Combined effects of water-retaining agents and deficit irrigation on alfalfa resilience, irrigation water productivity, and economic returns

Water scarcity substantially limits sustainable alfalfa production in arid and semiarid regions. Water-retaining agents (WRAs) and deficit irrigation (DI) are effective strategies for improving crop yield and water productivity. However, the combined effects of WRAs and DI on physiological responses, water productivity and economic benefits in perennial crops remain unclear. This study investigated the combined effects of WRAs and DI on irrigation water productivity and economic benefits in alfalfa using a controlled pot experiment. Two WRAs levels (W0 and W1) and four DI levels (95 ± 5% (D0), 75 ± 5% (D1), 55 ± 5% (D2), 35 ± 5% (D3) of field water capacity) were applied. The results showed that WRAs application and DI enhanced photosynthetic performance and drought resistance, thereby increasing aboveground biomass, irrigation water productivity and net returns. The combined application of WRAs and DI increased leaf relative water content, maximum photochemical quantum yield (Fv/Fm), net photosynthetic rate (Pn), and irrigation water productivity. These combined effects account for a greater proportion of the variance in the measured traits than either factor alone. Structural equation model (SEM) further showed that WRAs and DI directly and indirectly influenced net returns through the regulation of chlorophyll fluorescence, water content, and aboveground biomass. Moreover, EWM-TOPSIS-AISM model identified W1D2 as the optimal water-saving strategy for maximizing irrigation water productivity and net returns under the controlled experimental conditions. These findings present a pattern of how the integration of WRAs and DI optimizing water productivity and net returns in perennial crops.