Irrigation Management and Crop Modeling in Safflower.

The fast declining Ogallala Aquifer is a major challenge for the researchers to sustain crop productivity in the Southern High Plains. In addition, erratic droughts, heat waves, and low crop prizes are increasing the constraints for crop production in the region. Inclusion of low input, drought tolerant crops such as safflower (Carthamus tinctorius L.) is one of the strategies to extend the life of the Aquifer. A multi-year field study was conducted with the aim to assess the effects of preseason irrigation, in-season irrigation levels, and growth stage based deficit irrigation on stress physiology, yield formation, and water extraction patterns of spring safflower. A process based crop model, the CROPGRO, was also adapted for safflower to simulate its growth, seed yield, evapotranspiration (ET), and water use efficiency (WUE). In response to water stress, safflower used morphological modifications and stomatal regulation to maintain physiological activities. Reduction in leaf area index, light interception, photosynthesis, and plant biomass ultimately reduced seed yield under water stress. More water availability through preseason irrigation improved the seed yield of safflower compared to no-preseason irrigation, whereas no yield benefits were observed after a certain level of in-season irrigation level. Water extraction patterns indicated that safflower relied on soil moisture extraction when irrigation was not sufficient to meet its water requirement. Limiting irrigation after flowering was least detrimental to safflower yield and it was attributed to more efficient water use during this period. Overall, the CROPGRO-safflower model reasonably simulated crop phenology, growth, yield, ET, and WUE of safflower, however, further testing of the model under different environments is needed.