Greenhouse gas emissions during composting of dairy manure: Influence of the timing of pile mixing on total emissions

• We test the effect of delaying compost pile mixing on greenhouse gas(GHG) emissions.
• Delaying mixing from two to five weeks did not decrease overall GHG emissions.
• Approximately 60% of total GHG emissions occur within the first two weeks.

The effect of the timing of pile mixing on greenhouse gas (GHG) emissions during dairy manure composting was determined using large flux chambers designed to completely cover replicate pilot-scale compost piles. Approximately 50–70% of total CO2 and 75–80% of CH4 emissions occurred within the first two weeks of composting. Total GHG emissions from compost piles that were mixed at 2, 3, 4, or 5 weeks after initial construction were not significantly different from the emissions from unmixed (static) piles during a six week trial period. Although delaying initial pile mixing (2, 3, 4, or 5 weeks) generally lead to decreases in CO2 emissions, delaying mixing did not significantly affect CH4 or total GHG emissions. When normalised for degraded volatile solids (VS), CO2, CH4, N2O, and total emissions values ranged from 600--700, 130--150, 50--100, and 800–950 g CO2-eq per kg VS degraded, respectively. Carbon dioxide, methane, and nitrous oxide accounted for 75%, 14–19%, and 6–12%, respectively, of total GHG emissions from static and mixed piles.