Effect of Deficit Irrigation on Yield and Water Productivity of Seven Soybean Cultivars in Rasht Region

In order to evaluate the effects of deficit irrigation on yield and water productivity of seven soybean cultivars, an experiment was conducted as split plots based on randomized complete block design with three replications at agricultural research farm, Faculty of Agriculture, Guilan University. Main factors of the experiment were four irrigation levels based on soil moisture potential, 30-35 (I1, full irrigation), 50-55 (I2), 70-75 (I3) centibars (measured using tensiometer) and without irrigation (I4). Sub plot factors were included seven soybean cultivars: 033, 032, Sahar (maturity group IV), L.17, Zan, Clark and Madari (maturity group III). Water productivity was calculated based on seed and biological yield. The results showed that deficit irrigation significantly reduced seed yield. The highest and lowest values of the seed yield were obtained in I1 and I4, respectively. But irrigation water productivity significantly increased with application of deficit irrigation treatments (13% and 33% increment in I2 and I3, respectively). During the growing season, treatment I1 received the highest amount of irrigation (2457.14 m3/ha) and also the highest frequency of irrigations (8). According to the ratio of dry matter production to water consumption, water productivity of this treatment (I1) was low. Among all of the irrigation treatments, I3 showed the highest water productivity and there was no significant difference between I2 and I3 for the seed yield. It seemed that I3 had the best water productivity index. Among the studied cultivars, cultivar 033 showed the highest irrigation water productivity (this cultivar had the highest seed yield, as well). According to the results of the present experiment, in Rasht region, combination of treatment I3 and cultivar 033, not only economizes water consumption, increases irrigation efficiency and optimum use of water resources but also produces satisfactory soybean seed yield.