宁夏中部旱区压砂地土壤干燥化特征及驱动机制

Soil moisture deficit and soil desiccation in the gravel mulched field appeared as the lifetime of service increasing. Field investigation, fixed-site monitoring and laboratory simulation were combined to research spatial-temporal variability of soil moisture in the gravel mulched field of the central arid regions of Ningxia with the statistical analysis, numberical simulation and geographic information system. The project would explore the variation pattern, source and driving factors for the soil moisture, determine quantitative indicator system of soil desiccation, analyze distribution characteristic of dried soil layer. The project would clarify the response of soil moisture variability to climate, topography, vegetation and so on. The suitable size and length of gravel particle would be revealed based on the capacity of soil moisture. Then the spatial databases of soil moisture indexes would be established in the gravel mulched field, and the evolution mechanism of soil desiccation would be revealed. The achievements of the research could contribute to prevent the degradation of gravel mulched field and extend the lifetime of service. Meanwhile, the project could help to scientifically evaluate the impact of gravel mulching on the water cycle process of ecosystems in arid area, and provide the train of thought for the reduction of soil desiccation.

针对随压砂地使用年限增加其土壤水分快速下降、土壤干燥化加剧的现象，以宁夏中部旱区压砂土壤为研究对象，结合野外调查、定位监测和室内模拟等手段，借助统计分析、模型分析和GIS方法，深入开展宁夏中部旱区压砂土壤水分时空变化特征研究，探究其变化规律、驱动因子及分布特征。初步建立压砂土壤干燥化量化指标体系，分析压砂地干燥化程度、土壤干层分布深度及广度，阐明压砂土壤干燥化过程中土壤水分时空变化特征以及其与气候、地形、植被类型等响应程度，提出基于土壤水分安全承载下较为合理的压砂粒径和压砂厚度，建立压砂土壤水分指标空间数据库，揭示压砂土壤干燥化演化过程。研究结果一方面有助于防治研究区压砂地老化、延长其利用年限，另一方面有助于科学评价压砂这一特殊耕作方式对西北旱区生态系统水分循环过程的影响，为减缓压砂地土壤干燥化过程提供思路。

土壤干燥化的产生会导致土地质量下降和林草生长衰败等现象。因此本项目以宁夏中部旱区压砂地为研究对象，通过对压砂地土壤基本物理性质和含水量进行实地观测，借助经典统计学和地统计学方法，选择干燥化指数、干层厚度、干层内平均含水量和干层起始形成深度四个量化指标，建立了压砂土壤干燥化量化指标体系；结果表明土壤容重、总孔隙度、毛管孔隙度和饱和含水量的均值分别为1.38 g•cm-3、47.81%、34.54%和35.63%，除容重属于弱变异性，其余均表现为中等变异性；在0~600 cm的土层中，田间持水量和凋萎系数的均值分别为17.45%和4.89%，表现为中等变异性；研究区内压砂地土壤基本物理性质均存在明显的空间变异特征，其分布格局由结构因素和随机因素共同作用导致。不同植被类型下压砂地土壤含水量在0~600 cm的均值为7.16%，明显低于田间稳定持水量，土壤贮水量和有效贮水量均值分别为591.98 mm和187.09 mm，干燥化程度由强到弱依次为柠条地 > 沙枣地 > 枸杞地 > 草地 > 西瓜地。不同年限下压砂地土壤含水量在0~600 cm的均值为11.24 %，略高于田间稳定持水量和贮水量，但16 a和25 a压砂地的含水量低于田间稳定持水量，土壤贮水量和有效贮水量均值分别为936.11 mm和531.22 mm；不同种植年限下土壤剖面含水量随深度呈先减小后增大最后逐渐平稳的趋势；不同种植年限下压砂地土壤干燥化系数介于70.09 %~162.36 %，均值为114.18 %，平均干层厚度为283.33 cm，随着种植年限的增加，土壤干燥化强度和干层厚度逐渐增加。通过相关性分析对土壤干燥化各指标的影响因子进行筛选，运用GWR模型对土壤干燥化各指标及其主要影响因子进行模型分析，并绘制各因子的回归系数空间分布图，揭示压砂地土壤干燥化的形成原因及其主控因子。