Effect of growth stage based irrigation on soil water extraction and water use efficiency of spring safflower cultivars

The Ogallala Aquifer is depleting at faster rates, and jeopardizing the future sustainability of agriculture in the Southern High Plains. We hypothesize that adoption of drought tolerant crops such as safflower (Carthamus tinctorius L.) will sustain crop production in the region. However, information on water use of safflower is limited. A field study was conducted during 2013 and 2014 to monitor the soil water extraction patterns, water use efficiency (WUE) and oil productivity of spring safflower under deficit irrigation. Three safflower cultivars (PI8311, 99OL and Nutrisaff) having different growth habits and yield potentials were grown under four irrigation treatments [fully irrigated (FI), stress at vegetative stage (VS), stress at reproductive stage (RS) and dryland (DL)]. The soil water extraction was observed in all irrigation treatments or cultivars down to the depth of 1.6 m in both years; however, there was difference in water extraction at each depth. Safflower exposed to water stress extracted more soil water from the deeper depths. The maximum water was extracted from 1.0 to 1.6 m soil layer. The water extraction down to 1.6 m from planting to harvest was the highest in RS treatment while it was next to FI treatment in terms of evapotranspiration (ET) and oil yield. The higher WUE of RS treatment compared to FI and VS treatments suggest that RS treatment utilized the available water more efficiently. The cultivar 99OL showed higher WUE and oil yield. Thus, deficit irrigation at reproductive stage of safflower and adoption of 99OL cultivar can improve WUE and oil yield benefits under limited water conditions.