TIME OF SALT STRESS AFFECTS GROWTH AND YIELD COMPONENTS OF IRRIGATED WHEAT

Salt tolerance of wheat (Triticum aestivum L.) is known to change during different stages of growth. The effects of salinity on growth and yield components of wheat at different stages of growth were determined in a 2-yr field plot study at Brawley, CA. Four salinity levels were imposed on a Holtville silty clay [clayey over loamy, mont-morillonitic (calcareous), hyperthermic Typic Torrifluvent] by irrigating with waters salinized with NaCl and CaCl2 (1:1 w/w). Electrical conductivities of the irrigation waters were 1.4, 10.0, 20.0, and 30.0 dS m-1 in 1989, and 1.4, 8.0, 16.0, and 24.0 dS m-1 in 1990. The three irrigation treatments were (i) salinity imposed throughout the growing season, (ii) saline irrigation initiated after terminal spikelet differentiation (TSD), and (iii) saline irrigation discontinued at TSD. Growth and yield components measured were straw yield, total above ground biomass, number of spikelets per spike, number of kernels per spike, individual kernel weight, number of tillers per plant, and number of tiller spikes. Continuous salinity throughout the growing season significantly reduced all growth and yield components. Salinity imposed prior to TSD reduced the number of spikelets per spike and the number of tillers per plant, whereas salinity imposed after TSD significantly reduced only kernel number and weight. In general, the effect of salinity appears to be most pronounced on the yield components that are growing or developing at the time the salt stress is imposed. Total grain yields were maintained when moderately saline irrigation waters were substituted for good quality water during part of the growing season.