山区县域近40年耕地土壤有机质的时空变化特征——以湖南省吉首市为例

Spatiotemporal variation in soil organic matter of cultivated land in a mountainous county over the past nearly 40 years：A case study of Jishou City，Hunan Province，China

关键词:  土壤有机质  时空变化  空间插值  吉首市

Key words:  soil organic matter  spatiotemporal variation  spatial interpolation  Jishou City

摘要:

【目的】 土壤有机质（SOM）是表征耕地质量与土壤健康状况的重要指标，其长期变化特征对区域土壤资源评价与管理具有重要参考价值。【方法】 文章以湖南省吉首市为研究区，基于第二次全国土壤普查（二普）491个剖面样点数据与第三次全国国土调查（三调）417个表层样点数据，通过将二普剖面点位不同发生层的SOM按其发生层厚度加权处理到0~20 cm、空间插值与统计分析，分析近40年耕地SOM含量的时空变化特征。【结果】 （1）吉首市二普与三调时期耕地土壤有机质均表现为强变异性。（2）两个时期研究区土壤有机质空间结构性减弱、随机变异增强。（3）近40年来，研究区耕地土壤有机质总体空间分布格局保持“西高东低”的基本特征；约74.43%的耕地土壤有机质含量降低，其中47.43%的耕地降幅集中在5g/kg以内；采样点空间分布差异、高有机质耕地向非农用地转化、潜育型水稻土面积缩减及施肥方式由有机肥主导向化肥主导转变是耕地土壤有机质下降的重要原因。【结论】 在空间分布格局总体稳定的背景下，采样点空间分布差异、城市化导致的高有机质含量耕地的减少及土壤类型变化对县域尺度SOM的时空特征产生了重要影响。研究结果可望为山区县级尺度土壤资源精准管理、农业绿色转型及生态安全维护提供数据参考。

Abstract:

[Purpose] Soil organic matter （SOM） is a key indicator of cultivated land quality and soil health，and its long-term dynamics provide essential information for regional soil resource assessment and management.[Method] This study investigated the spatiotemporal variation in SOM content of cultivated land over the past nearly 40 years in Jishou City，Hunan Province，China，based on data from 491 soil profile sites collected during the Second National Soil Survey and 417 topsoil sampling sites from the Third National Land Resource Survey. The SOM contents of different genetic horizons in the soil profiles from the Second National Soil Survey were transformed to the 0-20 cm layer using a thickness-weighted approach，and spatial interpolation and statistical analyses were subsequently conducted.[Result] （1） SOM in cultivated land in Jishou City remained exhibited high variability during both the Second National Soil Survey and the Third National Land Resource Survey. （2） In both periods，the spatial structure of SOM in the study area weakened，while random variability increased. （3） Over the past 40 years，the overall spatial distribution pattern of SOM in the study area maintained the basic characteristic of higher values in the west and lower values in the east. Approximately 74.43% of the cultivated land in the study area exhibited a decline in SOM content，of which about 47.43% showed a decrease of less than 5 g/kg. Key factors contributing to the decline in arable SOM included spatial variation in sampling points，the conversion of high-organic-matter farmland to non-agricultural land，the reduction in the area of latent-development paddy soils，and the shift in fertilization practices from organic fertilizer-dominated to chemical fertilizer-dominated.[Conclusion] Against the background of a relatively stable spatial distribution pattern，differences in sampling point distribution，the reduction of high-SOM cultivated land driven by urbanization，and changes in soil types jointly exert important influences on the spatiotemporal characteristics of SOM at the county scale. These findings provide scientific support for precise soil resource management，green agricultural transformation，and ecological security maintenance in mountainous counties.