Generation of microcracks in molded soils by rapid wetting

Abstract

Tillage of compacted or of puddled and remoulded soils is a major agronomic problem internationally. The natural regeneration of microcracks (tilth mellowing) prior to the cultivation of such soils can reduce the energy needed to work them. Rapid wetting, under certain conditions, plays a major role in developing cracks in structurally damaged soils. This study reports the use of different initial water contents and wetting rates to examine the development of 'new' soil structure, described mechanically by tensile strength, and optically by measurements of the relief of fractured soil surfaces. New terminology is introduced to describe the rate of wetting needed to induce mellowing and to describe the rugosity of soil fracture surfaces. Rapid wetting was found to induce microcracking in soils, even with initial matric potentials as wet as -1.0 to -1.5 MPa. Implications for water management are briefly considered. Visual and analytical evidence from photographs and computer images indicates that internal microcracking is almost always detectable whenever the wetting rate is sufficiently high to reduce the soil tensile strength.