MODELING OF FULL AND LIMITED IRRIGATION SCENARIOS FOR CORN IN A SEMIARID ENVIRONMENT

Population growth in urbanizing areas such as the Front Range of Colorado has led to increased pressure to transfer water from agriculture to municipalities. In some cases, farmers may remain agriculturally productive while practicing limited or deficit irrigation, where substantial yields may be obtained with reduced water applications during non-water-sensitive growth stages, and crop evapotranspiration (ET) savings could then be leased by municipalities or other entities as desired. Site-specific crop simulation models have the potential to accurately predict yield and ET trends resulting from differences in irrigation management. The objective of this study was to statistically determine the ability of the CERES-Maize model to accurately differentiate between full and limited irrigation treatments in northeastern Colorado in terms of evapotranspiration (ET), crop growth, yield, water use efficiency (WUE), and irrigation use efficiency (IUE). Field experiments with corn were performed near Fort Collins, Colorado, from 2006 to 2008, where four replicates each of full (100% of ET requirement for an entire season) and limited (100% of ET during reproductive stage only) irrigation treatments were evaluated. Observations of soil profile water content, leaf area index, leaf number, and grain yield were used to calibrate (2007) and evaluate (2006 and 2008) the model. Additionally, ET and water use efficiency (WUE) were calculated from a field water balance and compared to model estimates. Over the three years evaluated, CERES-Maize agreed with observed trends in anthesis date, seasonal cumulative ET (Nash-Sutcliffe efficiency E-NS = 0.966 for full irrigation and 0.835 for limited irrigation), leaf number in 2007 (E-NS = 0.949 for full irrigation and 0.900 for limited irrigation), leaf area index in 2008 (E-NS = 0.896 for full irrigation and 0.666 for limited irrigation), and yield (relative error RE = 4.1% for full irrigation and -3.4% for limited irrigation). Simulation of late-season leaf area index in limited irrigation was underestimated, indicating model overestimation of water stress. Simulated cumulative ET trends were similar to observed values, although CERES-Maize showed some tendency to underpredict for full irrigation (RE = -7.2% over all years) and overpredict for limited irrigation (RE = 12.7% over all years). Limited irrigation observations showed a significant increase in WUE over full irrigation in two of the three years; however, the model was unable to replicate these results due to underestimation of ET differences between treatments. While CERES-Maize generally agreed with observed trends for full and limited irrigation scenarios, simulation results show that the model could benefit from a more robust water stress algorithm that can accurately reproduce plant responses such as those observed in this study.