The significance of the threshold and turbidity concentrations in relation to sodicity and microstructure
The significance of the threshold and turbidity concentrations in relation to sodicity and microstructure
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DOI：
10.1071/sr00050
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发表时间：
2001-11
期刊：
影响因子：
1.6
通讯作者：
J. Quirk
中科院分区：
文献类型：
--
作者：
J. Quirk
Quirk和斯科菲尔德（1955）在他们关于电解质浓度对土壤渗透性的影响与碱度的关系的论文中指定了两个浓度：阈值浓度，它与对土壤结构的第一个可辨别的影响有关;以及浊度浓度，此时土壤微结构的解体表现为渗滤液中出现分散的颗粒，这发生在电解质浓度约为阈值浓度的四分之一时。这种行为解释的粘土领域，这是许多粘土颗粒在平行排列的组合。在粘土域中，存在表面间距约等于粘土晶体厚度的狭缝状孔隙。当钙是主要的可交换离子时，粘土结构域是稳定的，因为在相邻晶体重叠的地方，由于强吸引力，表面驻留在势阱中。这些吸引力类似于那些负责Camontament和Ca-蛭石晶体的稳定性。一个模型的3粘土晶体是用来说明如何在一个粘土域的晶体相互作用，在经典的排斥扩散双层力和现代的吸引力，影响域的稳定性。提请注意一个误解，现在流行的文献中，不承认浊度浓度相对于微观结构的基本意义，并错误地认为，所需的电解质浓度的影响分散到絮凝过渡在土壤悬浮液中可以用于预测所需的电解质水平，以维持土壤渗透性或渗透率在灌溉实践中。结果表明，絮凝剂的絮凝浓度几乎是浊度浓度的8倍。讨论了临界浓度概念在灌溉实践中的应用。它表明，阈值和浊度浓度舒适地解释了行为的重粘土进行边界检查灌溉和Cajon桑迪壤土在亚利桑那州。
Quirk and Schofield (1955) in their paper on the effect of electrolyte concentration on soil permeability in relation to sodicity designated 2 concentrations: the threshold concentration, which related to the first discernible effect on soil structure; and the turbidity concentration, at which the dismantling of the soil microstructure is indicated by the appearance of dispersed particles in the percolate—this occurs when the electrolyte concentration is about one-quarter of the threshold concentration. This behaviour is explained in terms of clay domains, which are assemblages of many clay particles in parallel alignment. Within a clay domain, slit-shaped pores with surface separations about equal to the thickness of clay crystals exist. When calcium is the dominant exchangeable ion the clay domains are stable because where contiguous crystals overlap the surfaces reside in a potential well as a result of strong attractive forces. These attractive forces are similar to those responsible for the stability of Camontmorillonite and Ca-vermiculite crystals. A model of 3 clay crystals is used to illustrate how crystal interaction within a clay domain, in terms of classical repulsive diffuse double-layer forces and modern attractive forces, affect domain stability. Attention is drawn to a misconception, now prevalent in the literature, which does not recognise the basic significance of the turbidity concentration with respect to microstructure and wrongly contends that the concentration of electrolyte required to effect the dispersion to flocculation transition in soil suspensions can be used for predicting the level of electrolyte required to sustain soil permeability or infiltration rate in irrigation practice. It is shown that the flocculation concentration is almost 8 times the turbidity concentration. The application of the threshold concentration concept in irrigation practice is discussed. It is demonstrated that the threshold and turbidity concentration comfortably explain the behaviour of a heavy clay soil subjected to border-check irrigation and Cajon sandy loam in Arizona.