Effects of Two Manure Additives on Methane Emissions from Dairy Manure

SIMPLE SUMMARY: Livestock farms often store liquid manure until it can be used to fertilize crops. During anaerobic storage, the manure produces methane, which is a greenhouse gas. Many livestock farms add special chemical products to the manure that are said to control odours or increase fertilizer value. We wanted to know if these additives change the amount of methane produced. Two additives that are commonly used by farmers in many countries were tested in the laboratory. We mixed liquid dairy manure with different amounts of these products and measured the amount of methane produced over 30 to 90 days. Results were then compared to the same manure without any product. These tests were done at two temperatures, around 37 °C (a typical biodigester temperature), and 20 °C (a typical manure storage temperature). We also compared the chemical and physical properties of manure. We found that adding these products did not change the amount of methane produced, and it did not change the chemical and physical properties of the manure related to methane production. These findings suggest that farms using these products can be expected to have normal methane emissions from stored manure. ABSTRACT: Liquid manure is a significant source of methane (CH(4)), a greenhouse gas. Many livestock farms use manure additives for practical and agronomic purposes, but the effect on CH(4) emissions is unknown. To address this gap, two lab studies were conducted, evaluating the CH(4) produced from liquid dairy manure with Penergetic-g(®) (12 mg/L, 42 mg/L, and 420 mg/L) or AgrimestMix(®) (30.3 mL/L). In the first study, cellulose produced 378 mL CH(4)/g volatile solids (VS) at 38 °C and there was no significant difference with Penergetic-g(®) at 12 mg/L or 42 mg/L. At the same temperature, dairy manure produced 254 mL CH(4)/g VS and was not significantly different from 42 mg/L Penergetic-g(®). In the second lab study, the dairy manure control produced 187 mL CH(4)/g VS at 37 °C and 164 mL CH(4)/g VS at 20 °C, and there was no significant difference with AgrimestMix (30.3 mL/L) or Penergetic-g(®) (420 mg/L) at either temperature. Comparisons of manure composition before and after incubation indicated that the additives had no effect on pH or VS, and small and inconsistent effects on other constituents. Overall, neither additive affected CH(4) production in the lab. The results suggest that farms using these additives are likely to have normal CH(4) emissions from stored manure.