| High-intensity agricultural activities affect various ecosystem services by affecting the soil carbon-nitrogen water cycle and the consumption of energy and resources,and quantifying the impact of agricultural activities on the ecological environment is an important premise for exploring sustainable agricultural development.In this thesis,the combination of emission factor and model simulation methods was employed to optimize the quantification methodology of carbon,nitrogen and water footprints in crop production.Based on the national statistical yearbook dataset,literature-based dataset and high-resolution crop cultivation dataset,the carbon,nitrogen,and water footprints of three major grain crops in China and their constituent characteristics were studied,and the spatial heterogeneity was explored.Finally,the integrated analysis method was used to comprehensively quantify the impact of crop production on the ecological environment from three aspects of greenhouse gas emissions,reactive nitrogen loss and water resource consumption,and explore the threats of crop production on human health and ecosystems and the consumption of resources.The main findings were as follows:1.Based on statistical yearbook data,crop cultivation spatial dataset and soil spatial dataset,a grain crop production database was constructed,mainly including crop yield,sown area,fertilizer application rate,the amounts of agricultural film use and pesticide input,irrigation,mechanical fuel use,spatial distribution of crop planting area and soil properties(sand,silt and clay content,total nitrogen,bulk density,soil organic matter,pH,etc.).This database was used to quantify the carbon and nitrogen footprints of major grain crop production.A farmland NH3 volatilization database was established through literature collection,including 964 sets of NH3 emissions observation data,and also including soil properties(soil organic carbon content,total nitrogen,sand content,silt content,clay content,soil bulk density and pH),meteorological data(average annual average annual precipitation),fertilizer amount,fertilizer type,fertilization frequency,and crop planting data(crop type,planting date,transplanting date and harvest date),which was used to establish an empirical model of NH3 volatilization.A high-spatial-resolution meteorological database was obtained by spatial interpolation of the national meteorological station data obtained from China Meteorological Data Service Center using Tyson polygon method.The database was used to assess the water footprint of grain crops.2.The carbon footprints(CFs)of major grain crop production in China in 2017 was quantified using the life cycle assessment-CF methodology.The results showed that the area-scaled and yield-scaled CFs of paddy rice production were 9159 kg CO2-eq ha-1 and 1.32 kg CO2-eq kg-1,respectively,which was higher than that of corn(3934 kg CO2-eq ha-1 and 0.67 kg CO2-eq kg-1)and wheat production(2786 kg CO2-eq ha-1 and 0.52 kg CO2-eq kg-1).The main contributors of the CF of rice production was methane emissions,which contributed up to 54%;and the fertilizer use was the main source of the CFs of corn and wheat production.contributing 51%and 42%,respectively.Comparing different agro-regions.it was found that the CFs of rice and corn production were the highest in Gansu-Xinjiang agro-region,which was 1.59 and 0.78 kg CO2-eq kg-1,while that of wheat production was highest in Northeast agro-region(0.62 kg CO2-eq kg-1).The total greenhouse gas emissions of the three crops production were 498.86 Mt CO2-eq,of which rice production accounted for 56%,and corn and wheat production accounted for 30%and 14%respectively.3.Based on the methodology of nitrogen footprint(NF),the reactive nitrogen losses in grain crop production were quantified including ammonia volatilization,nitrous oxide emissions,nitrogen leaching and runoff losses,and nitrogen oxide emissions,and the NF of grain crop production was analyzed.First of all,because there was no suitable model for calculating ammonia volatilization in farmland in China,a linear regression method was conducted to establish a multiple regression ammonia volatilization agro-region model based on the NH3 volatilization database,which was then validated by independent measurements.The validation results showed that the established model can precisely estimate ammonia volatilization in Chinese farmland without bias.The Gansu-Xinjiang&Qinghai-Tibet model had the best performance with a R2 of 0.92,a simulation efficiency of 72%,and a relative root mean square error of 44%,and there was no significant difference between the simulated and the measured values.Then,using the established model,as well as the emission factors and models developed by previous