Evaluating the validity and sensitivity of the DNDC model for Shimajiri dark red soil

The validities of the DeNitrification-DeComposition (DNDC) model and the simulation parameters were examined by using the experimental data obtained at Miyako Branch of Okinawa Prefectural Agricultural Research Center. The obtained simulation results were compared with the observed values and it was concluded that the simulation with the measured parameters could produce better simulation results than the simulation with the model provided default parameters. The model seemed to be able to predict the total amounts of leached water and nitrate and N₂O emissions reasonably well, but the modifications in the model seemed to be still needed for capturing precise seasonal leaching and emission patterns. The sensitivity of the model was analyzed by either increasing or decreasing one of the crop and soil parameters by 25% while holding all other parameters and inputs constant. The changes in water filled porosity at field capacity were found to have the largest effects on the amount of leached water and N₂O emissions. The amount of leached nitrate was affected by the changes in water filled porosity at field capacity only slightly, but it was reduced significantly by an increase in soil pH.