Mitigation of greenhouse gas emission from the cattle manure composting process by use of a bulking agent

The greenhouse gas (GHG) [methane (CH4) and nitrous oxide (N2O)] mitigation effects of mixing dried grass into passively-aerated manure during the composting process (which accounts for 68.7% of Japanese dairy manure management) were assessed. Gaseous emissions [CH4, N2O, carbon dioxide (CO2) and ammonia (NH3)] from about 4t of fresh dairy manure with or without 400kg of dried grass mixed in were measured by the dynamic chamber method. The addition of dried grass contributed to a decrease in GHG emissions from 20.8 +/- 1.3gkg1 volatile solids (VS) to 5.4 +/- 1.4gkg1 VS (74.3% mitigation) for CH4 and from 7.4 +/- 2.6g N2O-N kg1 Ninitial to 2.7 +/- 0.4g N2O-N kg1 Ninitial (62.8% mitigation) for N2O. By applying this strategy, the expected reduction of GHG emission would be 70,466t CH4 yr1 and 1379t N2O-N yr1 (1907Gg CO2 eq. yr1 in total) in the Japanese dairy sector. On the other hand, it was showed that CO2 and NH3 emissions increase [from 424.4 +/- 214.9g CO2 kg1 VS to 603.8 +/- 99.6g CO2 kg1 VS for CO2 and from 16.9 +/- 7.1g ammonium-nitrogen (NH3-N) kg1 Ninitial to 38.3 +/- 3.5g NH3-N kg1 Ninitial for NH3] by this method. Moreover, the mechanism of this significant N2O mitigation effect cannot be explained, and a better understanding of this effect could further improve the GHG mitigation strategy.