Effects of dicyandiamide, phosphogypsum and superphosphate on greenhouse gas emissions during pig manure composting

This study investigated the effects of dicyandiamide, phosphogypsum and superphosphate on greenhouse gas emissions and compost maturity during pig manure composting. The results indicated that the addition of dicyandiamide and phosphorus additives had no negative effect on organic matter degradation, and could improve the compost maturity. Adding dicyandiamide alone reduced the emissions of ammonia (NH3), methane (CH4) and nitrous oxide (N2O) by 9.37 %, 9.60 % and 31.79 %, respectively, which was attributed that dicyandiamide effectively inhibited nitrification to reduce the formation of N2O. Dicyandiamide combined with phosphogypsum or superphosphate could enhance mitigation of the total greenhouse gas (29.55 %-37.46 %) and NH3 emission (18.28 %-21.48 %), which was mainly due to lower pH value and phosphoric acid composition. The combination of dicyandiamide and phosphogypsum exhibited the most pronounced emission reduction effect, simultaneously decreasing the NH3, CH4 and N2O emissions by 18.28 %, 38.58 % and 36.14 %, respectively. The temperature and C/N content of the compost were significantly positively correlated with greenhouse gas emissions.