Distribution Characteristics And Influencing Mechanism Of Soil Organic Carbon In Rice-Crayfish Fields In Qianjiang City

Soil organic carbon change not only affects global climate change,but also is one of the important indicators of soil fertility,which is related to food production and food security.However,soil organic carbon content is not constant,and it fluctuates greatly with perennial cultivation and land use changes.Previous studies mainly focus on traditional crops and land use,with research on new land use modes being relatively scarce.As a new ecological planting model,rice fields have been expanding constantly in the middle and lower reaches of the Yangtze River,driven by green development and economic benefits.The present study investigated the changes in soil organic carbon density,profile depth,and spatial distribution in Qianjiang City,the"hometown of rice-crayfish",through sampling of rice-crayfish fields,forest land,paddy field,and dry land.The study combined data from the second soil census to explore changes in soil organic carbon at different periods,and analyzed the impact of transforming paddy fields into rice-crayfish fields on soil organic carbon.The study explored the mechanism affecting soil organic carbon changes in Qianjiang City based on the changes and spatial distribution characteristics of soil organic carbon in rice-crayfish fields.Based on these findings,suggestions were made for the development of rice-crayfish fields in Qianjiang City to promote sustainable agriculture.Conclusions based on the research content and results,the following conclusions can be drawn:(1)Soil organic carbon showed a decreasing trend with increasing depth,and the highest soil organic carbon was found in rice-crayfish fields,followed by forest land,paddy field and dry land.The surface soil organic carbon content of rice-crayfish fields decreased faster.Soil organic carbon content of rice-crayfish fields was mainly concentrated in the range of 0.87～24.88 g/kg.The density is concentrated in 15.40-53.95t/hm~2.From the perspective of space,the high value areas of soil organic carbon content and carbon density in Qianjiang were mainly distributed in western and southwestern areas,mainly in Zhangjin Town,Yungrhu Management area and other towns,and the land use was mainly in rice and shrimp fields.The low-value areas appeared along the Han River in the north and some areas in the middle,mainly dry land.(2)The soil organic carbon content in the second soil census period was higher than that in 2022,and the area with high value of soil organic carbon was larger than that in2022.The soil organic carbon content of paddy field was the highest in the second soil survey period,and the soil organic carbon content of paddy field in 2022 was higher than that of paddy field,mainly because after the second soil census period,most paddy fields in Qianjiang City were transformed into rice-crayfish fields.The spatial distribution characteristics of soil organic carbon in the second soil census period were similar to those in 2022.The high value areas were mainly concentrated in the southern Zhangjinzhen and Bailu Lake Management area.Low value areas appear in the northern Hanjiang River basin and Dongjing River basin.(3)The unique mechanisms of influence of rice-crayfish fields on organic carbon are mainly reflected in the depth of the profile,the way it is used,and human activities.The results showed that the soil organic carbon content in the surface layer of rice-crayfish fields was higher than that in the deep layer.This was due to the surface soil having a sufficient carbon source and a suitable soil environment.Comparing the second soil survey period and the sampling in 2022,it was found that soil organic carbon in Qianjiang displayed a downward trend.Due to the transformation from paddy fields to rice-crayfish fields after the second soil survey period,the soil organic carbon content in rice-crayfish fields was higher than paddy fields,and the soil organic carbon content in the distribution area of paddy fields showed an increasing trend.However,it has not yet recovered to the level during the second soil survey period.Soil organic carbon content in rice-crayfish fields can be increased by the combination of regular plots,crayfish breeding,straw returning,and irrigation.By increasing carbon source and creating a suitable environment,the soil organic carbon content can be improved.(4)While the development of rice-crayfish fields can bring benefits such as increased soil organic carbon content,improved soil environment,and increased income for local farmers.It is important to carefully consider the life characteristics of crayfish and the local environment before embarking on such a project.This will help to ensure that development is sustainable and benefits both the local community and the environment.