Water balance of three irrigated crops on fine-textured soils of the Riverine Plain

Abstract

Three summer crop species, maize, sorghum and sunflower were grown on three different fine-textured soils of the Riverine Plain in south-eastern Australia. At each site, above-ground growth, phenological development, and root length density were measured in two well-watered plots. Water use, plant water status and final crop yield were measured in the well-watered plots and in one plot per site where irrigation was discontinued around the time that complete crop canopies had developed. Plant available water was estimated from these drying-cycle plots. Crop water use calculated from soil water contents did not agree with estimates from a water balance model at two of the sites, suggesting that capillary rise from shallow water tables was supplying considerable quantities of water to the crops. Using the water balance model to predict actual evapotranspiration (Et), we estimated that after complete canopy development, up to 40% of Et was supplied to well-watered crops from a water table at approximately 1.5 m. At the site without a water table, yields from the drying-cycle plots were severely reduced and the estimate of plant available water (PAW) was thought to be realistic. It was concluded that where capillary rise or lateral movement of water into the root zone was significant, the concept of plant available water (PAW) was unsatisfactory.