Carbon Dioxide Emission from Ferric Luvisols: The Role of Mineral Nitrogen Fertilizers and Soil Temperature in the Guinea Savanna Agro-ecological Zone of Ghana

Abstract

Soils in the Guinea Savanna Agro-ecological zone of Ghana are inherently low in fertility, especially nitrogen. Furthermore, organic matter is very low as a result of total removal of crop residue followed by animal grazing and annual phenomenal bush burning. This has led to a reduction in soil carbon content and poor soil C:N ratio. With increase crop production, soils are amended with mineral fertilizer in most cases. In order to improve the soil carbon stocks and determine its losses in the soil, many studies have been conducted on the use of both inorganic and organic fertilizers as soil amendments and their impact on soil carbon partitioning. However, in the Guinea Savanna Agro-ecological zone of Ghana, there is paucity of information on the effects of mineral fertilizers on soil carbon emissions. Also, there are few reports of CO2 flux from soils in the Guinea Savanna agro-ecological zone of Ghana. Furthermore, there is lack of research information on the influence of hydrothermal conditions on carbon stocks in the study area. This study, sought to investigate the influence of soil-water-temperature and application of mineral N fertilizers on CO2 emissions in the Guinea Savanna agro-ecological zone of Ghana. It further determined soil CO2 emissions released per maize grain produced. It was conducted on Ferric Luvisols in the Tolon District of the Northern region of Ghana to determine the influence of mineral nitrogen (N) fertilizers and soil-temperature-water and chemical characteristics of the soil on CO2 emissions. The treatments consisted of three sources of N fertilizers: urea(U), sulphate of ammonia(SA) at 60 and 120 kg ha-1 yr-1 each and 60 kg N ha -1 yr-1 and a control(N0) arranged in a randomized completely block design replicated thrice. Omankwa, a maize cultivar, was the test crop. A plot was left without mineral N application and was used as the control. The results of the study showed that, plots of NPK 60-40-40, U 120, SA 60 and U 60 kg N ha-1 yr-1 emitted 2 to 5 times less CO2 flux compared to plots of SA 120. Additionally, application of NPK 60-40-40 kg ha-1 yr-1, SA 60 and U120 kg N ha-1 yr-1 resulted in the release of 0.9 kg CO2-C kg-1 grain emitted which was significantly higher than plots that received no mineral fertilizer. This study, therefore, concludes that although N fertilizer type and quantities applied affected CO2 emissions significantly, it was not enough to cause global warming.