PSV-14 The effects of calcium cyanamide on greenhouse gases, ammonia emissions, and the microbiome of dairy cattle lagoon water

Abstract Dairy manure management is responsible for a significant amount of greenhouse gas emissions (GHG) in California. Aside from redesigning infrastructure to adopt alternative manure management systems, there are few options available to farmers to mitigate emissions without substantial financial investment. Calcium cyanamide, a new manure additive, showed significant reductions in GHG emissions when applied to fresh dairy cow slurry, but has not been tested on dairy lagoon water. The aim of the present study was to investigate the effects of calcium cyanamide on GHG and NH3 emissions and the microbiome of dairy lagoon water. Lagoon water was collected from a commercial dairy, and distributed into 12 stainless steel barrels. Three treatments (n = 4/treatment) of different doses of calcium cyanamide were tested: high (LW-HD; 1 kg/m3 lagoon water), low (LW-LD; 0.5 kg/m3 lagoon water), and control with no calcium cyanamide (LW-CONT; n = 4). Each barrel was sampled over two, 14-d periods, staggered to four barrels at a time, using OdoFlux chambers to monitor emissions for carbon dioxide (CO2,), methane (CH4), nitrous oxide (N2O), and ammonia (NH3). Treatments LW-LD and LW-HD contained significantly more total solids, total nitrogen and total carbon compared with LW-CONT. There was also a significantly greater concentration of acetic acid in LW-LD and LW-HD treatments compared with LW-CONT. CO2 emissions in LW-LD and LW-HD were 2.96% and 12.03% less than LW-CONT. CH4 emissions in LW-LD and LW-HD were 80.9% and 85.13% less compared with LW-CONT. N2O emissions in LW-LD and LW-HD were 81.1% and 82.66% less than LW-CONT. However, NH3 fluxes were greater in LW-LD and LW-HD compared with LW-CONT by 65.26% and 65.73%, respectively. The microbiome of the lagoon water was also affected, with reductions in relative abundance of the Proteobacteria phylum responsible for nitrification in LW-LD and LW-HD and increases in the Firmicutes phylum containing acetogenic bacteria. Calcium cyanamide could inhibit methanogenesis by increasing acetogenic bacteria that compete with methanogens for fermentation substrates. Further research is needed to investigate the efficacy of calcium cyanamide in a commercial lagoon setting.