Water use efficiency of wheat in a Mediterranean-type environment. I. The relation between yield, water use and climate

The relations between wheat yield and water use were determined from field measurements in South Australia. Highest production of dry matter was 37 kg ha-1 per mm of water use and of grain was 12.7 kg ha-1 per mm. More than 70% of the total water use occurred by anthesis. Time of sowing and soil water content at sowing had a big influence on yield. The loss of water by direct evaporation was estimated to be 110 mm, equal to about one-third of the water use. The maximum efficiency of water transpired was 55 kg ha-1 mm-1 for dry matter and 20 kg ha-1 mm-1 for grain. The efficiencies of most of the crops were below this level. Yield (Y), water use (W) and evaporation (Ep) could be fitted to the de Wit formula Y = m W/Ep, but the m factor varied with the proportion of water use that was lost by direct evaporation.