Emissions of ammonia, nitrous oxide and methane from different types of dairy manure during storage as affected by dietary protein content

In a storage experiment with dairy cow manure, the effects of dietary prote in content and manure type on ammonia, nitrous oxide and methane volatiliza tion as well as overall nitrogen (N) loss from manure were investigated. Ea rly-lactating cows received rations with 175, 150 and 125 g crude protein/k g dry matter. Each ration was tested in four manure storage systems reflect ing typical farm conditions. These either contained total excreta with high amounts of straw (deep litter manure) or no straw (slurry) or, proportiona tely, 0.9 of urine and 0.1 of faeces (urine-rich slurry) complemented by th e residuals with a low amount of straw (farmyard manure). Manure samples we re stored for 7 weeks under controlled conditions and trace gas emission wa s repeatedly measured. Reduction of N intake decreased daily N excretion an d urine N proportion and, on average, led to 0.7-fold lower storage ammonia emission rates on average. Total storage N loss was simultaneously reduced with the extent depending on urine N proportion of the respective manures. A lower dietary protein content furthermore reduced nitrous oxide emission rates in most manure types but increased methane emission from urine-rich slurry; however, global warming potential (based on trace gas output) of al l manures was similar with low and high dietary protein content. In deep li tter manure, characterized by the highest C: N ratio, emission rates of tot al N, ammonia and methane were lowest, whereas nitrous oxide values were in termediate. Substantial emission of nitrous oxide occurred with farmyard ma nure which also had the highest methane values and, consequently, by far th e highest global warming potential. C: N ratio of manure was shown to be su itable to predict total N loss from manure during storage in all manure typ es whereas urine N proportion and manure pH were only of use with liquid ma nures.