黄土高原丘陵沟壑区典型土地利用类型对土壤含水率与土壤质量的影响研究

Study on the effects of typical land use types on soil water content and soil quality in the hilly and gully areas of the Chinese Loess Plateau

关键词:  黄土高原  土地利用类型  土壤含水率  土壤质量评价

Key words:  Chinese Loess Plateau  land use types  soil water content  soil quality assessment

摘要:

水资源短缺和土壤侵蚀是制约黄土高原地区生态和社会发展的关键问题，明确黄土高原典型土地利用类型土壤含水率和土壤质量的差异，对促进区域生态的可持续发展有重要意义。文章选择了黄土高原丘陵沟壑区4种典型土地利用类型（纯林地、混交林地、草地和耕地），通过定位监测分析土壤含水率变化； 选择了15个土壤质量指标，其中，物理指标为土壤容重、土壤机械组成（黏粒、粉粒、沙粒），化学指标为pH、阳离子交换量、有机质、总碳、全氮、全磷和微生物碳，酶活性指标为土壤脲酶、蔗糖酶、碱性磷酸、葡萄糖酶，利用主成分分析法和模糊隶属函数法，评价土壤质量等级。结果表明：（1）不同土地利用类型土壤含水率由大到小分别为草地 （22.6 mm）、耕地 （20.9 mm）、混交林地 （20.0 mm） 和纯林地 （19.9 mm）（p＜0.05），草地土壤保水性更强；（2）降雨对土壤含水率的影响存在阈值效应，降雨量为10— 30 mm/d时对生长层土壤（50—70 cm）含水率的增加有促进作用；（3）混交林地、纯林地、草地和耕地的土壤质量指数分别为0.57、0.49、0.50和0.38，土壤质量整体中等偏差。这些结果为研究区土壤资源的管理和水资源利用提供了基础数据参考，即与耕地相比，林地对土壤质量有改善作用，然而在生态环境更为脆弱和干旱的地区，则应避免林地的扩张，增加低耗水草地的面积。

Abstract:

Background, aim, and scope The intertwined challenges of water scarcity and soil erosion continue to impede both ecological sustainability and socioeconomic advancement across the Chinese Loess Plateau. Following the launch of the “Grain for Green” initiative, the region has experienced substantial shifts in land use, highlighting the urgent need to elucidate how soil water content and soil quality vary across representative land use categories. This study aimed to evaluate these variations within the hilly-gully region of the Chinese Loess Plateau and to determine the land use configurations most conducive to sustainable vegetation restoration in environments constrained by limited water availability. Materials and methods Field-based investigations were carried out at the Nangou Ecological Experimental Station in Yan’an, Shaanxi Province, situated within the Chinese Loess Plateau. Soil samples were collected to assess both water content and a range of physicochemical properties. Four representative land use types (pure forest land, mixed forest land, grassland, and farmland) were selected as the research objects. Seasonal monitoring of stratified soil moisture levels was conducted from March to October 2022, supplemented by continuous measurements using precision moisture sensors. A total of fifteen soil quality indicators were selected for analysis, including bulk density, particle size distribution (clay, silt, and sand), pH, cation exchange capacity, organic matter, total carbon, total nitrogen, total phosphorus, microbial biomass carbon, and four enzymes (urease, sucrase, alkaline phosphatase, and glucosidase). These parameters were measured to calculate the soil quality index (SQI), aiming to quantify the variation patterns of soil quality across different land-use types. To quantify soil quality, principal component analysis (PCA) in conjunction with the fuzzy membership function method was employed to derive a composite soil quality index and classify quality grades accordingly. Results (1) Statistically significant differences in soil water content were observed among the various land use types (p<0.05), with the descending order being: grassland (22.6 mm)>farmland (20.9 mm)>mixed forest (20.0 mm)>pure forest (19.9 mm); (2) A threshold response to precipitation was identified, whereby daily rainfall events of 10—30 mm/d significantly increased soil moisture levels within the root-active zone (50—70 cm depth); (3) The calculated soil quality indices were 0.57 for mixed forest, 0.49 for pure forest, 0.50 for grassland, and 0.38 for farmland, collectively reflecting a generally suboptimal soil quality status across the study area. Discussion Forested land is characterized by a complex vegetation architecture and extensively developed root systems, both of which contribute to elevated rates of evapotranspiration and substantial canopy interception. These features collectively lead to increased soil water consumption. In contrast, grassland exhibits superior water retention capacity, largely attributable to its dense surface coverage, enhanced rainfall interception, reduced evapotranspiration and surface runoff, along with greater infiltration efficiency. Farmland, in comparison, is subject to intensive anthropogenic disturbance and experiences heightened surface runoff, leading to lower soil moisture levels. Under conditions of limited precipitation, rainfall can offset plant water demand and temporarily enhance soil moisture. However, excessive rainfall often saturates the soil profile and amplifies runoff, thereby diminishing overall soil water storage. The generally poor soil quality observed across the study area is primarily linked to its sandy, porous texture, low cation exchange capacity, and limited ability to retain both water and nutrients. Forested areas, subjected to minimal anthropogenic disturbance, exhibited greater litter accumulation and higher nutrient content in the soil. Notably, mixed forest plots showed more rapid litter decomposition and elevated soil organic matter levels relative to pure forest plots, leading to improved soil quality ratings. Conversely, long-term cultivation practices in farmland intensified human impact and accelerated organic matter mineralization, thereby contributing to a decline in soil quality. Conclusions These results provide essential empirical support for the effective management and sustainable utilization of water and soil resources on the Chinese Loess Plateau. Grassland has been identified as a more appropriate land use option for water-limited regions, while forested land demonstrates greater potential for enhancing soil quality relative to farmland. Recommendations and perspectives Continuous monitoring of soil moisture dynamics and soil quality is essential throughout the process of vegetation restoration, accompanied by timely modifications to vegetation composition as needed. In ecologically vulnerable and arid regions, a strategic combination of controlled afforestation and the expansion of low water-demand grassland is advocated to support the long-term sustainability of both water resources and ecosystem recovery.