Techniques for measuring gas emissions from a composting stockpile of cattle manure

Feedlot manure is a source of atmospheric ammonia (NH3), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), gases that are considered a risk to the environment. However, accurate estimates of emission of these gases from stockpiled manure are sparse due the lack of suitable measuring techniques. In our study, the integrated horizontal flux (IHF) and the backwards Lagrangian stochastical (bLS) dispersion micrometeorological techniques were adapted to measure gas emissions (NH3, CH4, N2O and CO2) from a manure pile. The results were compared with measurements using the static chamber technique. Net horizontal gas fluxes were determined by mounting passive NH3 samplers, gas intakes for CO2 and CH4, and anemometers on poles that were always located up- and downwind of the pile as controlled by a wind vane. Further, NH3 emission was estimated with the bLS technique using NH3 concentration measured with a laser downwind of the pile. NH3 emission measured with the IHF and bLS techniques were similar. Periodic measurements of emissions of CO2 with the IHF technique by taking air samples with syringes and measuring CO2 and CH4 concentrations on a gas chromatograph, were similar to continuous measurements with the IHF technique measuring gas concentrations with an infrared gas monitor. Emissions of CO2, CH4 and N2O measured with the static vented chamber technique were 12–22% of that measured with the IHF technique. Our results show that measurements of gas emission from stockpiled manure depend on the measuring technique and emphasizes the need for further validation of these techniques.