Influence of Water Stress and Pod Position on Oil and Protein Accumulation in Soybean Grains

A split-split plot experiment on the basis of randomized complete block design was carried out to investigate the effects of different irrigation treatments (I1, I2, I3 and I4: wellwatering on the bases of 70 mm evaporation from class A pan and irrigation disruptions at flowering, grain filling and during flowering and grain filling stages, respectively) in main plots on oil and protein content of three soybean cultivars (Clark, Williams and L17) in sub-plots at different pod positions (upper, lower and middle parts of the canopy) in sub-sub-plots. The results showed that with increasing water stress at reproductive stages protein percentage was increased, but oil percentage was decreased. Grain yield and protein and oil amounts per grain and yields per unit area were also decreased as a consequence of water limitation. Maximum oil and protein percentage were recorded for grains produced under I2 and I4, respectively. The superiority of Williams in protein amount per grain was mainly attributed to the production of larger grains by this cultivar. Grains of upper position of the canopies had high oil and protein content compared with those of middle and lower parts under all irrigation treatments.