黄土高原北部典型县域耕地土壤碳氮时空变异特征及影响因素

黄土高原生态环境脆弱，耕地质量的变化直接影响土地生产力的高低。选取其北部典型县域——天镇县，研究长时期耕地土壤有机质和全氮的时空演变规律及其影响因素，为黄土高原耕地质量提升和农业生态环境保护提供理论依据。基于1983年、2008年和2019年耕地质量数据，运用地统计学等方法分析天镇县有机质和全氮的时空演变特征。结果发现：（1）36年（1983—2019年）来，天镇县土壤有机质和全氮含量呈现整体上升、后期快速增加的变化特征。有机质和全氮含量的年均增加量前期（1983—2008年）较低，分别为0.20 g?kg-1和0.01 g?kg-1，在后期（2008—2019年）较高，分别为0.29 g?kg-1和0.03 g?kg-1。碳氮比呈现前期无显著变化，后期显著降低。（2）36年来土壤有机质和全氮的块基比均提升至高于25%，表明地形等自然因素影响逐渐减弱，施肥等人为因素影响增强。（3）土壤有机质和全氮的空间分布特征相似，呈现西部低、东部高的格局，西北部和中部的变化速度快。综上，36年（1983—2019年）来，施肥及秸秆还田等因素是导致天镇县有机质和全氮含量变化的主要因素，因此，结合当地条件增施有机肥、推广秸秆还田并合理施用氮肥能快速提升耕地土壤肥力。

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.