Spatial and Temporal Variation of Soil Carbon and Nitrogen in Typical Counties of North Loess Plateau and Influencing Factors
[Objective]The ecological environment of Loess Plateau is fragile and once the soil quality of cultivated land changes,it will directly affect the level of soil productivity.A long-term cultivated land in Tianzhen County,a typical county in the north of the Loess Plateau,was selected to study the spatiotemporal evolution of soil organic matter and total nitrogen and their influencing factors.[Method]Based on the cultivated land quality data in 1983,2008 and 2019,the temporal and spatial evolution characteristics and distribution patterns of organic matter and total nitrogen in cultivated soil of Tianzhen County were analyzed using GIS and geostatistics methods.[Result](1)In the past 36 years(1983-2019),soil organic matter and total nitrogen content in Tianzhen County showed a significant change characteristic,which increased as a whole and rose rapidly in the later period.The average annual increase of organic matter and total nitrogen content was lower in the early period(1983-2008),showing 0.20 g·kg-1 and 0.01 g·kg-1,respectively,while the number was higher in the late period(2008-2019),showing 0.29 g·kg-1 and 0.03 g·kg-1.In the early stage of the study period,the ratio of carbon to nitrogen showed no significant change,but showed a significant decrease in the late stage,from 9.32 in 1983 to 8.43 in 2019.(2)The semi-analysis of variance(ANOVA)results revealed that over the past 30 years,the block-base ratio of soil organic matter increased from<25%to 49.8%and the block-base ratio of soil total nitrogen increased from<25%to 38.5%.This indicated that the influence of natural factors such as topography was gradually diminished,while the influence of human factors such as fertilizer application was enhanced.(3)The spatial distribution characteristics of soil organic matter and total nitrogen had similar characteristics and showed a pattern of low in the west and high in the east.From 1983 to 2008,the content of soil organic matter showed an overall increasing trend,with a significant increase in the northwest and a slow increase in other regions;total nitrogen increased significantly in the northwest and decreased in the east.Also,from 2008 to 2019,soil organic matter decreased slightly in the south while it increased in other regions;total nitrogen increased significantly in the north but more slowly in other regions.[Conclusion]Over the past 36 years(1983-2019),the soil organic matter and total nitrogen content in Tianzhen County showed an overall upward trend,and factors such as fertilization and straw returning to the field were the main factors leading to the changes in organic matter and total nitrogen content.Combined with the local conditions to increase the application of organic fertilizer,straw returning and rational application of nitrogen fertilizer can quickly improve the soil fertility of cultivated land.Therefore,this study can provide a theoretical basis for improving the quality of cultivated land on the Loess Plateau and protecting the agricultural ecological environment.
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