Using bulk density to calculate soil water changes in soils with shrinkage cracks

Abstract

Apparent bulk ña measured between shrinkage cracks is used to assess vertical shrinkage on the assumption that soil cores shrink isotropically from a fully swollen reference bulk density pr. A fully swollen depth increment ÄX corresponds to an increment Äx = (ñt/ña)1/3 ÄX at any other water content, field bulk density (which includes cracks) is given by and the fractional area of shrinkage cracks is 1 - (ñt/ña) 2/3. When gravimetric water contents are known, volumetric water contents can be calculated in terms of the fully swollen reference depth scale and changes in water contents of soil layers obtained. The procedure applies to any soil, from rigid through to one which undergoes normal shrinkage, provided the above assumption is satisfied. A BASIC program to perform the calculations is given.