Effects of Cattle Slurry Acidification on Ammonia and Methane Evolution during Storage

Abstract

Slurry acidification before storage is known to reduce NH₃ emissions, but recent observations have indicated that CH₄ emissions are also reduced. We investigated the evolution of CH₄ from fresh and aged cattle slurry during 3 mo of storage as influenced by pH adjustment to 5.5 with sulfuric acid. In a third storage experiment, cattle slurry acidified with commercial equipment on two farms was incubated. In the manipulation experiments, effects of acid and sulfate were distinguished by adding hydrochloric acid and potassium sulfate separately or in combination, rather than sulfuric acid. In one experiment sulfur was also added to slurry as the amino acid methionine in separate treatments. In each treatment 20-kg portions of slurry (n = 4) were stored for 95 d. All samples were subsampled nine to 10 times for determination of NH₃ and CH₄ evolution rates using a 2-L flow-through system. In all experiments, the pH of acidified cattle slurry increased gradually to between 6.5 and 7. Acidification of slurry reduced the evolution of CH₄ by 67 to 87%. The greatest reduction was observed with aged cattle slurry, which had a much higher potential for CH₄ production than fresh slurry. Sulfate and methionine amendment to cattle slurry without pH adjustment also significantly inhibited methanogenesis, probably as a result of sulfide production. The study suggests that complex microbial interactions involving sulfur transformations and pH determine the potential for CH₄ emission during storage of cattle slurry, and that slurry acidification may be a cost-effective greenhouse gas mitigation option. Copyright © 2012. . Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.