WATER MOVEMENT IN DRY SOILS

hysteresis that occurs in the micro-hydrological characteristics of a soil (conductivity and diffusivity) as functions of water content and water potential between sorption and desorption is examined for three soils (sand, loam, and clay) and sepiolite. These materials, all aggregated, are sufficiently dry that both the vapour and liquid components of water movement are important. any water content or water potential the vapour conductivity is always bigger when wetting than when drying though differences may be small. There is hysteresis in water (vapour+liquid) conductivity as a function of water content when vapour flow but not liquid flow is dominant. Conversely, there is hysteresis in water conductivity as a function of water potential when liquid flow but not vapour flow is dominant. Both forms of this hysteresis are small. Hysteresis in diffusivity as a function of both water content and water potential exists, but is complicated. Variations caused by hysteresis, though real, are likely to be negligible in practice, swamped by effects caused by changes in the soil environment (e.g. temperature) or by changes in soil management (e.g. structure).     

斥水土壤中水热运动模型的应用

作者运用所建立的斥水土壤中水热运动的数值模型，模拟分析了以下因素对沟中时苗床不分散失与温度的影响：（１）不同的沟垄尺寸；（２）湿润剂；（３）镇压；（４）沟垄的走向。以此为当地的耕种工程设计提供了依据。一般认为土壤斥性严重影响产量，但采用沟种后，表层的斥水土壤形成的不透不的垄能促进雨水渗入沟中，又能阻止水分的蒸发，降低沟中的温度，有利于种子发育出苗，从而使不利因素变化成有利条件。     

ADAPTING TO CLIMATE CHANGE BY IMPROVING WATER PRODUCTIVITY OF SOILS IN DRY AREAS

Considering extreme events of climate change and declining availability of appropriate quality water and/or highly productive soil resources for agriculture in dryland regions, the need to produce more food, forage and fibre will necessitate the effective utilization of marginal‐quality water and soil resources. Recent research and practices have demonstrated that effective utilization of these natural resources in dry areas can improve agricultural productivity per unit area and per unit water applied. This paper focuses on the following three case studies as examples: (1) low productivity soils affected by high levels of magnesium in soil solution and on the cation exchange complex; (2) degraded sandy soils under rainfed conditions characterized by low water‐holding capacity, organic matter and clay content and (3) abandoned irrigated soils with elevated levels of salts inhibiting growth of income generating crops. The results of these studies demonstrate that application of calcium‐supplying phosphogypsum to high‐magnesium soils, addition of clays to light textured degraded soils and phytoremediation of abandoned salt‐affected soils significantly improved productivity of these soils. Furthermore, under most circumstances, these interventions were economically viable, revealing that the efficient use of marginal‐quality water and soil resources has the potential to improve livelihoods amid growing populations in dry areas while reversing the natural resource degradation trend. However, considerably more investment and policy‐level interventions are needed to tackle soil degradation/remediation issues across both irrigated and dryland agricultural environments if the major challenge of producing enough food, forage and fibre is to be met. Copyright © 2011 John Wiley & Sons, Ltd.     

SPAC中的水分运动

本文对土壤-植物-大气连统体(SPAC)中水分运动的诸多方面,如非饱和土壤水分的导水参数,植物根系吸收土壤水分,植物根系中的水分运动.SPAC中的水流阻力及水容,土壤水分有效性动力学,滞后效应以及SPAC中水流的电模拟等.进行了介绍,评述和论述.     

不同质地土壤中铜离子运移阻滞因子研究

采用等温静态平衡吸附实验确定了重金属铜离子在3种不同质地土壤(砂质壤土,粉砂质粘土,壤质砂土)中的阻滞因子R,然后,结合混合置换实验中测定的铜离子和示踪剂离子的出流动态,采用了确定性平衡对流-弥散方程和确定性非平衡两区对流-弥散方程计算阻滞因子R。结果表明,Langmuir等温线形吸附方程可以准确描述铜离子的吸附特性;确定性平衡模型计算的R值与实测值接近;采用混合置换实验结合对流-弥散方程计算阻滞因子的方法耗时较长,精度不高。     

水肥状况对土壤剖面中锰的移动和水稻吸锰的影响

水旱轮作条件下水麦缺锰是四川冲积性水稻土上主要的养分胁迫问题,为了深入探讨这一问题,作者利用模拟土柱试验研究了不同水肥状况对四川两种典型冲积土中锰的迁移,转化及其对水稻吸锰的影响。     

COMPUTED EFFECTS OF ADSORPTION KINETICS ON PESTICIDE MOVEMENT IN SOILS

For a model at high water fluxes, the inclusion of first-order adsorption-desorption rate constants leads to slower leaching of pesticide and increased spread than predicted using instantaneous equilibrium. The initial condition of the substance near the soil surface is also found to be important. A model with simultaneous fast and slow adsorption-desorption equilibria describes and explains published experimental data comparatively well. Under a pattern of intermittent rainfall, the effect of adsorption-desorption kinetics on pesticide movement is comparatively small.     

