Determining optimum plant density and nitrogen rate using field experiment and model simulation.

Poor crop management practices are key factors leading to a significant reduction in durum wheat yield in the central highlands of Ethiopia. The aim of this study was to determine optimum plant density and nitrogen rate that increase durum wheat productivity while reducing environmental impacts. A combination of data from field experiments conducted from 2017 to 2020 under rainfed conditions and simulation data of CERES-Wheat model were used for this study. The CERES-Wheat model was calibrated for Utuba cultivar from 3-years (2017-2019) field experiment data. The model was further evaluated with the experimental data conducted during the 2020 cropping season under four plant densities and four nitrogen fertilizer rates. Because of differences in temperature and rainfall patterns during the potential growing season, seasonal analysis was used to determine the optimum plant density and N rate using 37 years (1985-2022) of historical weather data. The simulation results suggested that 275 plants m^-2 with an application of 200 kg ha^-1 N increased grain yield, improved nitrogen use, and produced the highest economic return while minimizing environmental risk under rainfed conditions. Compared with the current plant density (175 plants m^-2) and N fertilizer (100 kg ha^-1) an increase in plant density to 275 plants m⁻² with 200 kg ha⁻¹ N resulted in a 49% increase in grain yield by about 49%, N use efficiency by 23% with the highest net return (2114 US$ ha^-1). In general, this study showed that the CERES-Wheat model can be a promising tool for providing crop management recommendations under rainfed durum wheat farming.