Nitrous oxide () and methane () are the two major greenhouse gasses (GHG) emitted by agricultural activities. accounts for around 8% of the warming impact of current human GHG emissions. Agricultural activities that directly increase emissions are: fertilization, application of manure or other organic materials, retention of crop residues, production of nitrogen-fixing crops and forages, and cultivation of soils with high organic matter content. Irrigation, drainage, tillage practices and fallowing of land also increase emission.