effect of deficit irrigation at reproductive growth stages on growth and yield of four new sunflower cultivars

in order to study the effect of deficit irrigation at reproductive growth stages on growth and grain yield of four sunflower cultivars namely: azargol, allstare, alison and euroflor, an experiment was conducted during the 2007 growing season at the experimental field of the agricultural faculty of bu-ali sina university. the experimental design was a split plot one, based upon a randomized complete block arrangement with three replications. the irrigation levels included: full irrigation, deficit irrigation by withholding irrigation at heading, flowering, seed filling, at heading plus seed filling as well as at flowering plus seed filling stages. the indices of total dry weight accumulation (tdw), leaf area index (lai), crop growth rate (cgr), harvest index (hi), biological and economical yield (by and ey) were assessed. the results indicated that the highest lai (4.0), cgr (40.1 gm-2 d-1) and tdw (1537.9 g.pl-1) were obtained from euroflor cultivar when fully irrigated. euroflor had the highest of these values in deficit irrigation treatments. deficit irrigation in flowering stage had high decreasing growth indices especially in nar as well as in rgr and hi. euroflor cultivar and fully irrigated treatments exhibited the highest by (1012.7 and 1168.2 g.pl-1 respectively) as well as hi (40 and 42% respectively). the highest ey was obtained from intraction of euroflor cv. in full irrigation (500.8 g.pl-1) and euroflor cv. with deficit irrigation at seed filling stage. the same results were obtained for other cultivars in their fully irrigation treatments. the lowest ey belonged to azargol and alison in twice withholding irrigation at flowering and seed filling stages, and also in alison when twice withholding its irrigation at heading and seed filling stages. finally the treatments of twice withholding irrigation, and deficit irrigation at seed filling stage exhibit the highest and the lowest negative effect on growth and yield of sunflower respectively. euroflor cv. is finally suggested as a successful cultivar with the highest growth and productivity under various irrigation conditions.