evaluation of phenological stages and yield of soybean cultivars under deficit irrigation conditions in rasht region

in order to investigate effect of deficit irrigation on phenological stages and yield of soybean cultivars, an experiment was conducted as split plots based on randomized complete block design with three replications at agricultural research farm, university of guilan in 2009. main factor was included four irrigation levels based on potential moisture 30-35 (i1), 50-55 (i2), 70-75 (i3) centibar soil using tensiometer and without irrigation (i4) and sub plot factor was included seven soybean cultivars 033, 032, sahar (belong to group maturity 4), l.17, zan, clark and madari (belong to group maturity 3). to determine thermal requirement growth degree day system was used. thermal units required by daily weather statistics for planting to flowering, planting to poding, planting to seeding, planting to maturity, seed filling period and reproductive period, were determined. at harvest time, the following data were recorded: plant height, no. of seeds per plant, weight of seeds per plant, plant dry weight, seed and biological yields. planting to poding period and planting to seeding period increased with reduction in water available and water deficit delayed appearance of pods. water deficit decreased the yield components, significantly. cultivar had significant effect on the yield components and all of phenological stages. the highest seed yield produced from 033 cultivar. in general, the results showed that water deficit is capable by delays in the occurrence of phenological stages in time and decreasing yield components, reduce yield of soybean. the lowest time for appearance of pods and the highest yield was belonged to i1. according to results, it seems that application of irrigation based on i1, can improve growth and yield of soybean in rasht region.