Linking manure composition to manured soil emissions of ammonia and greenhouse gases

Estimating carbon (C) and nitrogen (N) losses from agricultural soils is crucial to maintain sustainable soil management. Many models that calculate atmospheric fluxes from manured soils depend on emission factors that do not consider differences between manure from different animals, let alone manure composition information within manure type. In a series of mesocosm incubation experiments, we quantified gaseous C and N emissions from 50 different dairy manures with the aim to link emission magnitude to manure composition. In short lab trials, the emission potential of ammonia (NH3) and methane (CH4) from manures was determined, after which NH3, nitrous oxide (N2O), and carbon dioxide (CO2) emissions after manure application at 100 kg N/ha to soil were measured during a 21-day incubation experiment. In both cases gas concentrations were measured using an INNOVA 1512 photoacoustic gas analyser. A combination of principle component analysis and multiple regression with mixed linear models was applied to investigate the relationship between manure composition and gaseous emissions. Results showed that not total or ammoniacal N, but rather manure pH was the main factor explaining NH3 emissions. The N2O emissions, and to a lesser extent the CO2 emissions, were conditioned by the amount of moisture added with the manure. Other significant factors in the best models were organic C and N, and C/N ratio. This study shows that the variability of emission potential is high within one manure type. Including easily obtainable information on manure composition, such as pH and nutritional content, could provide a way to improve manured soils emission calculations.