Calcium cyanamide reduces methane and other trace gases during long-term storage of dairy cattle and fattening pig slurry

Abstract

Calcium cyanamide (CaCN2) has been used in agriculture for more than a century as a nitrogen fertilizer with nitrification inhibiting and pest-controlling characteristics. However, in this study, a completely new application area was investigated, as CaCN2 was used as a slurry additive to evaluate its effect on the emission of ammonia and greenhouse gases (GHG) consisting of methane, carbon dioxide, and nitrous oxide. Efficiently reducing these emissions is a key challenge facing the agriculture sector, as stored slurry is a major contributor to global GHG and ammonia emissions. Therefore, dairy cattle and fattening pig slurry was treated with either 300 mg kg−1 or 500 mg kg−1 cyanamide formulated in a low-nitrate CaCN2 product (Eminex®). The slurry was stripped with nitrogen gas to remove dissolved gases and then stored for 26 weeks, during which gas volume and concentration were measured. Suppression of methane production by CaCN2 began within 45 min after application and persisted until the storage end in all variants, except in the fattening pig slurry treated with 300 mg kg−1, in which the effect faded after 12 weeks, indicating that the effect is reversible. Furthermore, total GHG emissions decreased by 99% for dairy cattle treated with 300 and 500 mg kg−1 and by 81% and 99% for fattening pig, respectively. The underlying mechanism is related to CaCN2-induced inhibition of microbial degradation of volatile fatty acids (VFA) and its conversion to methane during methanogenesis. This increases the VFA concentration in the slurry, lowering its pH and thereby reducing ammonia emissions.