Measurement and Modeling Nitrous Oxide Emissions from Ferric Luvisols in the Guinea Savanna Agro-ecological Zone of Ghana

Abstract

Agricultural sector in Ghana contributes to about 60% of Gross Domestic Product (GDP) and is mainly characterized by fertilizer application to improve depleting soil fertility. With the increase in population and demand for increased productivity, application of inorganic fertilizers will result in enhanced greenhouse gas emissions. As nitrogen (N) is among the most limiting soil nutrient in the Guinea Savanna, chemical/organic fertilizers are applied in significant amounts to maintain crop productivity. Because of increased fertilizer and manure application to replenish dwindling soil fertility, the region is likely to become a significant source of nitrous oxide (N2O) emissions. To study the effect of fertilizer application on N2O emissions, Denitrification decomposition model (DNDC), a process-base model of carbon (C) and nitrogen (N) biogeochemistry in agricultural ecosystems was calibrated with field data obtained in 2013 and was used to predict the impact of N fertilizer source and rate of application on N2O emissions. The linear equation between measured and modeled annual fluxes from ferric luvisols showed a positive relationship between observed N2O fluxes from field experiments in the 2013 season and simulated N2O flux with with a coefficient of determination (R2) of 0.7773. For the validation period (2013) the predicted N2O emissions simulation agreed practically well with the observed data. Plots without fertilization resulted in the lowest N2O emissions in both measured and simulated data and the model was capable of simulating the highly dynamic changes in N2O emissions most of the time at different N application. However, N2O emissions on application of 120 kg N ha-1 as urea and sulphate of ammonia were underestimated by DNDC model. The results further showed that the DNDC model can be used to predict N2O gas flux from the Guinea Savanna agro-ecological conditions of Ghana. Simulated results further indicate that, application of 120 kg N ha-1 as sulphate of ammonia and urea respectively would had higher global warming potential compared to application of same N source at 60 kg N ha-1.