventory for a Chinese city.The accuracy levels of the data sources were assessed in a consistent manner,in order to identify important mitigation option in city level,and also to provide basic information for policy makers.And the driving forces that affect carbon emissions and other environmental impacts of crop production were identify and decomposed by the LMDI method,and pointed out that improving innovative technology and substantial investment were cost-effective options that to further promote environmental conservation while increase crop yields.At the same time,the carbon footprint and emergy balance for rice and wheat rotation system between biochar amended and non-amended system throughout 6-yrs following a single application in a rice paddy from China was quantified,and pointed out that the upscaling of biochar use could be a measure to boost grain production while minimize environmental impacts from China's agriculture sector.Low carbon production and consumption policy and marketing mechanism should be developed to cut down carbon emissions from agricultural sector. |
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