Laboratory simulation of the surface morphology of self-mulching and non-self-mulching vertisols .2. Quantification of visual features

Abstract

Descriptions of the surface morphology of Vertisols presently use subjectively classed, descriptive attributes. A system to quantify the appearance of the soil structural components is required to allow the comparison of soils, and to determine effects of variation in climate and of chemical/physical ameliorants. A non-destructive method of quantifying surface structural features is presented. Ponded and puddled samples of the 0-20 mm surface layer of a self-mulching Vertisol and two non self-mulching Vertisols were subjected to either a continuous drying regime or a sequence of wetting/drying cycles. Structural development with time was assessed by quantifying structural features using photographs of the soil surface. With repeated wetting and drying the self-mulching soil developed crumb material, the smallest shrinkage blocks, and the widest cracks. The non self-mulching soils developed no crumbs and the cracks generally became narrower. The range of structural development in terms of 'good' to 'bad' self-mulching in the laboratory agreed with the soils' behaviour in the field. Within the range of experiments performed, puddled soils did not produce as 'good' a self-mulching surface as non-puddled soils, no matter how many drying/wetting cycles were carried out.