干旱区膜下滴灌棉田非均质土壤水盐反应运移机制与模拟

Soil salinization is an important form of the soil degradation in the arid area, and it seriously threats the agricultural production and the ecological environment. Salt accumulation in soil is the result of natural conditions and human activities. It is affected by evaporation, structure of the soil and the water-soil chemical interaction. However, the back donation of the water-rock chemical interaction and its influence on the hydraulic parameters of soil, and their influence on the water flow and solution transport system in the soil have not been attracted enough attention, which affects the precision of the evaluation and prediction. This study is conducted in the Bazhou Irrigation Experiment Station located in the northern area of Tarim Basin. Through laboratory and field experiments with precisely monitoring, the influence of the salt accumulation on the soil hydraulic parameters including permeability, thermal conductivity, porosity and the soil water characteristic curve (SWRC) and the formation of the salt accumulation in the heterogeneous soil have been characterized quantitatively. Coupling the monitoring information of the soil moisture, salt, heat and stable isotopes (D and 18O), numerical simulation will be built which couples the water-rock interaction and the change of the soil hydraulic properties. The model can be used to explore the salt-water-heat migration regularity and the salt accumulation characteristics of the heterogeneous soil in the cotton field with drip irrigation under mulch. Furthermore, it is conducive to put forward reasonable measures to control the soil salinization. Further field experiment will be conducted to verify the modeling result, and modify the model. This study is significance to have a deeper understanding of the soil salinization formation characteristics and the theory of soil water and solution transport system, and also has important practical significance to the soil salinization prevention and ecological environment protection.

土壤盐渍化是干旱区土壤退化的重要形式，是农业生产和生态环境的严重威胁。土壤盐分的聚集是自然、人类共同作用的结果，受蒸发、介质结构、水岩化学作用等因素控制。但目前研究中对水-土化学作用及其对介质改变而引起土壤水盐流动系统的影响重视不够，影响了土壤盐分聚集的评价和预测精度。本项目以塔里木盆地北缘的巴州灌溉试验站为基地，通过室内外试验与精细监测，定量刻画土壤积盐对土壤渗透性、导热性、孔隙度、土壤水分特征曲线等参数的影响以及非均质土壤中盐分聚集的形态，结合土壤水、盐、热、氢氧稳定同位素等监测信息，构建耦合水岩反应及介质水力性质变化的土壤水盐热运移数值模拟模型，探究试验区内膜下滴灌棉田非均质土壤中水盐热运移规律与盐分聚集特征，提出合理的控盐措施并进行田间试验验证。该研究对于深入认识干旱区土壤盐渍化形成机制与土壤水盐运移系统理论具有重要的作用，对于土壤盐渍化防治和生态环境保护具有重要的实际意义。

土壤盐渍化是自然、人类活动共同作用的结果，受蒸发、土壤、水岩反应等因素控制。但目前土壤水盐运移预测中很少耦合盐分溶解沉淀及其对水力参数的影响，局限了土壤盐渍化的预测精度和防治措施的确定。本研究以天山南北两侧的玛纳斯河流域和孔雀河流域膜下滴灌棉田为研究对象，综合土壤含水量、水势、温度、电导率、同位素等信息探讨膜下滴灌棉田的土壤水流系统模式及其对水盐分布的控制；采用土柱试验、同位素、数值模拟等方法探讨蒸发作用下水盐运移过程中的盐分结晶积聚及其对土壤水力参数的影响；利用数值模拟探讨不同灌溉模式的水盐分布特征。.研究结果表明：干旱区膜下滴灌棉田中土壤水流系统可划分为浅层和深层水流系统，浅层系统受滴灌、膜间蒸发、根系吸水和宽行温度势驱动，水流方向变化频繁，深层系统以垂向运动为主，二者过渡带为积盐区；根系分布对浅层土壤水流系统盐分分布的控制作用显著。蒸发作用下水分上移散失过程中伴随着不同成分易溶盐的分异结晶沉淀。耦合溶解结晶的土壤水盐反应运移数值模拟很好地仿真了蒸发积盐过程，显著提高了盐分预测精度。粘性土夹层改变了土壤水流系统模式，降低了蒸发量，分别在土壤表层和粘土夹层表面形成积盐区；基于等效渗透系数和累积导水系数的含水岩组划分方法提高了层状介质模拟层划分的可靠性。室内外实验和同位素信息显示，土壤溶液浓度增加降低了土壤水分蒸发量；蒸发导致盐分沉淀改变了土壤孔隙形态、孔隙度和水力参数，使土壤蒸发量降低并趋于稳定，直至盐壳破裂，α和Ks是引起蒸发变化的敏感参数；SWCC实验结果显示Fredlund-Xing模型描述高盐度SWCC的模型更合理。利用3个土壤水力参数数据库，构建了不同SWCC模型数据库。不同灌溉方案的模拟对比显示合理的配置滴灌、根系和膜间的位置可以更好地节水控盐。项目成果对于深入认识干旱内陆盆地土壤盐碱化的形成机制、盐渍化预测、盐碱地防治和生态环境保护具有重要科学意义和应用价值。