【作者】 李明思；

【导师】 康绍忠；

【作者基本信息】 西北农林科技大学 ， 农业水土工程， 2006， 博士

【摘要】 膜下滴灌技术是滴灌技术与地膜栽培技术的结合,既有节水增产效果,也有增温保墒促使作物早熟的特点。虽然该技术在国内外多种经济作物上都有应用,但对其节水机理的研究并不深入,特别是关于该技术设计参数的研究成果很少,不利于该技术理论的发展。本文通过室内和小区试验以及大田生产实验,采用膜下滴灌、无膜滴灌和畦灌相比较的方法进行棉花种植,较为全面和系统地对滴灌系统设计中滴头流量选择问题、土壤湿润区(或湿润比)设计问题、线源滴灌土壤湿润均匀性问题、膜下滴灌土壤湿润区及土壤温度问题、膜下滴灌棉花根系分布及植株生长问题、膜下滴灌棉花产量和水分利用效率问题、盐化土壤膜下滴灌棉花土壤水、热、盐耦合和棉花生长特点等有关滴灌和膜下滴灌技术设计理论问题进行了试验、观测、分析和研究,得出了如下研究结论。(1)点源滴灌条件下,土壤湿润区形状本质上是受滴头流量与土壤入渗速度之间的相互关系影响。当滴头流量大于土壤入渗速度时,土壤表面出现积水区并向四周扩展,促使土壤湿润区水平运移速度增大,而垂直运移速度相应减小;当滴头流量小于土壤入渗速度时,土壤表面积水区很小或不出现积水区,湿润区垂直运移速度比水平运移速度快;当滴头流量不变而增加滴水量时,土壤入渗速度随时间而降低,其入渗速度逐渐小于滴头流量,土壤湿润区的水平运移速度加快。因此,滴灌技术设计中,应当以土壤设计湿润宽度作为滴头流量的设计依据,而在设计滴头流量时,应以土壤入渗特性和地表积水区变化过程作为计算基础。(2)线源滴灌土壤湿润均匀度影响着田间作物生长的均匀性,它是确定滴头间距的主要依据,同时也决定着线源滴灌滴头流量和滴水量的取值。沿滴灌毛管方向的土壤湿润均匀性取决于滴头下方土壤湿润区的交汇程度,交汇程度越大,土壤湿润均匀度就越大;垂直滴灌毛管方向的土壤湿润均匀性取决于滴头下方土壤湿润区的宽度,湿润宽度越大,湿润均匀度就越高;沿滴灌毛管方向的土壤湿润均匀度随滴头间距的减小而增大,随滴水量的增加而增加。(3)膜下滴灌条件下,地膜阻碍地表积水区向膜外扩展,使膜内土壤含水率远高于膜外土壤含水率,形成膜下整体灌溉的土壤湿润形式。所以,膜下滴灌的土壤设计湿润区就是地膜覆盖区。在行距30+60cm的栽培模式下,膜下滴灌的土壤湿润比为67%-83%,而无膜滴灌的土壤湿润比为33%-67%。膜下滴灌土壤灌水深度比无膜滴灌土壤灌水深度浅,比畦灌灌水深度更浅。膜下滴灌条件下,土壤含水率和土壤温度都比无膜滴灌条件下的土壤温度和含水率高。但是,土壤温度的变化主要受气候影响,只是在短期内受土壤含水率变化的影响。土壤温度的变化与土壤含水率的变化之间呈线性负相关。(4)膜下滴灌棉花总根量比无膜滴灌棉花总根量大,但比畦灌棉花总根量小。而且,膜下滴灌棉花根系主要分布在膜下土壤中,膜下滴灌毛管附近土壤中的棉花根重是膜外根重的14-23倍。膜边上的棉花根系的侧根大都偏向膜下土壤中生长。在垂直方向,膜下滴灌棉花根系比无膜滴灌棉花和畦灌棉花根系分布浅,0-30cm土层内的棉花根系重量占总根重的87%以上。其中,表层土壤中的棉花根重密度最大,而且根重密度随土层深度的增加呈指数函数递减。膜下滴灌土壤温度高,促使膜下滴灌棉花根系生长比无膜滴灌和畦灌棉花根系生长快,与后者相比,出现明显的早熟早衰现象。膜下滴灌棉花生育期进程比无膜滴灌和畦灌棉花的生育进程快,叶面积指数比后者的叶面积指数大,棉花早熟。(5)膜下滴灌棉花和无膜滴灌棉花的籽棉单产都比畦灌棉花籽棉单产增产40%以上。膜下滴灌棉花土壤耗水主要集中在膜下0-60cm土层内,膜内土壤耗水量是膜外土壤耗水量的7倍,而且土壤表层的耗水强度最大。膜下滴灌土壤耗水量随深度的变化与棉花根密度分布有关,它们之间的关系可用指数函数描述。膜下滴灌的棵间蒸发量仅仅是其植株蒸腾量的28.57%,是畦灌棉花棵间蒸发量的17.39%。膜下滴灌棉花的水分利用效率为1.332kg/m3,比无膜滴灌棉花高0.168kg/m3。膜下滴灌棉花灌溉生产率为1.304kg/m3,比无膜滴灌棉花高0.201kg/m3。理论上膜下滴灌棉花每kg籽棉耗水比无膜滴灌棉花节水15.4%。(6)盐化土壤上进行膜下滴灌时,土壤盐分呈环状分布,膜外或膜下深层土壤含盐率高,而膜内上层土壤含盐率低。此时,土壤湿润区越大对作物生长越有利,所以盐化土壤上进行膜下滴灌时土壤湿润比和湿润深度比非盐化土壤的同类指标大。重盐化土壤上膜下滴灌棉花受盐分胁迫严重,棉花生长期比正常情况下缩短15d;株高仅为正常生长棉花株高的一半,叶片过早衰亡,棉花产量低,品质差。另外,膜下滴灌条件下,盐化土壤因含水率和矿物质含量高,其温度比非盐化土壤温度稳定,受大气温度的影响不明显。盐化土壤膜下滴灌棉花根系分布呈现去盐性特征。棉花根系向含盐率较低的土层中生长,所以,棉花根系主要生长在土层上部,总根量小。更多还原

【Abstract】 The technique of drip irrigation with plastic film mulch, or called the mulched drip irrigation (MDI) is a combination of drip irrigation (DI) and plasticulture techniques, which is characterized by irrigational water saving, crop being premature and its output increasing, soil temperature increasing, and preservation of soil moisture. This irrigation technique has been used for many kinds of economic value crops over the world, but the water-saving mechanism for the MDI has not been studied thoroughly, especially the research result on the designed parameters for the irrigation technique is so little that is unavailable to the technique development. Experiments had been carried out in laboratory, plot of land, and field, to plant cotton with the irrigation techniques of MDI, DI, and border irrigation (BI) to systematically and comprehensively study the problems about the principle of designing the DI and MDI systems, such as, the design of dripper discharge for DI system, percentage of soil wetted area, soil moisture uniformity for linear source drip irrigation, soil wetting pattern and soil temperature for MDI, cotton growth and its root system distribution in soil with MDI, cotton yield and water use efficiency under MDI, the coupling of soil water and temperature with soil salinity under MDI, cotton growth in the saline land with MDI, and so on. By testing, observing, analyzing, and studying these problems, the results are obtained as follow.