Temporal And Spatial Transformation Of Rice Crayfish Field And Its Effect On Soil Organic Carbon

The rice crayfish comprehensive planting and breeding model has expanded rapidly since 2015,and has become one of the common cultivated land use modes in the middle and lower reaches of the Yangtze River in China.Rice crayfish field has gradually become the research object of scientists.In the early stage,scholars mainly focused on the composition and vertical distribution of soil organic carbon in a single rice crayfish field.Then they revealed the impact of planting and breeding time on soil organic carbon in rice crayfish field,and then discussed the impact of rice crayfish model on resource utilization,rice yield and ecological environment.Finally,they found that rice crayfish model promoted soil carbon sequestration.This is in line with the common goal of the world-carbon emission reduction,which is of positive significance for China to achieve the goal of carbon neutrality.However,rice crayfish fields are mostly reclaimed spontaneously by farmers,It is difficult for governments to grasp the spatial changes,and it is more difficult to effectively regulate the scale of rice crayfish field and scientifically guide the development of rice crayfish industry.Therefore,it is urgent to explore the method of high-precision identification of rice crayfish field.In addition,scholars focused on the impact of rice crayfish model and pure rice planting on soil organic carbon content,but ignored the soil characteristics of rice crayfish field transferred from land.Therefore,it is necessary to analyze the content of soil organic carbon on the field surface and shrimp ditch after the transformation of plots with different land use types into rice crayfish field,and try to reveal the impact of the change of rice crayfish field with time.Based on Google Earth engine,this paper uses the 2A remote sensing image data of sentinel-2 multispectral imager from 2016 to 2020,the classification indexes such as spectral features,texture features and topographic features are constructed year by year,and the land use classification results of Qianjiang City,Hubei Province in five years are obtained by using the random forest classification method,the recognition results of rice and shrimp fields in each year are extracted,and the dynamic transformation process between rice and shrimp fields and other land types is obtained.One year,threeyear and five-year rice crayfish fields transferred from fields without water,paddy field,water area,forest land and construction land were selected.The soil samples of field surface and shrimp ditch of rice crayfish field were collected.The content of soil organic carbon was measured by potassium dichromate external heating method,and the characteristics of soil organic carbon content of rice crayfish fields transferred from different land types were analyzed.The conclusions of this study are as follows:(1)From 2016 to 2020,the overall accuracy of land use classification results in Qianjiang City was more than 89%,of which more than 90%in 2016,2017,2018 and 2020;The kappa coefficient of each year is more than 87%,including more than 88%in 2016 and 2017.(2)Rice crayfish field in Qianjiang City is mainly distributed in the northwest,West and central regions of the city,with an area increasing year by year.(3)Paddy fields are concentrated in the west,South and Southeast,and their area proportion has always been the largest;Fields without water is mainly distributed in the north,East and both banks of Dongjing River,and its area proportion is decreasing on the whole;Forest land is mainly distributed on the banks of Dongjing River,Tianguan River,Xijing River and other rivers,and its area accounts for the smallest proportion compared with other land types;The distribution of construction land is scattered,mainly concentrated in urban areas and township centers,and the change range of its floor area is the smallest.(4)Soil organic carbon content of rice crayfish field transformed from different land types is significantly different in the field surface and shrimp ditch surface(020cm)in different planting and breeding years.The difference of soil organic carbon content between field surface and shrimp ditch in the same rice crayfish field is obvious.(5)After other land use types were transformed into rice crayfish field,the number of plots with higher soil organic carbon content than the original land type accounted for 70%of the total sample plots,but different land types had no significant effect on the content of surface soil organic carbon in shrimp ditch(P>0.05).Based on the accurate identification of rice crayfish field,this study creatively proposed to analyze the differences of soil organic carbon content on the field surface and shrimp ditch surface of rice crayfish field transformed from different land use types in different planting and breeding years,and reveal the impact of rice crayfish field on soil organic carbon.This will promote the development of rice crayfish model and rice crayfish industry,help to realize the dynamic monitoring of rice crayfish field and the market prediction and regulation of rice crayfish industry,and provide reference for subsequent relevant research and policy planning.