压砂地土壤水分时空变异理论与模型研究

Gravel-mulched field is a unique mode of conservation tillage, which depends on natural precipitation, created by the working people in arid regions, who use gravel as covering materials. The unique hydrological process and the interaction among different hydrological factors lead to the complexity of the temporal and spatial variability of soil moisture and affect the application of the universal theory. It has become one of the problems need to be resolved urgently in disciplines, such as agriculture, soil and water science. Regarding the soil hydraulic properties and changes of soil moisture in farmland after the pressure sand as a starting point, based on the method of combining theoretical analysis, numerical simulation and experimental study, this project makes a comparative study of quantitative experiment and simulation on the bare on different planting years and different planting season in gravel-mulched field, aming at revealing the spatial variability law of soil hydraulic properties under the conditions of pressure sand, and vertical heterogeneity, spatial variability of soil moisture and understanding the temporal distribution pattern of the soil moisture in gravel-mulched field. What's more, the paper also studies the temporal and spatial variation regularity and response mode of soil moisture in gravel-mulched field under the conditions of different precipitation pulses, then sets up spatial and temporal prediction model of soil moisture in gravel-mulched field and calibrates the best sand particle size and cover thickness in gravel-mulched field, which will pave the way for the theoretical foundation of the agricultural water regulation and improve precipitation transforming use efficiency in gravel-mulched field.

压砂地是旱区劳动人民利用砂石作为覆盖材料，依赖天然降水创造出的一种独特的保护性耕作模式。它由于具有独特的水文过程，不同水文要素间相互影响、相互作用，导致了土壤水分时空变异的复杂性，也影响到普适论的应用，已成为农业、土壤和水科学等学科迫切需要解决的问题之一。以压砂后农田土壤水力特性、土壤水分的变化为出发点，运用理论分析、数值模拟及实验研究相结合的方法，通过对裸地、不同种植年限和不同种植季节压砂地的定量实验和模拟对比研究，揭示压砂条件下土壤水力特性的空间变异规律，土壤水分垂向异质性、空间变异特征，理解压砂地土壤水分的时间分布格局，进而研究不同降水脉动条件下压砂地土壤水分的时空变异规律及响应模式，建立压砂地土壤水分的时空预测模型，率定出最佳的砂石粒径和覆盖厚度，为压砂地农业水分调控、降水资源有效涵养和利用提供理论依据。

本项目以我国西北旱区有着300多年历史的压砂地为研究对象,在查阅国内外相关文献资料的基础上，采用实验、数值模拟和理论研究相结合、以实验为主的技术路线，通过模拟实验，研究了不均一介质覆盖条件下，压砂地种植年限和降雨强度对土壤水分入渗过程的影响，建立了压砂地土壤水分入渗模型；采用HYDRUS-1D软件，模拟了不同土壤质地、初始含水率、压力水头、砂层埋深和砂层厚度条件下的稳渗过程，提出了由土壤物理特性参数进气值倒数估算进水吸力的计算公式；在Green-Ampt入渗模型基础上，引入导水度系数(小于1)来量化上层土壤的导水程度，建立了改进的夹砂层土壤Green-Ampt入渗模型。研究了压砂厚度和粒径对土壤水分蒸发和盐分迁移的规律，率定出覆盖10cm厚的细砂粒径级配最优。 .通过野外长期监测试验，运用地统计学和经典统计学方法，研究了不同种植年限压砂地的土壤水分空间变异规律和分形维数，基于GS+9.0软件，构建其半方差函数模型，揭示了土壤水分垂向异质性、空间变异特征；应用Moran的I指数，研究了压砂地0-50cm土壤水分的空间自相关性及土壤水分随取样幅度的变化规律，探讨了土壤水分空间变异性对尺度变化的响应关系，发现8 m为较合理的采样间距，可以代表土壤水分的平均状况；研究了降雨脉动7.1mm和1.9mm条件下土壤含水率随时间的变异规律及土壤水分的空间变异特征；在应用Spearman秩次分析法研究土壤水分的时空稳定性的基础上，确定了样地内的代表测点，探讨了空间样点代表性的评价与计算方法，并建立了测点土壤水分与样地平均土壤水分的预测模型，理清了压砂地土壤水分的时间分布格局，改进了监测压砂地土壤水分的方法。以上研究为进一步提高压砂地农业水分调控、降水资源有效涵养和利用奠定了科学基础，具有十分重要的科学价值和生产实际意义。项目研究成果已公开发表学术论文35篇，其中SCI收录3篇，EI收录10篇；结合该项目研究，培养硕士研究生9名。