Yield and water use relationships of potato under different timing and severity of water stress

Water scarcity is a prevailing problem that constrains crop production in many regions worldwide. The application of deficit irrigation strategy is a reliable approach, which may contribute to some degree to overcome the problem of global water scarcity. A two-year study was conducted to assess the effects of timing and severity of the deficit irrigation on yield, water productivity (WP) and yield response factor (Ky) of potato. In 2018, the treatments included: 100% (V100) of crop evapotranspiration (ET), 50% (V50–100) reduction of ET until end of tuber initiation, 50% (V100–50) reduction of ET during the middle of tuber bulking up to maturity stage and no irrigation following plant establishment (V0). In 2019, the treatments included: V100 and V0 as in the previous year, deficit irrigation at 50% of ET (DI50), partial root-zone drying (PRD) at 75 or 50% of ET applied during the whole growing season. Deficit irrigation at a reduced rate of 50% of ET crop during the first part of the crop cycle (V50–100) strongly depressed total yield while limiting irrigation water for the last part of the crop cycle (V100–50) did not induce significant losses in yield. Deficit irrigation positively affected water productivity, especially with V100–50, suggesting that water efficiency was closely related to the growth stage than to the available water in the soil. In 2019, reducing water to 75% of V100 with PRD75 did not significantly affect tuber yield, while the further reduction in the irrigation water with PRD50 or DI50 resulted in a substantial yield decrease. Although the same amount of water was applied to both treatments, the reduction in yield was 41% with DI50 compared to 28% with PRD50, where the latter proved to be superior in maintaining yield. However, an appreciable increment in WP was observed with both PRD treatments unless the water stress is too high to depress the yield. The sensitivity of potato to water stress was more remarkable when water was applied at individual growth stages than at different severities. In contrast, potatoes have been tolerant to both stress timing and severity in total dry matter. These results showed that using deficit irrigation late of the season or with PRD can improve water-saving, minimize yield losses, and consider optimal strategies for drip-irrigated potatoes in the arid regions.