Evaluating soybean response to water stress at different growth stages in Mazandaran province

In order to investigate the effect of water stress at different growing stages of soybean, an experiment was conducted in Mazandaran in a complete random block design with seven treatments and three replications. The treatments were consisted of: TR0 (no water stress), TR1 (water stress at vegetative stage), TR2 (water stress at flowering stage), TR3 (water stress at grin filling stage), TR4 (water stress at vegetative and flowering stage), TR5 (water stress at vegetative and grin filling stage) and TR6 (water stress at flowering and grin filling stage). The soil moisture was measured during the experiment by a gravimetric method, and hence, crop actual evapotranspiration was calculated by water balance method. The low rainfall amount did not disturb the treatments. After maturity, grin yield was measured, with yield response factor (Ky) being calculated for each growth stage and according to FAO method. The results indicated that the highest (5100 kg. ha-1) and lowest (2590 kg. ha-1) yield were obtained in TR0 and TR6 treatments, respectively. The largest seasonal evapotranspiration (36 mm) and the lowest (225mm) were belonged to TR1 and TR6, respectively. The yield response factor (Ky) was 0.87 for the total growth period and this factor at vegetative, flowering and grin filling stages were 0.148, 0.8 and 1, respectively.