一个冻土水盐热运动的数学模型

本文建立了一个冻土水盐热运动的数学模型。为了考虑土壤冻结和化冻时冰—液相变的影响,在传统土壤热传导方程中加入了溶化潜热运动项和存传统土壤水分运动方程中加入了相变项,从而推导出了三个相互关联的冻土水盐热运动方程,并提出了描述冻土未冻水含量随土壤冻结温度而变化的土壤冻结特征曲线及其实验测定方法。这个模型既可适应于冻土,也可适应于未冻土。     

粘性土壤剪切强度与容重和含水量之间关系的研究

本文在Mitchell等人关于土壤剪切强度唯一性研究的基础上,利用热力学第二定律作指导,由试验和分析建立了剪切强度与热扩散系数之间关系。据此关系,综合De Vries和佐滕用三相比表达热扩散系数的方程式,得到一个四参数剪切强度-干容重-含水量模型。对于一种粘土在各种容重和含水量下进行了三轴剪切试验,本模型拟合实测数据的精度(用相关系数表示)皆在0.9以上。     

CHARACTERIZATION OF WATER DISPLACEMENT IN SOILS USING SIMPLE CHROMATOGRAPHIC THEORY

Simple chromatographic equations were adapted to describe frontal water displacement by tracer-containing water in soils where only partial displacement occurs. The equations were shown to give excellent agreement with experimental data in five field experiments where tracer was added in artificial rainfall. The consequences of partial displacement for soil water replenishment in the root zone, salt leaching and ground water recharge are discussed.     

咸水灌溉沙地后的水盐运移规律

实地观测不同深度土壤含水率、基质势、土壤溶液含盐率 ,利用定位通量法和盐分均衡法 ,研究了咸水小畦灌条件下塔克拉玛干沙漠土壤的水盐运移规律。结果表明 :(1)在小畦灌条件下 ,停止灌水后 2 4h ,91.2 5 %的灌水渗入 15 0cm土层以下 ;停止灌水后 72h ,96.6%的灌水渗入 15 0cm土层以下 ,此时 ,0～ 15 0cm土层土壤平均含水率为 0 .0 5 3cm3cm- 3,此后土壤含水率缓慢下降。 (2 )秋季停灌后 ,土壤表面蒸发量在 2～ 6mm。停灌后 2h ,上行水区域在 0～ 2 0cm土层 ;停灌后 60h ,上行水区域在 0～ 90cm ;此后至停灌后 14 4h ,上行水深度稳定在地下 90cm。 (3 )咸水灌溉后 ,80cm以上土层土壤溶液含盐率明显下降 ,以下土壤溶液含盐率变化不明显。停灌 2 4h后 ,0～ 15 0cm土层液相盐分储量开始降低 ,至停灌后 14 4h ,0～ 15 0cm土层液相储盐量相当于灌水前的 5 3 .46%。 (4 )停止灌水后 ,10 0cm× 10 0cm地面日平均积盐量在 13～ 3 5g。     

斥水土壤中的水热运动规律与数值模型

斥水土壤很难被雨水湿润，影响种子发芽出苗而造成农业减产。由于地表干燥而引起风蚀水蚀，造成土地退化。这一问题在澳大利亚、荷兰、新西兰与美国引起重视。斥水土壤中水分分布往往是无规律的“指状”，到目前为止，没有成功的数学模型。作者从研究斥水土壤地区的耕作工程实践出发，采用沟种之后，水分的分布就有了规律性。开沟播种时，耕作机械把表层斥水性特别强的土壤推到垄上而形成几乎不透水的垄，下雨时雨水只能从沟中渗入形     

层状土中毛管水上升的实验研究

土壤盐渍化的重要机制是地下水中可溶盐在蒸发作用下不断向表土聚集;次生盐渍土的形成则可能是由于人为抬高地下水位,土壤毛管水重新分配土中盐分所致.不管怎样,防止土壤盐渍化的积极而彻底的方法是消除地下水位抬高的因素.但是,全面而根本的措施,往往限于客观条件不易做到,因此大多数都采取治标措施.例如,利用耕耘增加毛管水上升的困难,以及洪淤压碱等等.     

