Evaluation of crusting susceptibility of some Japanese soils based on water permeability and morphology of crusts

Abstract

Crusting susceptibility of 19 soils collected from upland fields in Hokkaido, Kinki, and Shikoku districts was evaluated based on microscopic observations, morphological parameters using the thin section-image analyzing technique (Tanaka and Kyuma 1992: Soil Sci. Plant Nutr., 38, 369-373) and water permeability after subjecting the samples to simulated rainfall. The morphology of the soil surface after the simulated rainfall treatment was classified into four types: type A with less disintegrated aggregates, thus, less crusted; type B with a relatively dense band, so-called “washed-in layer” (McIntyre 1958: Soil Sci., 85, 185-189), composed of disintegrated small aggregates at a few millimeters below the surface; type C with densely compacted layer and a “seal skin” (Mclntyre 1958: Soil Sci., 85, 185-189) composed of disintegrated fine particles at the surface; type D with morphological features similar to those of type C but lacking a “seal skin.” Water permeability parameter, —log K value, showed a high correlation with aggregate instability, r=0.815** (n=19), in accordance with the morphological types of crust. Morphological parameter (Tt/APt ratio) was also correlated with the -log K value (r = 0.656**, n=19) and aggregate instability (r=0.517**, n=19). Among the parameters, the water permeability (-log K value) was considered to be a suitable and practical measure for determining the degree of crusting, and, therefore, for comparing the crusting susceptibility among the soils. Based on the -log K value, the potential crusting susceptibility of soils studied decreased in the following order: type C>type D≫type B>type A.

Key Words:

• aggregate stability
• crust
• crusting susceptibility
• morphological characteristics
• water permeability