optimization of single irrigation and sowing date for rainfed wheat varieties under dryland conditions

to investigate the effects of sowing date (sd) and single irrigation (si) on grain yield of rainfed wheat varieties, this experiment was conducted as split-split plot arranged in a randomized complete block design (rcbd) with three replications from sep.2000 to sep.2004 at the main station of dryland agricultural research institute (dari) in maragheh. the treatments included three sowing dates (early, customary and late), three levels of single irrigation (rainfed, 50mm and 100mm (only at planting time) along with five wheat varieties (v1(72yrrgp), v2(fenkang15/sefid), v3(turkey…), v4(azar2), v5(double cross shahi)). grain and straw yields as well as degree day index were studied for different sd and si treatments. the highest grain yield at si levels and rainfed conditions were for v3 and azar2 wheat varieties whilst grain yield of v1, v2 and v5 wheat varieties were less than those of the other varieties. the results indicated that 100mm single irrigation at early sd is indispensable while 50mm single irrigation sufficient at late sd. in general, based on interpolation method, optimum single irrigation program for rainfed wheat were recommended based upon 100 – 75 – 50mm water use at early, customary and late sd respectively. thus, when limited single irrigation is combined with appropriate management, wheat production can be substantially and consistently enhanced in these areas.