棉花根系分布对微咸水膜下滴灌田间水盐运移影响机制及定量刻画

Mulched drip irrigation with brackish water has been widely used for the cotton production in arid areas, which strongly attributes to the great utilization potential of bracksih water in China. The influence of cotton root distribution on field soil water-salt movement must be considered in order to give full play to the advantage of mulched drip irrigation with brackish water, avoid soil salinization and its relevant series problems. However, it is hard to finely description of the temporal-spatial distribution of cotton root morphology under mulched drip irrigation with brackish water, the influence of the temporal-spatial distribution of root distribution on field soil water-salt movement in the numerical simulation study is inadequate consideration, the mechanism of the influence of cotton root distribution on field soil water-salt movement is not clear at present. This project will carry out mulched drip irrigated cotton field and pot experiments with brackish water in a typical arid area. In situ monitoring, sampling test and other methods are applied to finely measure the cotton root morphology distribution, soil water potential, soil salt, evaporation, transpiration, etc. for some prospects as follows: (i) to reveal the regulation of cotton root morphology distribution, soil water-salt distribution in the root zone and root water uptake during process growth of cotton root, (ii) to build cotton root growth model, and then embed into a program of soil water-salt movement numerical simulation to simulate the process growth of cotton root, root morphology distribution and its influence on field soil water-salt movement during cotton growth period, and (iii) to propose measures for optimize regulation of drip irrigated cotton field soil water-salt with brackish water. The research achievements could provide theoretical basis for using brackish water efficiently, prevention soil salinization and the sustainable development of agricultural in arid area.

我国微咸水利用潜力巨大，微咸水膜下滴灌已被广泛用于干旱区棉花生产。为充分发挥微咸水膜下滴灌优势，避免盐渍化及其衍生的系列问题，必须考虑棉花根系分布对田间水盐运移影响。但目前研究较难精细刻画微咸水膜下滴灌棉花根系形态时空分布，现有数值模拟对根系时空分布对田间水盐运移影响考虑不多，棉花根系分布对田间水盐运移影响机制尚不清楚。本项目拟在典型干旱区开展棉花微咸水膜下滴灌田间和盆栽试验，通过原位监测与采样测试等手段，精细监测棉花根系形态分布、土壤水势、含水量、盐分、蒸发、蒸腾等要素，揭示棉花根系生长过程中的形态分布、根区水盐分布及根系吸水规律。构建棉花根系生长模型，将其嵌入土壤水盐运移数值模拟程序仿真棉花生长期内的根系生长过程、形态分布及其对田间水盐运移影响，提出棉花微咸水滴灌田间水盐优化调控措施。其成果可为干旱区微咸水有效利用，防治土壤盐渍化，实现农业可持续发展提供理论依据。

我国微咸水利用潜力巨大，微咸水膜下滴灌已被广泛用于干旱区棉花生产。为充分发挥微咸水膜下滴灌优势，避免盐渍化及其衍生的系列问题，必须考虑棉花根系分布对田间水盐运移影响。但微咸水膜下滴灌棉花根系形态分布和土壤水盐相互作用关系复杂，现有数值模拟对根系时空分布对田间水盐运移影响考虑不多。本项目在系统剖析膜下滴灌棉田土-作物系统和水盐运移特征基础上，开展棉花微咸水膜下滴灌田间和盆栽试验，精细观测棉花根系形态分布、水盐均衡项要素，以及气象、农学等配套指标。获得了基于微根管原位动态监测膜下滴灌棉花三维根系空间分布，发现细根主要生长在0-45cm土层中，从苗期到花铃前期根长密度增加，花铃后期下降，平均根长密度在蕾期最高，扎根深度达107cm，平均根长增长率为1.55mm/d，平均存活天数为56天。揭示了不同覆膜滴灌模式下棉花根系生长过程中根系形态和土壤水盐热相互作用及其对地上部生长的影响规律，发现水分受根系吸水作用影响聚集于根系密集区附近，灌水后根区根系密度大的区域（深度15-32.5cm）水分下降而盐分聚集明显，微咸水灌溉处理根区过量盐分累积将抑制根系生长，进而导致棉花减产。利用溴示踪法、茎流计监测结合数值模拟评估了膜下滴灌棉田灌溉水入渗补给量及蒸腾量变化规律，膜下滴灌棉田地下水补给量仅占总降雨和灌溉量的0.8-5.6%，宽行处平均入渗补给系强度大于膜间，花期相较蕾期平均蒸腾量增长最快且晴天日蒸腾量大于阴天。建立了考虑棉花根系生长动态变化的膜下滴灌田间水盐运移数值模型，验证结果表明模型的误差在可接受范围，且该模型的误差指标优于传统的根系静态分布模型，分析揭示了根系分布动态变化影响下的田间水盐运移规律，表明考虑根系分布动态变化可提高根系生长在不同生育期差异较大土层水盐运移模拟精度。研究成果可为干旱区微咸水有效利用，防治土壤盐渍化，实现农业可持续发展提供理论依据。