Present and potential impacts of waste from poultry production on the environment

Poultry production is associated with greenhouse gas (GHG) emissions but at a much lower extent than other livestock. Global production of nitrogen from poultry excreta has been estimated at about 3.29 million metric tons for meat type chickens (the average of two estimates with different assumption of 2.65 and 3.94 million metric tons) and 2.36 million metric tons for laying hens. These estimates are markedly below earlier estimates, suggesting that the issues related to loading are of a markedly smaller magnitude than previously envisioned. However, if it is assumed that 2% of the nitrogen is lost as nitrous oxide with a global warming potential (GWP) of 298 CO2 equivalents (eq.) per unit as GHG, poultry waste is contributing 33.7 million metric tons of CO2 eq./year or 0.0337 gigatons (Gt) CO2 eq./yr. This represents only 0.64% of agricultural GHG emissions. The preferred method for the disposal of poultry excreta is land application as a fertiliser with the aggregate of livestock and poultry excreta being applied to 0.3 million hectares in the USA. The environmental consequences of excreta in litter include the release of ammonia and nitrous oxide (a GHG) together with contamination of ground and surface water with nitrate, phosphate and pathogens. Alternative approaches to utilise used litter are the following: combustion, gasification, digestion and feeding to ruminants. There is scope to reduce the environmental impact of poultry production on the environment.