Influencing factors on soil organic carbon density in seven major agricultural regions in China
In order to explore the key factors affecting the spatial layout of Soil Organic Carbon Density(SOCD)in cultivated land,based on the"China High Resolution National Soil Information Grid Basic Attribute Dataset(2010-2018)",taking agricultural area as the research unit,hierarchical regression model and spatial regression model were established to analyze the relationship between hydrothermal condition,vegetation,fertilization and straw returning and SOCD of cultivated land.The results show that:1)The distribution of SOCD in cultivated land showed great differences among all agricultural regions in China.The paddy field SOCD in desendding order is Northeast,South China,the Middle and Lower reaches of the Yangtze River,Southwest,Huang-Huai-Hai,Gan-Xin and Loess Plateau region.The SOCD of dry farm in descending is Northeast,South China,Southwest,the Middle and Lower reaches of the Yangtze River,Gan-Xin,Loess Plateau and Huang-Huai-Hai region.The highest values were observed in the Northeast region(paddy field 7.60±2.39,dry farm 6.58±2.75),while the lower values were observed in the Gan-Xin,Loess Plateau,and Huang-Huai-Hai region(paddy field 3.08±1.29,3.09±0.38,and 3.15±0.43,respectively,while dry farm 3.24±1.27,3.11±0.97,and 2.78±0.36,respectively).2)According to the results of Hierarchical Model I,natural factors play a dominant role in the spatial difference of soil organic carbon density of cultivated land in most agricultural regions(R2＞0.5),and the interpretation level of the spatial difference of SOCD in all agricultural regions increased to different degrees with the addition of human factors in the hierarchical regression model Ⅱ,among which the Huang-Huai-Hai region was the most significant(△ R2=0.152,P=0.001＜0.01).3)Through the model parameter test,the linear regression model was adopted in the Middle and Lower reaches of the Yangtze River,the spatial error model was adopted in the Northeast region,and the spatial lag model was adopted in other regions.4)There are both commonality and difference in the influence mechanism of SOCD in different agricultural regions.The altitude(X5)and straw returning area(Z7)have positive effects on SOCD in all agricultural regions(corresponding coefficients of X5,Z7 in all regions are＞0).The effects of hydrothermal and vegetation conditions,soil erosion,fertilizer application,irrigation,agricultural machinery use and grain yield on SOCD of cultivated land in different agricultural regions were different.To sum up,the spatial distribution of SOCD in cultivated land varies greatly across the country,and the factors affecting SOCD of cultivated land in different agricultural regions are different.Soil organic carbon sequestration strategies for cultivated land should be adopted according to the climate and land use conditions of different agricultural regions.Soil amendments such as biochar should be used in the Middle and Lower reaches of the Yangtze River,South China and Southwest China,and precise proportional fertilization should be promoted;soil amendments and conservation tillage techniques should be adopted in the Northeast region,and precise proportional fertilization and irrigation should be promoted in the Huang-Huai-Hai region and the Loess Plateau region.In addition,all agricultural regions in the country are encouraged to implement straw returning to the field and continuously improve the method of straw returning to the field to promote soil health and sustainable agricultural development.
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