studies,the NF of major grain crop production in 2017 was calculated.Wheat production had the highest area-and yield-scaled NF being 100.04 kg N ha-1 and 18.25 g N kg-1,followed by corn production(84.42 kg N ha-1 and 13.81 g N kg-1);the NF of rice production was the lowest at 84.40 kg N ha-1 and 12.20 g N kg-1.Ammonia volatilization was the main reactive nitrogen loss in rice production,while the main sources of reactive nitrogen loss for wheat and corn production were nitrogen runoff and leaching,which contributed up to 30%.The areas with great loss of reactive nitrogen in rice production were mainly concentrated in the Yangtze River and Southwest agro-regions in China,and the Huang-Huai-Hai and Northeast agro-regions had the highest reactive nitrogen loss in corn production.The area with high losses of reactive nitrogen in wheat production was the Huang-Huai-Hai agro-region.The total losses of reactive nitrogen in the three crops production was 8.63 Tg N(95%confidence interval of 7.70～9.94 Tg N),of which corn production was the highest at 3.58 Tg N,followed by rice production at 2.60 Tg N.The lowest losses of reactive nitrogen were found in wheat production,accounting for 28%of the total.4.Combining the Penman formula and the water footprint(WF)methodology,the blue,green and gray WFs of rice,corn and wheat production in 2017 were estimated in China using the meteorological spatial database and nitrogen fertilizer input data.The study found that the area-scaled WF of corn production was 8355 m3 ha-1,which was higher than that of wheat(7487 m3 ha-1)and rice(6547 m3 ha-1).The yield-scaled WFs of wheat,corn and rice production were 1.43,1.36 and 1.09 m3 kg-1,respectively.The green WF of rice production accounted for the highest proportion being 41%of the WF,and the gray WFs contributed most at around 50%in corn and wheat production.In terms of spatial distribution,the WF of wheat production was the highest in Inner Mongolia and along the Great Wall agro-region at 4.85 m3 kg-1,and the WFs of corn and rice production were the highest in Qinghai-Tibet agro-region,at 2.16 m3 kg-1 and 1.63 m3 kg-1,respectively.The total WFs of the three grain crops production were 778.2 G m3,of which rice production accounted for 30%,and corn and wheat production accounted for 46%and 24%,respectively.5.Based on the Endpoint modelling environmental assessment method,an integrated footprint method for evaluating the comprehensive eco-environmental effects of crop production was developed to evaluate greenhouse gas emissions,reactive nitrogen loss and water resource consumption from three perspectives including human health,ecosystem impact and resource consumption.The results showed that water loss accounted for the highest proportion at 66%～82%of the overall eco-environment impact of the three crops production,followed by reactive nitrogen loss(20%～12%),and the greenhouse effect contributed relatively small(6%～17%).Comparing the three perspectives of human health,ecosystem impact and resource consumption,resource consumption poses the highest risks for three grain crops production.In addition to resource consumption,the eco-environmental risk of rice production was mainly a threat to human health.In the integrated footprint of corn and wheat production,the risk of human health was high and the threat to ecosystems was low.Comparing different agro-regions,it was found that the regions with the highest eco-environmental risk of wheat production were Inner Mongolia and along the Great Wall and South agro-regions,and the agro-regions of Qinghai-Tibet and South had the highest risk in corn production.In general,the eco-environmental risks of crop production in the northern region were higher than those in the southern region.Inner Mongolia and along the Great Wall agro-region had the highest risks in the northern regions,while South agro-region had the highest risk in the southern regions.In summary,this thesis developed carbon,nitrogen,and water footprint methodologies suitable for the grain crops production in China,and optimized the parameters required to calculate the footprints.Based on the established database,the carbon,nitrogen and water footprints of China’s major grain crops production were quantified,and the contributors were assessed.The integrated footprints were calculated to determine the relative risks of greenhouse gas emissions,reactive nitrogen loss and water consumption,and a highspatial-resolution distribution map of the eco-environment risks of grain crop production was drawn.The results by this thesis can provide methodological basis and scientific reference for technology selection and policy development of agricultural sustainable development in China. |
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