Estimating nitrous oxide, ammonia and methane emissions from dairy cow manure during storage and following application to pasture

Housing dairy cattle off-paddock in animal confinement facilities provides an alternative to grazing winter crops in southern New Zealand, but the associated greenhouse gas (GHG) emissions from such systems are poorly understood. Nitrous oxide (N2O), methane (CH4) and ammonia (NH3) emissions were measured from stored and land-applied dairy manures collected from winter-housed cows. Emissions increased with storage period, suggesting that losses could be minimised by reducing the storage period, provided ground conditions are suitable for manure spreading and there is minimal risk of nutrient run-off/leaching. After land application, NH3 emissions varied according to manure type, whereas N2O and CH4 emissions were negligible. The rate of manure application did not influence emission factors for any of the three GHGs. When manure emissions were converted to carbon dioxide equivalents (CO2e) per wintered cow, it was found that relative GHG emissions from manure were greatest during storage compared with land application, although these results require verification on a farm scale.