Mitigating Greenhouse Gas and Ammonia Emissions from Stored Slurry through the Addition of Brewing Sugar and a Biological Additive

Abstract

Livestock slurry stores are a key source of ammonia (NH3) and greenhouse gas (GHG) emissions. This study evaluated the potential to reduce NH3, CO2, CH4 and N2O emissions by adding effective microorganisms (EM) and brewing sugar to beef cattle slurry in a replicated small-scale (1 litre slurry volume) experiment. The effect of EM and brewing sugar was explored at two concentrations (5 v/w and 10% w/w respectively) and in two environments (cold and warm) over a period of 30 days slurry storage. Greenhouse gas emissions were measured by taking headspace samples from the closed vessels over a 1 hour period, whilst relative NH3 loss was quantified at the same time by placing an acid trap within the closed headspace. Brewing sugar addition induced ‘self-acidification’ of the slurry, via lactic acid production and accumulation, resulting in a decrease in slurry pH from pH 7.8 to <4.5. This was effective in lowering average NH3 loss in the cold and warm environments by 40% and 70%, respectively. Methane emissions were also reduced following the addition of brewing sugar, by up to 75%, resulting in a reduction in the cumulative total GHG (N2O + CH4 + CO2) emission (expressed as CO2 equivalent; CO2e) of 34% and 85%, respectively. The total greenhouse gas emission (CO2e) during slurry storage was dominated by CH4, representing at least 59% of total CO2e emitted. Effective microorganisms had little impact on NH3 and GHG emission, and are not deemed a useful mitigation strategy for these gases.