Field Validation of the DNDC-Rice Model for Crop Yield, Nitrous Oxide Emissions and Carbon Sequestration in a Soybean System with Rye Cover Crop Management

The DNDC-Rice model effectively simulates the yield and greenhouse gas emissions within paddy system, while its performance under upland conditions remains unclear. This study validated the model using data from a long-term cover crop experiment (fallow [FA] and rye [RY]) in a soybean field, evaluating its limitations in upland systems simulation. The model underestimated water-filled pore space (WFPS) and nitrous oxide (N2O) flux while overestimating soybean biomass, yield, and carbon dioxide (CO2) flux. The underestimation of cumulative N2O flux (25.6% in FA and 5.1% in RY) was attributed to both underestimated WFPS and algorithm’s limitations in simulating N2O emission pulses. Overestimated soybean growth increased respiration, leading to the overestimation of CO2 flux. Although the model captured trends in soil organic carbon (SOC) stock, the simulated annual values differed from observations (-9.9% to +10.1%), potentially due to sampling errors. Both observed and simulated results showed that RY increased N2O emissions and SOC stock compared to FA. However, enhanced SOC sequestration under RY offset the increased N2O emissions, resulting in a lower net global warming potential than FA. These findings indicate that the DNDC-Rice model requires improvements in its nitrogen cycling algorithm and crop growth sub-models to improve predictions for upland systems.