Use of APSIM to model nitrogen use efficiency of rain-fed wheat

Nitrogen uptake and supply directly depends upon timing and method of application, soil physical conditions, climate and plant genetic features. Therefore, it varies with location and environment. Crop simulation models can be complementary decision support tools in field experiments to develop innovative crop management systems. APSIM (Agricultural Production Systems Simulator) is software which allows dynamic simulation of crop production, residue management, soil water and nutrient flow under different timing and methods of fertilizer application. In present studies, APSIM was calibrated and validated to predict nitrogen use efficiency of wheat under rain-fed conditions for Pothwar region of Pakistan. Field experiments were laid out using RCBD four factor factorial design replicated four times at PMAS-Arid Agriculture University, Rawalpindi Research area. Two wheat genotypes were planted during years (2010-11 and 2011-12) using different nitrogen rates [N0 (No fertilizer), N50 (50kg per ha), N100 (100 kg per ha) and N150 (150 kg per ha)] and application methods by keeping individual plot size of 4m x 6m and row spacing of 25cm. Maximum nitrogen use efficiency (108.49 kg per kg) was calculated for N0 while minimum NUE (25.47 kg per kg) calculated for N150. Split dose application method gave more NUE (58.95 kg per kg) than full dose nitrogen application method (53.77 kg per kg). Genotype NARC-2009 performed better and gave maximum NUE (60.55 kg per kg), while minimum NUE (52.17 kg per kg) was calculated for Chakwal-50. Similarly, during 2010-11, more NUE (60.19 kg per kg) was calculated than 2011-12 (50.52 kg per kg). Days to maturity, biomass nitrogen, grain yield and grain nitrogen were recorded from the field experiment as well as simulated by APSIM model. The simulated outcomes for all these parameters were strongly correlated. The simulation depicted a strong dependency of the mineral nitrogen concentration upon plant nitrogen uptake and growth. The validation skill scores like R2 and RMSE confirmed the ability of APSIM to model nitrogen use efficiency in wheat under rain-fed conditions. Therefore, simulation modeling approaches should be adopted to recommend optimum fertilizer dose and timing to get maximum crop yield and eliminate nitrogen losses in the context of extreme climate variability.