Readjusting the water balance to combat dryland salting in southern Australia: Changing the hydrology of a texture contrast soil by deep ripping

Abstract

Dryland salting is one of the biggest problems in dryland agriculture in southern Australia. It has been caused by the replacement of the original, deep-rooted, perennial trees and shrubs with shallow-rooted, annual crops and pastures. The accompanying decrease in evapotranspiration has caused an increase in deep infiltration to the groundwater. The rising groundwater has in many areas been salinised through mobilisation of salts previously stored in the regolith above the groundwater table. The effect on agriculture where such saline groundwater rises to or close to the surface is disastrous. To remedy the problem deep infiltration must be reduced again, preferably by increasing plant water use and at the same time increasing agricultural production. In this paper details are presented of a study in western Victoria of the relative effects of conventional tilling and deep ripping on water movement under, and yield of, phalaris and lucerne pastures on a texture contrast soil. Deep ripping reduced water logging and thus increased lucerne survival. Deep ripping increased penetrability to roots. It appeared to increase yield of both lucerne and phalaris significantly, and thus their water use. Deep ripping appeared, however, to decrease run-off and increase lateral flow to preferential flow channels leading downward; thus deep ripping appears to also increase deep infiltration. In addition it was observed that on this particular texture contrast soil the first major throttle to downward flow of water is not at the top of the B horizon but near the top of the C horizon. This would have considerable ramifications in terms of soil management.