Relationships between fabric, water retention, and strength of hard subsoils in the south of Western Australia

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Authors: G.A. Kew, R.J. Gilkes and D. Evans
Date: Mar. 2010
From: Australian Journal of Soil Research(Vol. 48, Issue 2)
Publisher: CSIRO Publishing
Document Type: Report
Length: 4,165 words

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Abstract :

Crop yield in the sandy soils of the Western Australian wheatbelt is influenced strongly by the plant-available water (PAW) and strength of subsoils. The fabric of hard subsoils of fluvial and aeolian origin has been compared with that of in situ saprolite materials that also occur as subsoils in Western Australia. A fabric classification was developed and relationships between, fabric, water retention, and strength were examined. The clay matrix of hard subsoils is denser and is less porous than in saprolite. Hard subsoils contain rounded quartz grains and transported, rounded aggregates of clay (spherites), while saprolite contains angular quartz grains in a more porous isotropic kaolin clay matrix developed by in situ weathering. At all matric potentials there were large differences in water retention between hard subsoils and saprolite. The dry and wet strengths of subsoils are lower than for saprolite but the strength of both materials is similarly affected by changes in water content and matric potential. A variety of factors including the size, shape, degree of sorting of quartz grains, distribution of dense clay matrix, and cementing by iron oxides or amorphous silica affect the strength of subsoils. The fabric classification is predictive of water retention and strength. Additional keywords: compaction, grain size, quartz grains, clay matrix, unconfined compression strength, water retention, spherites, electron microprobe analysis, scanning electron microscopy.

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Gale Document Number: GALE|A225247437