河套灌区盐渍土秸秆隔层控盐机理研究

Hetao Irrigation District is the typical region of soil salinization development in China. Our preliminary study found that placing straw interlayer in the depth of 35-40cm has significant effect on reducing soil salinity in the cultivated layer and promoting crop growth. However, about the mechanism of soil salinity control by straw interlayer was not clear so far. Strengthening the monitoring and analysis of soil pore structure parameter in the location of straw interlayer may be the breakthrough for revealing the mechanism of its action. Based on the field micro-plot experiment in Inner Mongolia, the following two areas will be studied in this project: ①Through the advanced monitoring system of soil water and salt parameters combined with soil samples collection and laboratory analysis, the spatial and temporal distribution characteristics of soil water, salt, pH and salt ions in the treatments representing different amounts of straw interlayer under two salinity gradients will be dynamicly measured so as to determine the effect of straw interlayer on the soil water and salt transport. ② The soil pore structure parameters of straw interlayer location in different crop growth stages will be quantitatively analysed by CT scanning technique, the soil saturated conductivity and unsaturated conductivity parameters in the same position will also be measured in the laboratory, and then the relationship between these soil physical parameters of straw interlayer location and soil water and salt distribution in the soil profile will be analyzed to reveal the mechanism of straw interlaye controlling salinity. On this basis, the optimization model of straw interlayer for soil salinity control will be proposed. The results will provide scientific basis for a large area of saline land improvement by straw interlayer in Hetao Irrigation District and other regions with similar conditions.

河套灌区是我国土壤盐渍化发育的典型地区。本课题组前期研究发现在地表下35-40cm处埋设秸秆隔层具有明显耕层控盐效果，有效改善了作物生长状况。但目前对于秸秆隔层的控盐机理尚不清楚。加强秸秆隔层所处层次土壤孔隙结构参数的监测分析可能是揭示其控盐机理的突破口。为此，本研究拟采用田间微区定位试验从两方面开展研究：①利用先进的水盐参数连续测定系统，结合土壤样品采集分析，对不同盐分梯度下不同用量秸秆隔层处理剖面土壤水分、盐分时空分布特征、pH值以及盐分组成离子迁移变化进行动态监测，系统揭示秸秆隔层条件下土壤水盐运动规律。②运用CT等监测技术，对秸秆隔层所处层次土壤孔隙结构参数以及饱和与非饱和导水率等参数进行定量分析，并探明这些参数之间及其与剖面水盐分布的关系，阐明秸秆隔层的控盐机理，在此基础上，提出盐渍土秸秆隔层的优化模式。研究结果将为河套灌区和其它类似地区利用秸秆隔层大面积改良盐碱地提供科学依据。

针对河套灌区盐渍土壤秸秆隔层的控盐机理不清的问题，采用田间微区定位试验和室内土柱模拟实验的方法，结合CT扫描和图像处理技术，探讨了不同条件下秸秆隔层的水盐调控特征及其控盐机制，并开展了秸秆隔层的技术优化参数与配套技术田间试验研究。结果表明：不同形态秸秆隔层均降低了0-40cm土层盐分含量，原状5cm长秸秆与粉末状秸秆隔层处理对0-40cm土层抑盐效果最为显著，且原状5cm长秸秆盐分淋洗效率最高。在作物生育期内秸秆隔层显著降低根系分布层土壤溶液浓度和离子含量，用量越大抑制作用越强，但从作物生长角度，800kg/667m2用量秸秆隔层产量最高。CT扫描技术能精确量化孔隙大小、体积以及连通性等二值化参数。在入渗开始前与结束后，秸秆隔层内部孔隙分布密度均明显高于CK处理，且孔隙形态特征复杂。不同物理形态的玉米秸秆隔层均显著提高了40～45 cm隔层处总孔隙度，各处理中以秸秆粉末隔层总孔隙度最高，且在灌溉水入渗各阶段均是≤1 mm孔隙度最大，阻碍灌溉水入渗效果显著。5 cm段状秸秆隔层孔隙度随深度变化波动较大，导致其优先流现象最为明显，持续时间较长。秸秆隔层总孔隙度和≤1 mm孔隙度越高对阻碍灌溉水入渗效果越明显，> 1 mm孔隙会产生大孔隙流加速水分入渗，而在入渗结束后这种大孔隙的作用减弱，但≤1 mm孔隙度的阻渗作用依旧显著。秸秆深埋3年后，在不同土层中，秸秆深埋处理与翻耕对照处理0.1-0.5mm当量直径孔隙度均无显著性差异，其占总孔隙的比例最高，该部分孔隙度对水盐调控的影响较大，决定了秸秆深埋三年后在抑制返盐的效果减弱。随着年限的增加，盐分的淋洗和蒸发通量均随秸秆厚度的增加而增加，5cm秸秆层厚度更有利于盐碱地改良的综合开发利用。在当前春灌基础上减少10%灌水量结合秸秆隔层是兼顾控盐、节水和稳产的方案。形成了盐碱地根区增施磷以及在10-30cm土层有机培肥建立肥沃亚表层，强化秸秆隔层改土效果的配套技术。本研究为利用秸秆隔层改良盐碱地提供了科学依据。