Greenhouse Gas Emission From Stockpiling Cattle Feedlot Manure.

The use of dried distillers' grains with solubles (DDGS) in feedlot cattle diets is increasing as the bio-ethanol industry expands. This study investigated greenhouse gas (GHG) emission from stockpiled manure of cattle fed diets with wheat DDGS. There were four treatments, corresponding to four finishing cattle diets, (1) Control: manure from cattle on the standard western Canadian finishing diet of 82.5% barley grain, 15% silage (DM basis); (2) DG₂₅: manure from cattle fed 62.5% barley grain, 10% barley silage and 25% DDGS, (3) DG₃₀: manure from cattle fed 62.5% barley grain, 5% barley silage and 30% DDGS; and (4) DG₃₅: manure from cattle fed 62.5% barley, 0% barley silage and 35% DDGS. The mineral supplement made up the remaining 2.5% of the diets. For the stockpile experiment, manure, bedded with straw, was cleaned out of feedlot pen at the end of July, 2010 and stockpiled on a clay pad. Two replicated piles were constructed for each type of manure. Each manure pile was approximately 13-15 m in length, 4.0 m in width, 1.8 m in height and weighed about 40 to 55 tonne (wet weight). Following construction, GHG emissions were collected weekly using two vented static chambers from each manure stockpile for 314 days. Emissions peaked on day eight with most emissions occurring in the first 42 days, and decreased to near zero thereafter for CO₂ and CH₄. The rate of N₂O emission also peaked on day eight, but decreased gradually over time. The average emission rates over the first three months ranged from 2.70 to 3.92 g C m^-2d^-1 for CH₄ and from 0.049 to 0.065 g N m^-2d^-1 for N₂O, with no differences (P>0.05) among the four types of manure. On the other hand, CO₂ emissions from Control (40.2 g C m^-2d^-1) were higher (P<0.065) than from the three DDG manures (21.0, 19.8, and 27.6 g C m^-2d^-1, for DDG25, DDG30 and DDG35, respectively). However, the average rates of CH₄, CO₂ and N₂O emissions over 314 days did not differ significantly among treatments. It appears that including wheat DDG up to 35% DM in cattle diet had minimal effect on the rate of CH₄ and N₂O surface emission during cattle manure stockpiling.