Deficit mulched drip irrigation improves yield, quality, and water use efficiency of watermelon in a desert oasis region

In the context of global warming, drought is a crucial factor affecting agricultural production, especially for the oasis farming areas of northwestern China, where water resources are extremely scarce. To reveal the response of watermelon water consumption (WC), yield, quality, and water use efficiency (WUE) to water deficit (WD) and to determine the optimal mode of irrigation in the desert oasis areas of Hexi, we applied different WD treatments on a field oasis watermelon in 2020 and 2021. The experiments employed two gradients of light (l) and moderate (m) WD treatments during the seedling (S), vine (V), expansion (E), and maturity (M) stages except for flowering and fruiting (F) stage, with full irrigation during the entire growth period as the control (CK). The results showed that the WC of oasis watermelon at each growth stage was in the order: E > V > S > M > F, in which WC by E stage accounted for 33.15-40.33%. Compared with the CK, WD had an obvious effect on water saving, and WD during the V or E stages inhibited the growth of vine leaves to a certain extent. The Sl treatment (light WD during S stage) had the highest yield and WUE, with significant increases of 5.23-5.38% and 7.10-7.37% (p < 0.05), respectively, in the two years, while the Mm treatment (moderate WD during the M stage) resulted in the best overall nutritional quality of watermelon, with soluble solids, soluble sugars, vitamin C, and soluble protein contents increasing by 11.31%, 33.43%, 24.03%, and 10.31% (p < 0.05), respectively. However, an integrated evaluation that coupled grey relation analysis (GRA) with a technique for determining order preference by its similarity to an ideal solution (TOPSIS) model, considering growth, yield, quality, and efficiency indicators, concluded that the Ml treatment (light WD during the M stage) achieved the highest comprehensive score, followed by the Sl treatment. Therefore, it is recommended that the optimal deficit irrigation mode for oasis watermelon is the Ml treatment, which can balance water savings, yields, and quality improvements, while the Sl treatment can be considered as a backup mode. This study provides theoretical and technical support for achieving efficient water-saving cultivation and scale development of watermelon production in desert oasis areas.