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

Abstract

Theeffects on nitrogen losses and volatilisation of ammonia, methane and nitrousoxide from manure storage were investigated using excreta of dairy cows fed twoforage-based rations, (i) young grass (ad libitum) and hay (2 kgd−1) or (ii) hay (ad libitum) and concentrate (3kg d−1). In two series either grass of low crudeprotein content (112 g kg−1 dry matter, similar tothe hay) or of high crude protein content (229 gkg−1) was used. Emissions from the resulting manureswere investigated in two common storage systems, the liquid manure system andthe slurry/farmyard manure system. Storage was performed under controlledconditions using the chamber technique to quantify trace gas emissions and themass balance method to measure total nitrogen loss. The ration characterised bythe low-protein grass resulted in higher urinary nitrogen and lower faecalnitrogen excretion than the hay ration, thus significantly enhancing totalnitrogen and ammonia emissions from all types of manure. Differences to the hayration were, however, far more pronounced feeding the high-protein grass, withthe emissions of nitrogen and ammonia accounting for the 3- to 4-fold level ofthat of the hay ration. Initial differences of the manures in nitrogen contenthad partly disappeared after storage yielding manures which differed less innitrogen fertiliser value than the fresh manures. In some but not all manuretypes there was a certain decrease in nitrous oxide emission feeding grassinstead of hay. Methane release was low with the high-protein grass of series2.Total nitrogen losses during 5 to 7 weeks of storage were lowest with farmyardmanure (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 theslurry/farmyard manure system than in the liquid manure system (2.4 vs 1.5kg CO2 equivalents).