盐渍化农田水-热-盐传输过程与作物生长的特征及模拟

In China, the salinized croplands have become precious reserve soil resources. Moreover, the utilization efficiency of agricultural water and land resources is low. Under such circumstance, improving the utilization efficiency of water resources in salinized croplands is the direct approach to solve this problem. The evapotranspiration of salinized croplands and the formation process of crop yield are essentially the interactions among salinity migration process, water-energy transfer process and crop growth process. However, the water-thermal coupling mechanism under the salinity stress is still undefined. The project selects the Guanzhong Plain as the study area and conducts the eco-hydrological observations over salinized croplands. This paper studies the interactions among cropland evapotranspiration, energy transfer and crop physiological and ecological characteristics so as to reveal the inner mechanism of cropland evapotranspiration and propose a calculation method for cropland evapotranspiration under the salinity stress. Besides, this paper establishes the water and salt transfer model of salinized croplands and crop growth model under the salinity stress, builds the coupling model between water, energy and salt transfer process and crop growth, systematically analyzes the historical space pattern of water deprivation of salinized croplands and dynamic changes of soil salinity in root zone, and simulates the influences of salinity stress on the water deprivation and crop growth of salinized croplands under future climatic variation. The resulting conclusions can provide a scientific support for improving the utilization efficiency of agricultural water resources.

我国盐渍化农田已成为宝贵的后备土壤资源，提高盐渍化农田的水资源利用效率是解决农业水资源利用效率较低的直接途径。盐渍化农田蒸散发与作物产量的形成过程其实质是盐分运移过程、水热传输过程和作物生长过程的相互作用；然而，盐分胁迫下水-热耦合机理仍不明确。本项目以关中平原为研究区域，开展盐渍化农田生态水文观测和理论分析。通过观测，研究农田蒸散发与能量传输、作物生理生态特征的相互关系，以此揭示农田蒸散发的内在机理，提出盐分胁迫下的农田蒸散发计算方法；建立土壤水盐运移模型、盐分胁迫下作物生长模型，构建水-热-盐传输过程与作物生长的耦合模型，系统分析盐渍化农田耗水和根区土壤盐分动态变化的历史时空格局；模拟未来气候变化情景下盐分胁迫对农田耗水及作物生长的影响。为提高农业水资源利用效率提供科学支撑。

本项目以关中地区为研究区域，开展了盐渍化农田（冬小麦和夏玉米轮种制）生态水文观测，主要包括土壤含水量、土壤温度、土壤含盐量、蒸散发、降水、气温、风速等要素。通过整理观测资料，研究盐渍化农田常规气象要素变化和水盐运移规律。结果表明，降水呈现明显的季节波动和年际波动；相对湿度呈现先增长然后减小趋势。土壤含水量在20～110cm范围土层是接受外界水分补给并且水分运动较为活跃的区域；土壤电导率在110～180cm范围内保持较高水平；土壤温度在表层0～20cm范围内分布极值，这是因为表层土温最易受到对外界天气变化影响。通过搭建MIKE-SHE模型进行盐渍化农田蒸腾机理研究，通过反复调整模型参数，对模型的土壤分层进行了调整；最后进行模型验证，验证期模型效率系数Ens为0.74；决定系数R2为0.74；均方根平方误差为0.05。通过对模型模拟结果进行评价可知，模型较好的模拟了研究区的蒸散发。本文基于2013～2015年期间两个冬小麦-夏玉米轮作周期的试验数据资料来分别率定和验证模型。结果表明，经过率定和验证后的SWAP模型对研究区0～120cm各层土壤水热盐含量的模拟均保证了一定的精度，并较好地反映了各层水热盐含量的大致变化趋势，说明该模型能够进行研究区土壤水分、溶质运移以及热量传输的长系列预测，并且模拟得到的田间水盐平衡分量的计算结果是可靠的。最后，进行了农田冠层导度模型研究。根据观测资料，分析不同月份的干湿状态，然后计算冠层导度，分析冠层导度的变化特征；最后分析影响冠层导度的主要因素，建立干湿不同状态下冠层导度与影响因素的模型。结果表明，干湿状态下，所建模型在各个时段均存在差异。其中，在第一阶段，干态下温度的正作用小于湿态下的作用；在第二阶段，干态下水汽压亏缺的负作用小于湿态下的作用；在第三阶段，说明在此阶段干态下的水汽压亏缺的负作用小于湿态下的作用