Monday, November 5, 2007 - 1:00 PM
61-1
The Dynamics of Soil Water Capture and Use: Experimental and Modelling Studies in Grain Crop Water Use Efficiency.
Graeme Hammer and Erik van Oosterom. The University of Queensland, Agricultural Production Systems Research Unit, School of Land, Crop and Food Sciences, Brisbane, QLD 4072, Australia
Crop water use efficiency (WUE), defined here as grain yield per mm of total water available to the crop, is determined by interacting factors operating at community and individual organism scales. At the community level WUE is affected by the proportion of the total available water that is captured as transpiration (T) and the seasonal distribution of that transpiration in the crop life cycle. At the organism level WUE is affected by the intrinsic plant transpiration efficiency (TE) and the nature of the atmospheric vapour pressure deficit (vpd). We have studied these underpinning factors in controlled and field experiments for contrasting elite hybrids of the C4 grass species, sorghum and maize and quantified and modelled the dynamics of root system development, canopy development, and timing and extent of water extraction. While we have found no differences in intrinsic TE, diurnal and seasonal patterns of vpd have some influence on realised WUE via effects on timing of T in the day and in the crop cycle. Differences in canopy development and the balance between root system and canopy development, however, generate the greatest effect on WUE by “shifting” water extraction and use from pre- to post-anthesis. In these situations the marginal effects of water use on grain yield are maximised, especially in terminal water-limited environments. Studies on the consequences of management (e.g. skip row planting configuration) and genetic (e.g. leaf size, tillering, root architecture) manipulations on WUE are presented and discussed.