压砂地土壤水热盐耦合迁移机制及调控研究

Gravel-sand mulched field is a unique dry farming conservation tillage mode in northwestern arid region, mulching sand on soil surface changed soil surface configuration and ground roughness and further affected soil pore, reduced wetted cross section, increased crooked degree of pore. All of these lead to that the water, heat and salt transport in gravel-sand mulched field was more complicated than homogeneous soil. More gravel mixed with the soil over time, which had an effect on soil structure, physical properties of soil and hydraulic parameters, and also affected the transfer mechanism of soil water, heat and salt. Thus it was difficult to provide scientific and reasonable explanation and reference for the decision-makers. For this purpose, regarding the change of soil water, heat, salt with gravel mulching as a starting point, quantitative experiments and simulation studies of bare land and gravel-sand mulched field with different planting years were conducted using combining theoretical analysis, numerical simulation and experimental research. This study illustrated the spatio-temporal patterns and transport regularity of soil water, heat and salt, revealed the transport mechanism of soil water, heat and salt. The parameters of crop root development, physiological ecology and yield under different irrigation systems were obtained. And the transfer model of soil water, heat and salt were built. The control irrigation indexes of soil water, heat and salt were further proposed based on water saving and salt control. These results will provide a theoretical basis for the sustainable development of agriculture in salinized area of northwestern China and further promote the popularization of gravel-sand mulched field.

压砂地是西北地区独特的旱作保护性耕作模式。土壤表层压砂会改变土壤地表形态和地面粗糙度进而影响土壤孔隙、减小土壤过水断面、增加孔隙弯曲度，使得土壤水热盐迁移过程比均质土壤更为复杂。随着种植年限的增加，砂石层演变为砂石土混合介质，这样对土壤结构、土壤物理性质以及水力参数均产生影响，进而影响土壤水热盐迁移机制，难以给决策者提供科学合理的解释和参考依据。为此，以压砂后农田土壤水分、热量、盐分的变化为出发点，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、不同种植年限压砂地进行定量实验和模拟对比研究，阐明压砂地土壤水热盐时空分布特征及迁移规律，揭示压砂地土壤水热盐耦合迁移机理，明确不同灌溉制度下作物根系发育、生理生态和产量等参数，构建压砂地土壤水热盐耦合迁移模型，提出基于节水控盐的土壤水热盐调控灌溉制度。为压砂地进一步推广及西北盐渍化地区农业可持续发展提供理论依据。

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，以压砂后农田土壤水分、热量、盐分的变化为出发点，采用理论分析、数值模拟及实验研究相结合的方法，开展了压砂地土壤水热盐耦合迁移机制及调控研究。通过室内实验，基于经典统计和地统计方法研究了压砂地土壤水分特征曲线参数的空间变异性，提出了一种利用土壤水分特征参数空间变化规律推断土壤水力特性的方法，指出Van Genuchten模型可以较好地模拟压砂地土壤水分特征曲线。通过野外大田实验，研究了压砂地不同种植年限和不同深度下土壤水分含量随时间的稳定性和变化规律，指出用代表性测点监测土壤水分含量是可行的；基于地统计学和克里格插值法，研究了砂石覆盖下枣园土壤水分、盐分的变异性，建立了土壤水分、盐分随深度变化的预测模型；通过数值模拟，基于反距离加权法和协同克里格研究了土壤盐分的空间变异性，指出反距离加权法可以较好地揭示土壤盐分的空间变异性。通过模拟实验，研究了土壤表面砂石覆盖条件下混掺0、0.1、0.2、0.5和1.0%浓度保水剂对土壤水分入渗的影响，率定出0.2%的效果最佳；研究了覆砂与无覆砂条件下添加0、0.1、0.2和0.5%保水剂对土壤水分入渗过程的影响，混掺0.5、1.5、2.5和4.5%生物炭对土壤水分入渗和蒸发的影响，建立了土壤水分入渗模型；通过数值模拟，研究了覆盖1、3、5、6、8、10、15和20cm厚度砂石对土壤水分蒸发和土壤温度的影响，率定出5cm的蓄水保温效果最佳。基于HYDRUS-2D模拟软件，在构建不同水土温度土壤水热运移数值模型的基础上，研究了滴灌条件下水温与土温对覆砂土壤水热运移规律的影响和不同灌溉水量、不同灌溉次数下土壤水盐、水热的变化规律，确定了压砂地适宜的节水控盐灌溉制度。项目研究成果已公开发表学术论文21篇，其中SCI/EI收录17篇；结合该项目研究，培养硕士研究生14名。