Water productivity under deficit irrigation using onion as indicator crop

Improving water productivity (WP) through deficit irrigation is crucial in water-scarce areas. To practice deficit irrigation, the optimum level of water deficit that maximizes WP must be investigated. In this study, a field experiment was conducted to examine WP of the three treatments at available soil water depletion percentage (Pi) of 25% (reference), 45% and 65% using a drip irrigation system. Treatments were arranged in a randomized complete block design. The water deficit was allowed throughout the growth stages after transplanting except for the first 15 days of equal amounts of irrigations during the initial growth stage and 20 days enough spring season rainfall during bulb enlargement periods. Physical WP in terms of water use efficiency (WUE_f) for treatments T1, T2, and T3 was 9.44 kg∙m^-3, 11 kg∙m^-3 and 10.6 kg∙m^-3 for marketable yields. The WUE_f and economic water productivity were significantly improved by T2 and T3. The WUE_f difference between T2 and T3 was insignificant. However, T2 can be selected as an optimal irrigation level. Hence, deficit irrigation scheduling is an important approach for maximizing WP in areas where water is the main constraint for crop production. The planting dates should be scheduled such that the peak water requirement periods coincide with the rainy system.