Simulating maize response to nitrogen fertilizer using the critical nitrogen concentration curve

The application of crop models for simulating crop response to nitrogen (N) plays an essential role in improving agricultural management. The majority of these models involve complex equations and require several input parameters for calibration. AquaCrop simulates the crop response to different amounts of N using a semi-quantitative approach which simulates the effect of N stress on transpiration and biomass production during the growing season. This model cannot determine the proper time and amount of N fertilizer for efficient farm management. In the present study, a direct simulation approach based on the concept of a critical nitrogen curve was applied to simulate the effect of N deficiency on transpiration and biomass production. The main objective of this study was to evaluate a direct simulation approach and compare its results with the semi-quantitative approach. For this purpose, the experimental data was obtained from two years of maize cultivation. Biomass and plant nitrogen concentrations were measured during the growing season. The results showed that the RRMSE index (relative root mean square error) in biomass simulation was 4% lower on average for each treatment compared to the semi-quantitative approach. In addition, increasing N stress caused more errors in simulating B. Thus, RRMSE was 26.48 % and 30.96% for simulating B by direct approach in stressed treatments and 9.57% and 15.75 % in the non-stressed treatments. In general, these results show that the application of the concept of critical nitrogen curve in crop models provides a more accurate estimate for crops under nitrogen stress.