Nitrous oxide production by manure samples collected from six manure-handling systems

Stored manures are often considered to be source of nitrous oxide (N 2 O). A study was done to identify manure characteristics and handling stages related to N 2 O production. In two laboratory experiments we investigated the production of N 2 O from several animal manures collected at different stages of manure handling or locations in stored-manure systems. Denitrifying enzyme activity, denitrification and CO 2 production rates and chemical and fibre characteristics of manure samples were also determined. Most samples had low rates of N 2 O production. Exceptions were open piles of fresh beef manure and the moist surface layer near the base of an open pile of poultry manure. Production of N 2 O was most highly correlated with nitrite plus nitrate (NO 2 − + NO 3 − ) content of manure regardless of whether results were expressed on a wet or a dry weight basis. Denitrification was the most probable source of N 2 O because N 2 O production with acetylene and denitrifying enzyme activities was higher than N 2 O production without acetylene. Stored manure is potentially an important source of N 2 O emissions, particularly when storage conditions are conducive to formation of (NO 2 − + NO 3 − ). Key words: Nitrous oxide production, denitrification, denitrifying enzyme activity, manure