Water Use, Foliage Temperature and Yield of Irrigated Wheat in South-eastern Australia

Quantification of the relationship between evapotranspiration (Et) and yield is important for the analysis of irrigation practices. Wheat (Triticum aestivum cv. Avocet) was grown at the CSIRO Centre for Irrigation Research, Griffith, N.S.W., in 1982 with treatments of no irrigation and irrigation at 40, 70, and 90% depletion of plant available soil water. Irrigation significantly affected total dry matter, grain yield, and the yield components of number of heads per m2, number of grains per head, mass of individual grains, and harvest index. Plot grain yields, varying from 1.7 to 8.3 t ha-1, were closely related to dry matter at anthesis (r = 0.94) and number of grains per m2 (r = 0.99), indicating the importance of early growth on final yield. Regression analysis showed a significant (P < 0.01) linear relationship between Et and total or grain dry matter. The relationship of Et (mm) to grain yield (Y) (t ha-1) was described by Y = -2.010 + 0.016Et. Foliage temperatures were monitored at noon and showed promise as plant stress indicators. The mean differential between foliage and air temperature from jointing to late grain fill showed a strong negative linear relationship to grain numbers per unit soil area (r2 = 0.88) and to final yield (r2 = 0.86).