Response of groundnut to deficit irrigation during vegetative growth

Studies were conducted to investigate patterns of field water use efficiency (WUE) by groundnut under moisture stress. Experiment 1 examined four cultivars of Spanish groundnut (Arachis hypogaea L. ssp. fastigiata var. vulgaris), Ak 12-24, J 11, GAUG 1 and GG 2, during the summer seasons of 1989 and 1990. The crops were subjected to soil moisture deficit stress by withholding irrigation for 30 d, starting at 20 d after sowing (treatment T 101), and for 25 d starting at 20 d (T 102). In treatment T 101, the stress period was followed by two relief irrigations with an interval of 5 d. In Experiment 2, stress was imposed on cv. GG 2 from 10 to 30 d after sowing, based on an irrigation water/cumulative pan evaporation (IW/CPE) ratio of 0.6. In one case, this period of stress was followed with irrigation to maintain IW/CPE at 1.0 until harvest (T 200, control); in the second case, the initial stress period was followed by maintenance of IW/CPE at 0.8 until harvest (treatment T 201); in the third case, IW/CPE of 0.6 was continued until harvest (treatment T 202). The results of Experiment 1 showed that leaf area indices of plants stressed during the vegetative phase were higher during the reproductive phase, i.e. from 80 d after sowing until harvest, than those of control (T 100) plants. In general, percent dry matter distribution to leaves remained higher in control plants; percent dry matter distribution to the leaves of stressed plants was lower both during and after stress. Dry matter distributions to pods, and thus the harvest indices, were higher in the stressed plants. Among the treatments, total biomass and economic yields were higher in T 102, followed by T 101. The results of Experiment 2 were consistent with those of Experiment 1. Where groundnut is cultivated with irrigation, it is possible to increase field WUE and dry matter production, including economic yield, by imposing a transient deficit in soil moisture during the vegetative phase. (author)