干湿交替灌溉模式下灌淤土裂隙特征及其对优先流的影响

Soil structure changes along with alternate flooding and drying. The obvious characteristic is soil shrinkage will occur when it is drying, causing cracks in the field. The occurrence of soil crack is a complex process, which may be has some relationship with soil minerals, soil water evaporation, crop transpiration, soil water movement and soil tillage and field management and so on. Soil cracks can be used as the pathways of preferential flow, improving water infiltration, reducing water use efficiency and increasing the pollution risk of ground water. Thus, the project focuses on the anthropogenic-alluvial soil in Hetao Yellow River Irrigation District in Ningxia. By using outside investigation combined with experiment in laboratory and field, identify soil mechanical composition and quantified the soil structure, porosity, pore diameter and its connectivity by using CT scanning and image processing technology. First, by using indoor simulation experiment to study the effect of intensity and frequency of wetting and drying on soil shrinkage behavior; And the change of soil shrinkage capacity along soil depth. Second, the influences of rice growing on soil cracks and the temporal changes of soil cracks during period of rice growth will be recorded by using digital camera; and 3-D structure of soil cracks will be scanned by CT scanning. The characteristics of 2D and 3D soil cracks will be quantified with the aid of image analysis. Third, the influence of soil cracks on preferential flow will be characterized by tension infiltrometer, dye tracer and ion breakthrough curve. Finally, the water balance and water use efficiency under alternate flooding and drying irrigation method will be evaluated. Those results will provide some measurements for mitigating soil and water loss and soil cracks，increasing water and fertilizer use efficiency，decreasing the pollution risk of groundwater，supplying academic support for making reasonable irrigation technological parameters such as rational irrigation frequency and intensity， and offering practical direction for water saving agriculture.

土壤结构随干湿交替而变化，最明显的特征是土壤遇到干旱后产生裂隙。裂隙产生会作为优先流的路径，加速稻田水分和养分的损失，降低了水分利用效率，同时也增加了地下水污染的风险。如何动态描述土壤裂隙的几何形态是研究土壤裂隙特征和优先流的关键。本项目以宁夏河套平原引黄灌区灌淤土为研究对象，通过野外原位监测裂隙动态变化与土壤水分/水势揭示两者的耦合关系；采用田间拍照和X射线CT扫描成像技术分别分析土壤裂隙的二维和三维的空间特征；通过室内土柱模拟实验阐明干湿交替强度和次数对裂隙产生驱动机制及其影响因素；并通过田间染色示踪、圆盘入渗和溶质穿透曲线相结合定量评价裂隙变化对优先流的贡献及水分利用效率的影响, 为提高灌区水肥利用效率、提出防止和减缓裂隙产生的措施、降低地下水污染、制定合理农田灌溉技术参数、确定适宜的灌溉次数和强度和发展节水农业提供理论依据和实践指导。

土壤结构随干湿交替而变化，最明显的特征是土壤遇到干旱产生裂隙。已有结果表明裂隙在土壤优先流、溶质运移和环境污染物的迁移方面具有重要作用。研究裂隙对农田灌溉、水肥利用以及地下水污染等方面有重要的科学和实践意义。本项目在调查研究河套灌区灌淤土分布区土壤裂隙产生机制及其影响因素的基础上，通过直接与间接的实验方法研究干湿交替灌溉模式对裂隙产生的影响。采用CT扫描、染色示踪、圆盘入渗、穿透曲线等技术手段，建立裂隙三维形态特征的图像分析方法，分别分析不同干湿强度和次数下裂隙动态变化及对土壤裂隙稳定性的影响，以及裂隙三维结构特征对土壤结构和优势流的影响。本项目的研究可以提升裂隙及其功能的认识，为农业生产和环境治理提供科学依据。