Sulfate Additives Cut Methane Emissions More Effectively at Lower Liquid Manure Storage Temperatures

Abstract

Reducing methane (CH₄) emissions from dairy farms is a key objective in limiting total greenhouse gas emissions from the livestock industry. Reducing CH₄ emissions from manure storage using additives may provide an achievable near-term contribution to this long-term goal in alignment with the International Dairy Federation’s initiative on pathways to net zero. Sulfate-based H₂SO₄ and the sulfate-containing nonacid CaSO₄ have effectively suppressed methane emissions in lab studies at a single temperature. The present study analyzes the effect of temperature on the efficacy of these two additives, bridging the gap between common laboratory conditions and average on-farm temperature. We found superior cumulative suppression, higher peak suppression, and longer duration of high-end suppression at lower temperatures when comparing controls to additive experiments at 24, 21, and 18 °C over 120 days. Peak mitigation increased as temperature decreased, culminating at 82.9% and 57.6% for H₂SO₄ and CaSO₄, respectively, at 18 °C. Additives remained effective for longer at lower temperatures, with H₂SO₄ maintaining ≥70% peak mitigation (PM) for 102 days at 18 °C, but only 48 days at 24 °C; CaSO₄ retained ≥70% PM for 87 days at 18 °C, but only 38 days at 24 °C. PM for each additive occurs at similar thermal times, despite appearing different at conventional times. Our analysis creates a link between the efficacy of CH₄ mitigation and local temperatures, which can be related to cumulative heat (thermal time/degree-days) to establish site-specific guidance for CH₄ mitigation protocols.