INFLUENCE OF WATER DEFICIT ON OIL AND PROTEIN ACCUMULATION IN SOYBEANGRAINS

A randomized complete block (RCB) design with three replications was arranged to evaluate soybean response to different irrigation treatments (I1, I2 and I3: irrigation after 70, 110 and 150 mm evaporation from A pan, respectively) in 2009. Sowing density was 64 seeds per square meter. All plots were irrigated immediately after sowing and irrigation treatments were applied after seedling establishment. The highest grain filling duration was recorded for plants under I1, followed by those under I3 and I2, respectively. However, grain filling rate under I2 and maximum grain weight under I3 were slightly higher than those under other irrigation treatments. High number of grains per plant under I2 resulted in production of smaller grains. Oil percentage of soybean under all irrigation treatments increased, but protein percentage decreased with proceeding of grain development. Water deficit caused a decrease in oil percentage and increase in protein percentage. Oil and protein yields per unit area had significant positive correlation with grain yield per unit area. Therefore, decreasing oil and protein yields per unit area under severe water stress was attributed to the large reductions in grain yield per unit area.