Response of Alternative Oilseed Crops to Deficit Irrigation in West Texas.

In regions where agricultural water is limited, growing alternative crops under deficit irrigation may improve water productivity and farmer profitability. Plants adapt to environments with low water availability through different physiological responses. In this study, the physiological response of cotton and alternative oilseed crops (safflower, sesame, and sunflower) grown under four different levels of deficit irrigation (DI: extreme - 51 mm, severe - 127 mm, moderate - 203 mm and mild- 279 mm) were compared. Sesame showed no significant difference in leaf water potential (ψ) under different DI, but for the other crops, extreme and severe DI treatments showed lower ψ compared to moderate and mild DI treatments. The decrease in ψ for these treatments may have reduced leaf expansion and encouraged stomatal closure as adaptive responses to less irrigation, as shown by decrease in specific leaf area and stomatal conductance at reproductive stage. Crops under low irrigation levels exhibited significantly lower leaf area index but comparable biomass to higher irrigation treatments. Number of heads per plant and seeds per head did not vary among treatments. Results showed no significant crop-by-irrigation interactions for yield and harvest index (HI). For all crops, yields were not significantly different among treatments. The HI of crops grown under severe DI treatment was comparable to extreme and moderate DI and was significantly higher than mild DI. For cotton and sesame, mild DI treatment had the lowest water use efficiency (WUE). Safflower had the highest WUE under moderate DI, which was comparable to extreme and severe DI treatments. Sunflower had the highest WUE under extreme DI treatment. These results indicated that these crops responded to water stress by allocating resources to early flowering and fruit production, and additional in-season irrigation after a certain level does not warrant any extra benefit to crop productivity and WUE.