Predicting nitrous oxide emissions from manure properties and soil moisture: An incubation experiment

• N2O emissions from manure-amended soil at three moisture levels were quantified.
• Emission factors (0.04–2.4% of total N) varied systematically with manure type and WFPS.
• An empirical model of N2O emissions from manure could not predict emissions.
• A term linking anaerobic decomposition to relative soil gas diffusivity was introduced.
• Both 15N2O data and model results identified denitrification as the main source of N2O.

Field-applied manure is a source of essential plant nutrients, but benefits may be partly offset by high rates of nitrous oxide (N2O) emissions, as modified by manure characteristics and soil properties. In a 28-d incubation experiment we quantified short-term emissions of N2O from a sandy loam soil amended with digestate (DI), pig slurry (PS) or cattle slurry (CS), and unamended soil (Ctrl), when incubated at 60, 70 and 80% water-filled pore space (WFPS). The soil was amended with 15N-labelled nitrate to distinguish sources of N2O. Emissions of N2O were not related to N input and corresponded to between 0.04 and 2.42% of manure N, decreasing in the order CS > DI > PS > Ctrl within each WFPS level. Recovery of 15N in N2O indicated that heterotrophic denitrification constituted at least 64–77% of total emissions at 70 and 80% WFPS, while nitrification was more important for the low emissions at 60% WFPS. The results were further analyzed with a static two-compartment model of N2O emissions from manure. Experimental results showed a much stronger response to soil moisture than predicted by the model, and therefore a new term was introduced linking the balance between aerobic and anaerobic decomposition to relative soil gas diffusivity. Model parameters for sources of N2O, estimated from experimental results by multiple linear regression, indicated that denitrification was responsible for 79–98% of N2O emissions at 70 and 80% WFPS, and 45–59% at 60% WFPS.