Some aspects of soil shrinkage and the effect of cracking upon water entry into the soil.
Some aspects of soil shrinkage and the effect of cracking upon water entry into the soil.
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DOI：
10.1071/ar9540279
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发表时间：
1954
影响因子：
1.9
通讯作者：
G. Stirk
中科院分区：
文献类型：
--
作者：
G. Stirk
研究了伴随着取水而来的天然土壤团聚体的收缩情况。四个主要阶段的作用：(1)结构收缩，(2)正常收缩，(3)残留收缩，(4)无收缩：对于一定范围的土壤，测量了这些阶段运行的PF范围以及它们在总收缩中所占的比例。研究了组织和织构对收缩的影响。这些因素既影响收缩阶段，也影响收缩的范围。结构发展对收缩有显著影响，使收缩模式与淤泥或重塑土块的收缩模式截然不同。因此，建议用同一土壤的天然团聚体和淤泥砌块之间的孔隙度之差来评价土壤结构发育程度。为评价各种改进处理下的结构改善率提供了一个合适的指标。讨论了裂隙对提高细质土入水速率的影响。在灌溉土壤的特殊情况下，土壤水分含量保持在相对较高的水平(高于枯萎点)，似乎裂缝的发展可能不足以弥补这种土壤固有的低渗透性。在灌溉前耕种表层土壤以形成覆盖物，往往会消除土壤水分含量较高时出现的较小裂隙对传导的任何贡献。只有当水分含量降低到在连续灌溉栽培中不可行的水平时，由于土壤存在严重裂缝，渗透性才会大幅增加。
The shrinkage of natural soil aggregates that accompanies water withdrawal has been examined. Four main stages operate: (1) structural shrinkage, (2) normal shrinkage, (3) residual shrinkage, (4) no shrinkage: The pF ranges over which these stages operate and the fraction that they constitute of the total shrinkage has been measured for a range of soils. The influence of structure and texture upon shrinkage was assessed. These affect both the shrinkage phase and the range over which it operates. Structural development affects shrinkage markedly, giving a very different shrinkage pattern from that found for puddled soil or remoulded soil blocks. The difference in porosity between a natural aggregate and a puddled block of the same soil corresponding to a definite pF value is suggested, therefore, as a means of assessing the degree of structural development in the soil. It provides a suitable index for assessing the rate of structure improvement under various ameliorative treatments. The influence of cracking in increasing the rate of water entry into fine textured soils is discussed. In the particular cases of irrigated soils, where soil water contents are maintained at relatively high levels (above wilting point), it seems that cracking may not have progressed sufficiently to compensate for the low inherent permeability of such soils. Cultivation of the surface soil to form a mulch before irrigation tends to eliminate any contribution to conduction by the smaller cracks which are present at higher soil water contents. Large increases in permeability, due to the presence of gross soil cracks, are attained only when water contents are reduced to levels which are not practicable in continuous irrigation culture.