Microtopographical Characteristics of Artificially Formed Crusts

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Abstract
The properties of artificially formed crusts have usually been studied on two widely different scales: (i) the whole crusted area on which infiltrability was measured and (ii) small samples of crust as used for scanning electron microscope (SEM) studies. A close inspection of some crusts revealed the presence of small mounds protruding from relatively smooth plains. The surface characteristics of artificially formed crusts of a Plinthustalf with two levels of exchangeable sodium percentage (ESP) were investigated on three different scales viz. (i) macro: the whole crusted area as used for bulk infiltration measurements (500 mm by 300 mm), (ii) intermediate: having the typical dimensions of mounds (8–10 mm in diam. where local permeabilities were determined), and (iii) micro: having the dimensions of samples used in SEM studies. Mounds and plains exhibited different permeabilitiees with the mounds maintaining higher values than the plains irrespective of the ESP of the soil. This was due to the structural differences between the two features. The mounds maintained a profile relatively similar to the profile of an uncrusted soil even though some loose clay particles were evident on the soil surface. Conversely, in the plains a dense layer of compacted particles was visible at the soil surface. The area occupied by the mounds decreased with an increase in cumulative rain and ESP. The trend of the weighted permeabilities obtained from the intermediate scale measurements corresponded to the observed trend in the bulk infiltration measurements.