土壤机械组成及容重对水分特征参数影响模拟试验研究――以黄土为例
节水中心2009届博士研究生李卓，在导师吴普特研究员、冯浩研究员的指导下，经过三年努力完成了滴灌灌水器水力特性及抗堵塞研究。
研究方向：水土资源高效利用
摘 要
针对我国北方部分地区干旱缺水与水土资源大量流失并存，土壤水分蓄渗能力退化，农业生产对天然降水的利用效率低下等现实情况，进行黄土蓄水过程影响机制模拟试验研究，探索土壤组成结构特征对土壤水分入渗――存蓄――蒸发连续过程的影响机制。通过人工配制不同机械组成土壤并设置不同容重梯度，研究了以粘粒含量为量化指标的机械组成与容重对土壤入渗、蓄水、蒸发性能的定量影响，并设计复合试验，分别界定了机械组成与容重对土壤蓄水影响的贡献率，为我国干旱地区农业生产天然降水就地高效利用及土壤扩蓄增容产品开发提供一定理论依据。论文得出以下主要结论：
1、土壤机械组成对土壤入渗能力有较大影响，入渗能力随土壤粘粒含量增加递减，土壤稳定入渗速率、90 min累积入渗量与其粘粒含量分别呈幂函数、指数函数负相关。
2、土壤机械组成对土壤蓄水能力有较大影响，土壤蓄水能力随粘粒含量增加而递增。试验土壤饱和含水量与粘粒含量呈指数函数正相关；田间持水量及凋萎系数在粘粒含量小于30.4%前与粘粒含量分别呈指数函数、幂函数正相关，粘粒含量大于30.4%后呈对数函数、指数函数正相关；有效水含量在粘粒含量小于35.8%之前随粘粒含量增加递增，大于35.8%以后，转为递减。
3、土壤蒸发可分为两个阶段，第一阶段，绝对蒸发强度与土壤机械组成无显著相关，相对蒸发强度随粘粒含量增加而递减；第二阶段，绝对与相对蒸发强度均随粘粒含量增加递增。有效水保持时间在土壤粘粒含量小于15%之前随粘粒含量增加有减少趋势，粘粒含量在15%～30%，则随粘粒含量增加递增，粘粒含量大于30%以后，又转为递减。
4、土壤容重对土壤入渗能力有较大影响，土壤入渗能力随容重增大递减，试验砂壤、中壤、粘壤稳定入渗速率与容重均呈对数负相关，砂壤120 min累积入渗量与容重呈幂函数负相关，中壤、粘壤则均呈线性负相关。
5、土壤容重对土壤水分蓄持能力有较大影响，土壤蓄水能力随容重增大递减，比水容量也随容重增大递减，土壤饱和含水量、毛管断裂含水量、田间持水量、凋萎系数、有效水含量、易效水含量、迟效水含量与容重分别呈幂函数、对数、指数、指数、指数、幂函数、对数关系。
6、蒸发第一阶段，绝对与相对蒸发强度均随容重增大递增，第二阶段则随容重增大递减，有效水保持时间随容重增大递增。
7、由水分入渗、水分蓄持、水分蒸发三个连续过程组成的土壤广义蓄水过程各环节受机械组成的影响大于受容重的影响。
总体上，经过本论文的研究，作者在广义土壤蓄水能力影响机制，特别是土壤本身组成结构对其影响的作用过程与机理方面得了一些成果，获得了部分土壤组成结构参数对土壤蓄水过程各环节影响作用的定量关系，进一步明晰了土壤组成结构对土壤蓄水过程影响作用机制，为天然降水高效利用及土壤扩蓄增容产品开发方向提供一定理论依据。
关键词：土壤机械组成；土壤容重；入渗能力；水分蓄持能力；蒸发能力
SIMULATED EXPERIMENT ON EFFECTS OF SOIL MECHANICAL COMPOSITION AND SOIL BULK DENSITY ON SOIL WATER CHARACTERISTIC PARAMETERS
――TAKE LOESS SOIL FOR EXAMPLE
ABSTRACT
Based on the problems of that drought and water shortage existence at the same time in the north partial area of our country, the decrease of the ability of soil infiltration and the low utilization of natural rain resource in agriculture production, we do the research on the mechanism of the process of soil water storage and quest the effect of soil constitution and structure on the process of the loess soil infiltration-storage-evaporation. By the different level of soil bulk density which was completed in artificial way, we research the measurable influence of the proportion of clay particles and the soil bulk density on the soil infiltration, storage and evaporation. Though designing compound experiments, and give the definition of the different contribution of the mechanism component and the soil bulk density. And this theory form our experiment provides some degree theoretic basis for the efficient utilization of the natural rain resource in the drought area and the development of the production of soil expansion. This thesis gives some conclusions as follows:
1. Soil mechanical composition has a great effect on soil infiltration capacity, the more clay contained in soil, the weaker infiltration capacity. The stable infiltration rate and 90-min cumulative infiltration have negative power and exponential function relationship with clay particle content.
2. Soil mechanical composition has a great effect on soil water-holding capacity. Soil water-holding capacity strengthened with the increase of clay particle content. The saturated water of experimental soils has exponential function relationship with clay content. Field moisture capacity and wilting coefficient have exponential and power function relationship with clay content when soil clay content less than 30.4%. And the rulaitionship transform to logarithmic and exponential function relationship when soil clay content more than 30.4%. Available water increased with the increase of clay content when soil clay content less than 35.8%, and it decreased after the clay content point.
3. The process of soil evaporation can divided into two stages. At the first stage, the absolute evaporation intensity has no significant correlation with soil mechanical composition, and the relative evaporation intensity weakened with the increase of clay content. At the second stage, two types of evaporating intensity both enhanced with the increase of clay content. Avalaible water holding time decreased with the increase of clay content when soil clay content less than 15%, and it increased when soil clay content between 15% and 30%. But after soil clay content more than 30%, it converted to decrease.
4. Soil bulk density has a great effect on soil infiltration capacity. Soil infiltration capacity weakened with the increase of its bulk density. The stable infiltration rate of sandy loam, medium loam and clay loam all have negative logarithmic function relationship with their bulk density. 120-min cumulative infiltration of sandy loam has negative power function relationship with its bulk density. For medium loam and clay loam is negative linear relationship.
5. Soil bulk density has a great effect on soil water holding capacity. Soil water holding capacity and specific water capacity both weakened with the increase of its bulk density. The saturated water content, field moisture capacity, wilting coefficient, available water, readily available water, slowly available water of experimented soils respectively has negative power, logarithmic, exponential, exponential, exponential, power, logarithmic relationship with soil bulk density.
6. Both absolute and relative evaporation intensity enhanced with the increase of bulk density at first evaporating stage and weakened at second stage. Avalaible water holding time increased with the increase of bulk density.
7. Experimental soil mechanical composition has more effects than bulk density on the generalized soil water holding process which involving three links of water infiltration, water holding and water evaporation.
In general, after the study of this thesis, the author made some success over the following aspects as generalized soil water storage capacity impact mechanism, particularly the action process and principle of the effects that the soil composition structure producing to itself, obtained partial quantitative relationship of the influential action that soil composition structure parameters producing to each links of soil water storage process, further clarified influential action mechanism that soil composition structure producing to soil water storage process, provided a theoretical basis for the efficient use of natural precipitation and the product development direction of soil storage capacity expansion.
KEY WORDS: soil mechanical composition, soil bulk density, infiltration capacity, water holding capacity, evaporating capacity