Although greenhouse gases (GHGs) like carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) occur naturally in the atmosphere, human activities have changed their atmospheric concentrations (IPCC, 2006). Agricultural sources are the largest global source of non-CO2 emissions. Nitrous oxide emissions from agricultural soils and methane from enteric fermentation in livestock account for nearly 70% of the emissions from this category (IPCC, 2006 and EPA, 2006).