Algorithms for calculating methane and nitrous oxide emissions from manure management

Biogenic emissions of methane (CH(4)) and nitrous oxide (N(2)O) from animal manure are stimulated by the degradation of volatile solids (VS) which serves as an energy source and a sink for atmospheric oxygen. Algorithms are presented which link carbon and nitrogen turnover in a dynamic prediction of CH(4) and N(2)O emissions during handling and use of liquid manure (slurry). A sub-model for CH(4) emissions during storage relates CH(4) emissions to VS, temperature and storage time, and estimates the reduction in VS. A second sub-model estimates N(2)O emissions from field-applied slurry as a function of VS, slurry N and soil water potential, but emissions are estimated using emission factors. The model indicated that daily flushing of slurry from cattle houses would reduce total annual CH(4)+N(2)O emissions by 35% (CO(2) eq.), and that cooling of pig slurry in-house would reduce total annual CH(4)+N(2)O emissions by 21% (CO(2) eq.). Anaerobic digestion of slurry and organic waste produces CH(4) at the expense of VS. Accordingly, the model predicted a 90% reduction of CH(4) emissions from outside stores with digested slurry, and a >50% reduction of N(2)O emissions after spring application of digested as opposed to untreated slurry. The sensitivity of the model towards storage temperature and soil water potential was examined. This study indicates that simple algorithms to account for ambient climatic conditions may significantly improve the prediction of CH(4) and N(2)O emissions from animal manure.