Morphological characteristics of soil surface crusts formed under simulated rainfall

Open Access
Publisher Website
Google Scholar
Abstract
Morphological surface characteristics of soil samples, subjected to simulated rainfall with an intensity of 4.48 mm/min for different periods of time, were observed and quantified by applying the image analyzing technique to the binary image of the thin section specimens (TS-IA method). In the microscopic observation, two types of crust morphology were recognized; in one type, the crust consisted of a densely packed layer of finer particles with a “seal skin” (McIntyre 1958) of the uppermost surface, and in the other type, the crust consisted of a relatively dense layer of clogged smaller aggregates, designated as “washed-in layer” (McIntyre 1958), underlying the coarse aggregates and sand grains. Operationally, a “crust” is defined as a zone that extends continuously with a certain value of low apparent porosity (AP). By setting the critical value arbitrarily at 5%, in this study, the morphological characteristics of the soil crusts were quantified, in terms of the sum of the thickness of low AP zones (71) and weighted mean apparent porosity (APt). The ratio (APt/71) was also determined as an index of the crusting susceptibility among the soil samples. These quantified morphological parameters corresponded well to the observations, suggesting that they could indicate the degree of crusting and, thus, be used for the evaluation of the crusting susceptibility of soil samples. It was also suggested that the stability of aggregates exerts a considerable influence on the degree of crust development.