ABSTRACT
Emissions of four major greenhouse gases (GHGs), that is, carbon dioxide (CO2), methane (CH4), oxides of nitrogen (nitrous oxide, N2O, and nitric oxide, NO), and the halocarbons, are bringing about major changes to the global environment. Since the 1950s, the concentrations of these gases have increased signicantly over time. The increased concentration of GHGs causes global warming, depletes the concentration of ozone in the stratosphere, and also contributes to acid deposition. Although most of the anthropogenic emissions come from the combustion of fossil fuels and from industrial processes, there is also a sizeable contribution from agriculture and land-use changes (LUCs). Agriculture accounts for an estimated emission of 5.1-6.1 Gt CO2-eq/year, including 3.3 Gt CO2-eq/year as CH4 and 2.8 Gt CO2-eq as N2O. These emissions from agriculture represent 10%–12% of the total anthropogenic emission of GHGs (Smith et al., 2007). Of the total non-CO2 emissions from agriculture, N2O emission from soils and CH4 emission from enteric fermentation comprise 38% and 32%, respectively (Figure 5.1). Biomass burning, rice agriculture, and manure management account for 12%, 11%, and 7% of the emissions, respectively (EPA, 2006). Compared to 1990, agricultural emissions of CH4 and N2O have increased by nearly 17%, representing a mean emission increase of about 60 Mt CO2-eq/year. Normally, CO2 emissions from agricultural soils are
CONTENTS
Introduction ...................................................................................................................................... 73 Carbon Dioxide Emission ................................................................................................................ 74 Methane Emission ............................................................................................................................77 Nitrous Oxide Emission ...................................................................................................................77 Mitigation Options ........................................................................................................................... 79
Carbon Dioxide ........................................................................................................................... 79 Methane ....................................................................................................................................... 82 Nitrous Oxide ..............................................................................................................................84
