Liquid manure (slurry) storages are sources of gases such as ammonia (NH3) and methane (CH4). Danish slurry storages
are required to be covered to reduce NH3 emissions and often a floating crust of straw is applied. This study investigated whether physical properties of the crust or crust microbiology had an effect on the emission of the potent greenhouse gases CH4 and nitrous oxide (N2O) when crust moisture was manipulated (“dry”, “moderate”, and “wet”). The dry crust had the deepest oxygen penetration (45 mm as compared to 20 mm in the wet treatment) as measured with  microsensors, the highest amounts of nitrogen oxides (NO2 – and NO3–) (up to 36 μmol g–1 wet weight) and the highest emissions of N2O and CH4. Fluorescent in situ hybridization and gene-specific polymerase chain reaction (PCR) were used to detect occurrence of bacterial groups. Ammonia-oxidizing bacteria (AOB) were abundant in all three crust types, whereas nitrite-oxidizing bacteria (NOB) were undetectable and methane-oxidizing bacteria (MOB) were only sparsely present in the wet treatment. A change to anoxia did not affect the CH4 emission indicating the virtual absence of aerobic methane oxidation in the investigated 2-mo old crusts. However, an increase in N2O emission was observed in all crusted treatments exposed to anoxia, and this was probably a result of denitrification based on NOx – that had accumulated in the crust during oxic conditions. To reduce overall greenhouse gas emissions, floating crust should be managed to optimize conditions for methanotrophs.

For more information the full article can be found at https://www.agronomy.org/publications/jeq