(1) With the point source drip irrigation, soil wetting pattern is influenced by the relation between dripper discharge and soil infiltration intensity. When dripper discharge is larger than soil infiltration intensity, a saturated pond occurs on the soil surface and expands around, then soil wetting front moves quickly in horizontal and slowly in vertical. But when dripper discharge is less than the soil infiltration intensity, the horizontal movement velocity of the soil wetting front would be slower than its vertical one due to no saturated pond occurring on soil surface. When dripper discharge is constant but dripping water is increased, the soil infiltration intensity would lessen with time and eventually be less than the dripper discharge and soil wetting front would move quickly in horizontal. Therefore, the width of soil wetting pattern should be the basis to design the dripper discharge for the DI system, while the soil infiltration and the dynamics of soil saturated pond are the foundation to calculate the dripper discharge.(2) Soil moisture uniformity is essential to determine the drippers spacing as well as the dripper discharge and dripping water for linear source drip irrigation system, and it influences the uniformity of crops growing in field. The soil moisture uniformity along the drip line depends on the overlap of soil wetting patterns beneath drippers, and the more the soil wetting pattern overlap, the higher the soil moisture uniformity is. The soil moisture uniformity across the drip line is subject to the width of soil wetting pattern, and the larger the soil wetting width, the higher the soil moisture uniformity. The soil moisture uniformity along drip line is improved by short drippers spacing and large dripping water.(3) With the MDI, the fact that soil saturation pond is limited by plastic film to expand around, results in that soil water content beneath film is far more higher than that outside of the film, and the soil beneath the film is wetted in border strip. So the designed soil wetting area for the MDI is just the soil surface area covered by the film. With plant row spacing of 30+60cm, the percentage of soil wetted area is 67%-83% for MDI, while 33%-67% for DI. The soil infiltration depth of MDI is shallower than that of DI or BI. Under the MDI, soil water content and soil temperature are lager than that under DI. Soil temperature is affected mostly by climatic conditions but by soil moisture conditions only in certain period although soil temperature varies with soil water content in negative-linear function.