Water entry, water use and seasonal-moisture regimes in flood-irrigated Riverina soils

Abstract

Soil water regimes were followed on a range of Riverina soils in field plots of subterranean clover, using a flood irrigation schedule typical for the Murrumbidgee Irrigation Areas. During winter, matric potentials remained high. During autumn and spring, potentials dropped rapidly on most soils after irrigation and the plants experienced considerable water stress and yields suffered. The rapidity of the drop in potential and the intensity of the subsequent water stress and depression of yield varied widely between soils. The variations in matric potential between soils may be explained in terms of the large differences in water-storage increment at irrigation. Mean increments ranged from 3.8 cm of water for a loam over clay profile to 12.5 cm for sandy-textured profiles. The range in water-storage increments was reflected in the water use of the plots, some of which lost water at barely half the potential evapotranspiration rate. For the period May 5 to October 23, the maximum water use was 44 cm compared with a Penman estimate of 38 cm for potential evapotranspiration. Water use and plant growth fell below the potential to the extent that water was not available because of low intake.