Effect of Various Soil Moisture Regimes on Grain Yield and Yield Components of Two Soybean Cultivars and Determination Their Best Drought Resistance Index

This experiment was conducted in the Research Farm of the Faculty of Agricultural Sciences, University of Guilan in 2010 as an RCBD based split plot experiment with three replications. In this experiment five different amounts of soil moisture (Irrigation after depletion of 45, 55, 65, 75 and 85% of field capacity moisture) and two soybean cultivars (Gorgan-3 and Williams) was considered as main and sub plots, respectively. Results of ANOVA showed that moisture regime by cultivar interaction had significant effect on seed yield, number of pods per plant, number of seeds per pod and seed oil percent. Mean comparisons revealed that increasing soil water depletion resulted to decrease in seed yield, number of pods per plant and number of seeds per pod. Also, it resulted to decrease in grain yield of both cultivars, which was approximately 63% for Gorgan 3 and 2% for Williams. However, maximum (1667kg/ha) and Minimum (384kg/ha) seed yield were recorded for Gorgan 3 and Williams in 45% and 65% soil moisture regimes, respectively. The highest seed oil percentage was recorded for cultivar Williams which grown in 75% soil moisture while the lowest was for Gorgan 3 which grown in 55 % soil moisture regime. Seed protein also was affected by soil moisture regime, significantly with the highest (22.49%) and lowest (22.04%) in 55 and 85% soil moisture regimes, respectively. In this experiment Williams had low sensitivity index and high tolerance index while Gorgan 3 had high geometric mean productivity and mean productivity. Overall, Gorgan 3 had the highest seed yield in all soil moisture regimes. Its yield reduction percent was greater in drought stress prone treatments, in comparison with cultivar Williams which shows greater seed yield stability of the indeterminate Williams cultivar