Ammonia, nitrous oxide and methane emissions from differently stored dairy manure derived from grass- and hay-based rations

The effects on nitrogen losses and volatilisation of ammonia, methane and nitrous oxide from manure storage were investigated using excreta of dairy cows fed two forage-based rations, (i) young grass (ad libitum) and hay (2 kg d(-1)) or (ii) hay (ad libitum) and concentrate (3 kg d(-1)). In two series either grass of low crude protein content (112 g kg(-1) dry matter, similar to the hay) or of high crude protein content (229 g kg(-1)) was used. Emissions from the resulting manures were investigated in two common storage systems, the liquid manure system and the slurry/farmyard manure system. Storage was performed under controlled conditions using the chamber technique to quantify trace gas emissions and the mass balance method to measure total nitrogen loss. The ration characterised by the low-protein grass resulted in higher urinary nitrogen and lower faecal nitrogen excretion than the hay ration, thus significantly enhancing total nitrogen and ammonia emissions from all types of manure. Differences to the hay ration were, however, far more pronounced feeding the high-protein grass, with the emissions of nitrogen and ammonia accounting for the 3- to 4-fold level of that of the hay ration. Initial differences of the manures in nitrogen content had partly disappeared after storage yielding manures which differed less in nitrogen fertiliser value than the fresh manures. In some but not all manure types there was a certain decrease in nitrous oxide emission feeding grass instead of hay. Methane release was low with the high-protein grass of series 2. Total nitrogen losses during 5 to 7 weeks of storage were lowest with farmyard manure (11% of initial nitrogen), followed by liquid manure (19%) and slurry (30%). Calculated for the daily manure amount per cow, greenhouse gas emissions from 5 to 7 weeks stored manure were higher in the slurry/farmyard manure system than in the liquid manure system (2.4 vs 1.5 kg CO(2) equivalents).