(4) With the MDI, the cotton root system distributed in the soil beneath drip line and the film is 14-23 times as weight as that distributed in the soil out of the film, and the lateral root of cotton which grows near by the sides of film distributes chiefly in the soil mulched by the film. So the total weight of cotton root under the MDI, which distributes mainly in the soil mulched by plastic film, is larger than that under the DI, but is less than that under the BI. But under the MDI, cotton root weight in the 0-30cm soil layer accounts for 87% of the total root weight, and it decreases exponentially with soil depth increasing although it is the largest in top soil layer. Therefore, the cotton root system irrigated with the MDI distributes shallowly comparing with that irrigated with the DI or BI. Cotton root under the MDI, by which soil temperature is high, grows quickly than that under the DI or BI, but it is obviously early ageing.Comparing with the cotton irrigated with the DI or BI, the cotton irrigated with the MDI grows quickly and its leaves area index is larger, so that it is premature but early ageing.(5) The per unit area yield of unginned cotton under MDI and DI is 40% higher than that under BI. Under the MDI, cotton consumes soil water mainly in 0-60cm soil layer where is covered by plastic film, and the water consumption in the soil layer is 7 times as high as it is in the soil out of the film; and of this soil layer, the top layer has the largest water consumption density. The function of soil water consumption with soil depth under the MDI is relative to the distribution of cotton root system density, and the relation of soil water consumption in soil depth and cotton root system density can be expressed exponentially. The evaporation from soil under MDI is only 28.57% of crop transpiration and is 17.39% of evaporation from the soil under BI.Water use efficiency of cotton under MDI is 1.332kg/m3, which is higher than that under DI by 0.168kg/m3. The production efficiency of irrigation water for the cotton irrigated with MDI is 1.304kg/m3, which is higher than that with DI by 0.201kg/m3. Theoretically, the water consumption of per kilogram unginned cotton under the MDI is 15.4% less than that under DI.(6) When saline soil is irrigated with the MDI, the salinity of soil is distributed in ring-like that soil salinity content is higher in the soil out of film and in deep soil, and is lower in the top soil layer beneath the film. The larger the soil wetting pattern, the more beneficial to crop growing the condition is. Thus the percentage of soil wetted area and soil wetted depth for saline soil is larger than that for un-saline soil. With MDI, the cotton growing on heavy salt soil will be saline stress, so that cotton growing period will be 15 days shorter than that growing normally, the cotton stem is only half of that growing normally, the cotton leaves are early ageing, and cotton yield is low as well as its quality is poor. In addition, the salt soil temperature is usually constant and doesn’t vary with climatic conditions comparing with the un-salt soil, because the salt soil is high water content and mineral. In the salt soil under MDI, cotton root system distribution is characterized by evading salt that cotton root grows in the soil of low salt content. So cotton root mainly distributes in top soil layer, and total root weight is little.更多还原