Growth and adaptation of soybean cultivars under water stress conditions .3. Yield response and dry matter production

Yield and dry matter production were examined under water-stress conditions. Two cultivars (Zhengzhuta 2 and Heinong 33) were grown in a concrete-framed field. From the flowering to the pod-filling stage, four levels of irrigation treatments were carried out (Treatment I, II, III and IV-from the severst, Treatment I to the non water stressed, Treatment IV). The growing periods were shorter with increasing amount of irrigation. Zhengzhuta 2 had larger shoot dry weight than Heinong 33 in every irrigation treatment. Dry weight of each organ tended to increase with increasing amount of irrigation during the treatment. Shoot dry weight ceased to increase in Treatment IV, but increased in the other treatments after the treatment. Percentage dry weight were higher in leaf and root of Zhengzhuta 2, and in pod of Heinong 33. Crop growth rates (CGRs), leaf area indices (LAIs), net assimilation rates (NARs) and pod growth rates (PGRs) were generally higher with increasing irrigation for both cultivars. CGR was closely related to LAI during the treatment. Pod, seed number and seed yield were greater in the plots with greater amount of irrigation. Zhengzhuta 2 had 5400 kg ha(-1) in Treatment IV. It's high-yielding potential seemed to be related to it's efficient leaf epansion and radiation interception ability.