Using the CROPGRO Model for Predicting Water Balance, Evapotranspiration and Water Use Efficiency of Spring Safflower.

Safflower (Carthamus tinctorius L.) is a drought tolerant and high value industrial oilseed crop. It can be a good fit in the declining water situation of the Southern High Plains. Developing a crop model for safflower will be most useful to assess its water use footprints under different agro-ecological regions. The objective of this study was to simulate water balance, evapotranspiration and water use efficiency of spring safflower using the CROPGRO model. The model adapted previously for safflower was further calibrated based on observed soil water extraction data from an experiment conducted during 2013 and 2014 at Clovis, NM. The values of lower limit, drained upper limit, and root growth factor were adjusted to match the simulated water use results with the observed results. The observed average water content values during the growing season were 0.20, 0.24, 0.23, 0.22, 0.21, 0.21, and 0.23 cm³/cm³ for soil layers 0.1-0.3, 0.3-0.5, 0.5-0.7, 0.7-0.9, 0.9-1.1, 1.1-1.3, and 1.3-1.5 m, respectively. The corresponding simulated average water content values were 0.20, 0.20, 0.24, 0.23, 0.23, 0.23, and 0.23 cm³/cm³ with root mean square errors (RMSE) of 0.04, 0.05, 0.05, 0.04, 0.04, 0.03, and 0.03, respectively. The observed evapotranspiration (ET) and water use efficiency values, averaged across treatments, were 383 mm and 5.3 kg/ha/mm compared to simulated values of 370 mm and 5.3 kg/ha/mm, respectively. The average predicted seed yield was 1974 kg/ha which was similar to the observed seed yield of 1975 kg/ha with RMSE of 360 kg/ha. With the current water response calibration, the CROPGRO model is capable of predicting safflower water use and ET. This capability can be refined with further testing of the model under different climatic conditions.