我国酸性硫酸盐土壤中铁锰形态转化及迁移

酸性硫酸盐土壤酸性很强，有机质含量高，造成了这种土壤所特有的铁锰淋洗、转化和迁移规律。研究结果表明：在酸性硫酸盐土壤中全铁含量较低，一般在３５－５０ｇ／ｋｇ（以Ｆｅ２Ｏ３计），全锰含量也低，一般在０．２５－０．５５ｇ／ｋｇ（以ＭｎＯ计），一般滩涂中全铁大于６０ｇ／ｋｇ，全锰大于１ｇ／ｋｇ。酸性硫酸盐土壤中，铁的游离度较小，一般在３７－７０％，铁的活化度较大，一般在８－２０％，而滩涂中铁的游离度一般     

EFFECTS OF CULTIVATION ON SOIL WATER RETENTION AND WATER USE BY CEREALS IN CLAY SOILS

The effects are repotted of direct drilling and mouldboard ploughing on soil water retention and extraction in three soils over two to four years. In the years 1972–75 when winter rainfall was close to or greater than the long-term average the maximum soil water content of the upper 100 cm differed little between the cultivation treatments. In contrast, after the dry winter of 1975–76, about 10 per cent more water was stored in the direct-drilled soil, especially below 50 cm. In the following dry summer, winter wheat extracted up to 22 mm more water from uncultivated soil and this was associated with better growth of the crop than after ploughing. When simulated rain was applied, water infiltrated rapidly to a depth of 50–100 cm in direct-drilled soil, whereas on ploughed land its movement was retarded below the plough sole even when cultivation had been carried out under conditions which minimized smearing. Water storage at depth was consequently greater under dry conditions in the direct-drilled soil while excess water reached drain depth more rapidly in wet conditions.     

黄土高原几种质地土壤的水分扩散率

本文采用水平土柱入渗法,测定了四种不同质地、不同孔隙度土壤的水分扩散率。结果表明,粘粒含量较多和孔隙度较小的土壤,单位时间内入渗水量较少,渗到既定距离需要的时间较长。各种质地土壤的扩散率D都随含水量增加而增加。当饱和度相同时,质地愈粘重,扩散率愈小。扩散率和孔隙度呈正相关。本文建立了土壤扩散率D和饱和度c的幂函数方程。将其运用到非饱和水分运动方程中,以有限差分数值计算法,所得土壤含水量的计算值和实测值比较接近,说明这些经验公式有一定的可靠性。     

粘土夹层土体构型水盐运动的实验研究

发育在冲积平原上的土壤,土体中夹有粘土层是很普通的现象。1987年在滨海平原110个土壤剖面调查中,发现粘土层以不同厚度和层位存在时,土壤表现出不同的盐渍状况,该地区粘土层表居很普遍。我们曾对粘土层在浅、中、深三个层位的5、15、30厘米三个厚度对水盐运动的影响作过研究,结果是枯土层对水盐运动的抑制作用随粘土层厚度 钓增加、层位的升高而加强^[2-5]。但是实际调查使我们感到有必要进一步研究土体中粘土层对水盐运动的影响规律,通过毛管水的上行运动的研究,了解粘土层的作用实质。     

非饱和土壤水分运动与热力学函数关系初探

在不同的温度条件下,研究了土壤水势对水分运动的影响,结果表明,在同一温度条件下,提高土壤水势可增加土壤非饱和导水率,呈现黄绵土＞lou土,在相同的土壤含水量条件下,增加温度可提高土壤非饱和导水率,其导水率温度效应值（dk/kt)lou土＞黄绵土。土壤含水量一定时,随着相对偏摩尔自由能亦[△（△-/G）]和相对偏摩尔焓变[△（△-/H）]增大,土壤非饱和导水率也增大,并且呈出黄绵土＞lou土,拟合得出的相对偏摩尔自由能变[△（△-/G）]和相对偏摩尔焓变[△（△-/H）]与土壤非饱和导水率方程,具有较好的适应性。