INFILTRATION IN CRACKING CLAY SOILS AS AFFECTED BY INITIAL SOIL MOISTURE CONTENT

Infiltration of water in cracking clay soils is influenced by soil shrinkage as the soil moisture content decreases. The results of field experiments for two typical border irrigation cracking clay soils of southeast Australia showed that as the soil moisture content decreases the crack-fill increases and there is a non-linear relationship between crack-fill and soil moisture content. The relationship between coefficient of a two-term infiltration equation with constant exponent and soil moisture content was found to be linear. A general, two-term infiltration equation with constant exponent was developed which takes into account the changes of coefficient and crack-fill as they are affected by soil moisture content. There was a good agreement between prediction of this equation and field data. The results of the experiment for a wide range of soil moisture content changes showed that a third degree polynomial fits the data of soil surface subsidence, crack volume, and volume change vs soil water loss with high correlation coefficient. Soil surface subsidence and crack volume expressed in terms of unit area was found to be higher for field experiments compared to the laboratory experiments. The effect of crack volume on soil bulk density was found to be significant.