The effect of water stress in regulated deficit irrigation on soybean yield (Glycine max [L.] Merr.)

Abstract

The objective of this research was to investigate the effect of water stress in regulated deficit irrigation (RDI) on the yield of soybean growing on Ultisol soil. This research was conducted under plastic house on the experimental farm of Lampung Polytechnique from August to November 2004. The water stress treatments in regulated deficit irrigation were ET₁ (1.0 × ET_c), ET₂ (0.8 × ET_c), ET₃ (0.6 × ET_c), ET₄ (0.4 × ET_c) and ET₅ (0.2 × ET_c), arranged in a randomized block design with four replications. ET_c means crop evapotranspiration under standard condition, which was well watered. For example, the ET₂ (0.8 × ET_c) treatment means that the amount of supplied water per a day is the same as the crop adjustment evapotranspiration (ET_cadj) with the value 0.8 of water stress coefficient (K _s). The RDI treatments were carried out just at vegetative phase and its treatments were stopped at the beginning of flowering phase, and afterwards the treatments were watered at 1.0 × ET_c. The results showed that since week II, the soybean experienced stress throughout the growth period except ET₂ treatment. ET₂ treatment started to be stressed at week V and continued to be stressed until the harvest time. At the ET₃ treatment, the critical water content (θ_c) of soybean was reached at week II, and the θ_c was 0.24 m³/m³ on the average. The RDI at vegetative period significantly affected the yield. The highest yield was ET₁ (35.2 g/plant), followed by ET₂ (31.0 g/plant), ET₃ (18.1 g/plant), ET₄ (7.6 g/plant), and ET₅ (3.3 g/plant). The optimal water management of soybean with the highest yield efficiency was regulated deficit irrigation with water stress coefficient (K _s) of 0.80 for vegetative phase.