Methane and carbon dioxide emissions from manure storage facilities at two free-stall dairies

• Significant carbon dioxide emissions occur from dairy waste.
• The global greenhouse warming potential of dairy manure storage emissions of CH4 was 8–10 times that of CO2.
• Manure solids separation prior to storage greatly reduces the storage CH4 and CO2 emissions.
• Warmer weather increases the mass ratio of CH4–CO2 emissions of dairy manure.

Manure management by dairies is estimated to account for 6% of the greenhouse gas warming potential of all agricultural emissions in the USA. Emissions methane (CH4) and carbon dioxide (CO2) were measured from manure storage facilities at two Midwestern dairies (an Indiana lagoon and two Wisconsin basins). The CH4 concentrations were measured using photoacoustic infrared absorption spectroscopy and flame ionization gas chromatography. The CO2 concentrations were measured using photoacoustic infrared absorption spectroscopy and non-dispersive infrared spectroscopy. Emissions were estimated using a backward Lagrangian Stochastic model with on-site turbulence measurements.The WI basins emitted more CH4 and CO2 than the waste lagoon in IN on an animal basis. Peak emissions were episodic. Mean daily CH4 emissions during the fall (October) from the WI basins and IN lagoon were 295 g hd−1 d−1 (374 g AU−1 d−1) and 47 g hd−1 d−1 (59 g AU−1 d−1), respectively. Mean CO2 emissions during the fall were 575 g hd−1 d−1 (374 g AU−1 d−1) from the WI basins (October) and 107 g hd−1 d−1 (135 g AU−1 d−1) from the IN lagoon (September). Emissions were not resolvable (approximately emissions MDL) when the storage area surface was frozen. Methane emissions contributed eight–ten times the radiative warming potential of CO2 (animal basis) at both dairies. Mean daily CO2-equivalent emissions from the WI basins (IN lagoon) ranged from highs of 7.9 kg CO2-e hd−1 d−1 in October (2.6 kg CO2-e hd−1 d−1 in September) to lows of 1.6 kg CO2-e hd−1 d−1 (0.4 kg CO2-e hd−1 d−1) in December through January. Air temperature was correlated with CH4 and CO2 emissions at the WI basin but not the IN lagoon. Wind speed was weakly correlated with CH4 emissions (but not CO2 emissions) at both dairies. While weather conditions were similar, the separation of solids prior to storage contributed to lower CH4 and CO2 emissions and lower greenhouse warming potential per animal. Cooler climatic conditions decreased CH4 and CO2 emissions as well as decreasing the mass ratio of CH4–CO2 emissions.