Carbon Footprint Of Banana Plantations And County Scale Farmland In Hainan Province

With the concept of"carbon peaking"and"carbon neutralization"put forward,the regional carbon cycle has been highly valued.As an important type of terrestrial ecosystem,farmland ecosystem is disturbed by both natural factors and human activities,showing the dual characteristics of carbon source and carbon sink.It is still controversial whether it is a net carbon source or a net carbon sink.Hainan Island is located in the tropics,which is the National Tropical modern agricultural base and Tropical Agricultural Science Research Center.The national ecological civilization Experimental Zone（Hainan）implementation plan proposes to build Hainan into an ecological value realization mechanism experimental zone.Banana orchard is an important type of farmland ecosystem in tropical areas,which has significant regional characteristics.However,there are few studies on the carbon cycle of banana orchard ecosystem at home and abroad.Based on this,this study selected Chengmai County as the research target,based on the life cycle theory field research,to evaluate the carbon emissions and carbon absorption of banana production process.Based on the data of farmland production input and crop yield at county level in Hainan Island from 1999 to 2018,the carbon footprint model of farmland ecosystem was constructed The purpose of this study is to provide theoretical basis and data support for the development of tropical high-efficiency agriculture in Hainan and the construction of national ecological civilization experimental zone.The main results are as follows（1）There is a significant difference in greenhouse gas emissions between emperor banana and Brazil banana.The carbon emission per unit area of emperor banana is lower than that of Brazil banana,but the carbon emission per unit output is higher.Fertilization contributed 86.33%and 78.68%of greenhouse gas emissions in the production process of emperor banana and Brazil banana.Among them,N₂O emissions caused by N fertilizer and compound fertilizer containing N were the most important sources of greenhouse gas emissions in the production process of banana.（2）The results showed that the moisture content and carbon content of each organ of emperor banana and Brazil banana were similar,and the fruit was the organ with the strongest carbon sink capacity in banana plant.The carbon sequestration per plant and per unit area of emperor banana were far lower than Brazil banana,which was related to the large difference of biomass between the two kinds of banana.The content of soil organic carbon in inter row and inter plant decreased with the increase of depth,and the content of soil organic carbon in inter row was higher than that in inter plant.After two years of banana planting,the content of soil organic carbon in inter row and inter plant increased,indicating that the soil of banana garden also played a role of carbon sink.（3）The results show that the ecosystem of banana plantations has the characteristics of high carbon emission and high carbon fixation.The carbon fixation of emperor banana plantations and Brazil banana plantations in Chengmai County is higher than that of carbon emission,which shows as net carbon sink.The net carbon sink is 0.94 t CO₂eq·hm^-2 and1.63 t CO₂eq·hm^-2,respectively.The results showed that banana planting process did not increase greenhouse gases in the air,and played an ecological barrier role,but the net carbon sink of the two types of banana plantations were small,so the carbon sink function was not stable.（4）From the perspective of time,the growth rate of carbon emission of farmland ecosystem in Hainan Island in recent 20 years showed a trend of first fast and then slow.Soil respiration and CH₄ emission from paddy field are the main factors of carbon emission from farmland ecosystem in Hainan Island.The input of pesticides and chemical fertilizers and the rapid growth of N₂O emission from farmland contribute to the continuous increase of carbon emission.The carbon absorption of farmland ecosystem in Hainan Island first increased and then decreased.The adjustment of agricultural industrial structure is the main reason for the overall decline of carbon absorption of farmland.The carbon footprint of farmland ecosystem fluctuated first and then increased.The fluctuation period was from 1999 to 2013,and the change trend of carbon footprint was unstable.The continuous growth period was from 2014to 2018.In 2016,the farmland ecosystem of Hainan Island changed from carbon sink to carbon source.（5）From the perspective of space,affected by the difference of agricultural development level,the total carbon emission,carbon emission per unit area,total carbon absorption,carbon absorption per unit area and carbon footprint of farmland ecosystem in Hainan Island in recent 20 years are higher in the surrounding coastal areas and lower in the central inland areas.Only the spatial distribution of carbon footprint per unit area is higher in the East and lower in the West.In general,in recent 20 years,the carbon emission per unit area of farmland ecosystem in Hainan Island has been increasing,the carbon absorption per unit area has been decreasing,and the carbon footprint per unit area has increased significantly.