Effects of flooding and subsequent drying on consolidation of beds of aggregates of a gray clay from Narrabri, NSW

Abstract

Changes in porosity of beds of aggragates of a grey clay, from Narrabri, NSW, on drying after flooding were studied in a laboratory experiment. For both surface soil (0-0.2m) and subsoil (0.8-1.0m) as a result of quick wetting, air-filled porosities sufficiently low (<0.1m3m-3) to be adversely affecting plant growth were recorded in the aggregate beds for much of the plant-available moisture range. Resultsindicated that, for the subsoil, the structural shrinkage phase was completely absent. Normal shrinkage prevailed and air-filled prosity remained at<0.1m3m-3 until the commencement of the residual shrinkage phase, which occurred at moisture content drier than the permanent wilting point (-1.5kj kg-1). Calcium chloride (0.01M) did not have an effect on the surface soil but significantly increased air-filled porosity of the subsoil by creating a structural shrinkage phase and hence reduced the extent of normal shrinkage (consolidation), Relevance of these laboratory results to field situations under furrow irrigation was discussed.