Analysis Of Soil Organic Carbon Sequestration Potential And Carbon Footprint Of Citrus Orchards In The Three Gorges Reservoir Area

As an important cash crop in the Three Gorges reservoir area,citrus is a core pillar supporting local economic development.In recent years,due to the development of the citrus industry,the problem of excessive application of chemical fertilizers and insufficient application of organic fertilizers in China’s citrus orchards has gradually come to the fore,coupled with the fact that the Three Gorges reservoir area has a lot of sloping land,high rainfall and serious soil and water fertilizer loss,in order to maintain high citrus yields and reduce nutrient losses caused by fertilizer loss,the amount of chemical fertilizer input is much higher than in other areas of China,resulting in a large loss of organic carbon in the citrus orchards of the Three Gorges reservoir area and an increase in greenhouse gas This has led to a large loss of organic carbon and increased greenhouse gas emissions in the Three Gorges Reservoir area,hindering the green and sustainable development of the citrus industry in the Three Gorges Reservoir.Organic fertilizer and green manure,as the main measures of"organic replacement of fruits,vegetables and tea",have not been studied enough for their effects on soil carbon sequestration and carbon emission in citrus orchards,which limits the development of carbon balance in citrus orchards.Therefore,this paper takes Zhong County,the main county of citrus cultivation in the Three Gorges reservoir area,as an example.The carbon sequestration rate of organic material（organic fertilizer and green manure）was quantified by means of meta-analysis;information on citrus orchard management was collected through questionnaire surveys,and the carbon footprint of citrus orchards managed by farmers and recommended by experts was calculated by means of life cycle assessment.The main findings of this paper are shown below:（1）Soil testing and ROTHC modelling were used to determine the current status of soil carbon and nitrogen and the carbon sequestration potential of citrus orchards in Zhong County by visiting and sampling citrus orchards throughout the county.The results of the study revealed that only 19.42%of the citrus orchards in Zhong County were suitable for citrus growth in terms of soil p H,45.75%of the soils were deficient in organic matter and 51.37%of the soils were low in total nitrogen.The application of organic fertilizer and green manure increased the soil organic matter content by16.90%and 8.71%,and the soil total nitrogen content by 18.52%and 11.25%respectively.Soil organic carbon pools decreased by 4.82 t ha^-1 after 50 years of fertilizer application only,increased by 3.98 t ha^-1 with green manure,increased by1.62 t ha^-1 with organic fertilizer and increased by 12.86 t ha^-1 with both organic and green manure.soil carbon content increased continuously with other management except for fertilizer application only.（2）SOC and STN accumulation rates due to the presence of organic fertilizers and cover crops in orchards were quantified by global Meta-analysis.SOC and STN storage increased in 87.32%and 79.70%of the studies compared to fertilizer input management.The overall mean annual rate of increase for organic fertilizer was 3.60Mg C ha^-1 and 0.39 Mg N ha^-1 compared to 1.16 Mg C ha^-1 and 0.14 Mg N ha^-1 for cover crops.The rate of sequestration was related to the year of application,initial soil carbon and nitrogen content,the amount of organic fertilizer applied and the climate of the study area.The largest increases in SOC and STN occurred in the first four years of organic fertilizer or cover crop acclimatization.Organic fertilizer and cover cropping management in orchards was more favorable to annual SOC and STN accumulation under lower than high temperature conditions.（3）Through questionnaire research in Zhong County citrus orchards,the impact of organic material inputs on the carbon footprint of citrus orchards was studied by using the life cycle assessment method,and the results showed that:compared with orchards in other parts of the world,citrus yields in the study area were low,farm carbon footprint and product carbon footprint were high,carbon footprint and carbon effectiveness composition were mainly influenced by fertilizer,especially nitrogen fertilizer,and carbon footprint under different management methods was significantly different.The carbon footprint and carbon effectiveness components are mainly influenced by fertilizer,especially nitrogen fertilizer,and there are significant differences in carbon footprint between management practices,with farmers managing a carbon footprint of 11.56 t CO₂eq ha^-1 and 0.83 t CO₂eq t^-1 and experts recommending fertilizer management with a carbon footprint of 6.57 t CO2eq ha^-1and 0.40 t CO₂ eq t^-1,Reduced carbon footprint by approximately 47.49%.The carbon footprint of early-maturing citrus is 11.50 t CO₂eq ha^-1 and 0.80 t CO₂eq t^-1,while the carbon footprint of late-maturing citrus is 12.34 t CO2eq ha^-1 and 0.99 t CO₂eq t^-1.Early-maturing citrus has a lower carbon footprint than late-maturing citrus,and the carbon effectiveness of early-maturing citrus is higher,allowing farmers to reap higher economic benefits.In addition to this,the use of organic fertilizers by farmers leads to more greenhouse gas emissions.In conclusion,organic fertilizers and green manures can effectively increase soil organic carbon in citrus orchards,and have a significant effect on increasing soil carbon sequestration potential and rate.In summary,organic fertilizer and green manure can effectively increase soil organic carbon in citrus orchards,and have a significant effect on increasing soil carbon sequestration potential and sequestration rate.Organic fertilizer does not have a positive effect on reducing greenhouse gas emissions,and the carbon footprint reduction potential of citrus orchards is huge and can effectively mitigate agricultural greenhouse gas emissions.