Using Fuzzy Matter-element Model and Weighted Game Theory to Optimize Deficit Irrigation Scheduling for Sunflower.

[Objective] Sunflower is a cash crop grown in arid northwestern China. Improving its water use efficiency plays an important role in developing water-saving agriculture in that region. The aim of this paper is to find an optimal regulated and mulched deficit drip irrigation scheduling for it. [Method] The experiment was conducted in 2019-2020 in a sunflower field at Hexi Oasis. Water deficit was imposed at seedling and maturity stages, with soil water in other growing stages kept sufficient for roots to extract. Overall, there were six treatments, with the water deficit induced by keeping the soil water content at 75%~65% (mild), 65%~55% (moderate) and 55%~45% (severe) of the field capacity, respectively. The control was sufficient irrigation with the soil water content kept at 75%~85% of the field capacity. Each treatment had three replicas, which were designed using the completely random block experiment arrangement. The experimental results were analyzed using an improved fuzzy matter-element model coupled with the weighted game theory to quantify the effect of different water deficits on yield and quality, as well as water productivity of the crop. [Result] The effect of water deficit on the crop traits varied. A multi-level evaluation system revealed that in 2019, crop height had the highest weight (0.141) and the crude protein content had the least (0.083), while in 2020, crude fat content had the highest weight (0.162) and water use efficiency had the least (0.065). Comprehensive evaluation of the fuzzy matter-element model showed that the Euclidean degree was the best for a combination of mild or moderate water deficit at seedling stage and mild water deficit at maturity stage. [Conclusion] When water is sufficient, a mild regulated deficit irrigation (RDI) at the seedling stage coupled with a mild RDI at the maturity stage produces the highest seed yield, while when water is insufficient, a moderate RDI at the seedling stage combined with a mild RDI at the maturity stage works the best. The proposed model for optimizing regulated deficit irrigation is applicable not only for sunflower watered by mulched drip irrigation, but also for other crops irrigated by other methods. [ABSTRACT FROM AUTHOR]