Methane emissions from dairy lagoons in western U.S.

Methane (CH4) generation from dairy liquid storage systems is a major source of agricultural greenhouse gas emissions. However, there has been little on-farm research conducted to estimate these emissions and determine the factors that may affect these emissions. Six lagoons in south-central Idaho were monitored for one year, with CH4 emissions estimated by inverse dispersion modelling. Lagoon characteristics thought to contribute to CH4 emissions were also monitored over this time period. Average emissions from the lagoons ranged from 30 to 126 kg/ha/d or 22 to 517 kg/d. While there was a general trend for greater emissions during the summer, when temperatures were greater, events such as pumping, rainfall, freeze/thaw of lagoon surfaces, and wind events significantly increased CH4 emissions irrespective of temperature. Lagoon physicochemical characteristics such as total solids, chemical oxygen demand, and volatile solids were highly correlated with emission. Methane prediction models were developed using volatile solids, wind speed, air temperature and pH as independent variables. The USEPA methodology for estimating CH4 emissions from manure storage was used for comparison of on-farm CH4 emissions from one of the lagoon systems. The USEPA method underestimated CH4 emissions by 48%. An alternative methodology, using volatile solids degradation factor, provided a more accurate estimate of annual emissions from the lagoon system and may hold promise for applicability across a range of dairy lagoon systems in the U.S