Perspectives on peak liquid manure temperature with implications for methane emissions

Abstract

Methane emissions from liquid manure storage are currently estimated with a methane conversion factor (MCF) based on manure temperature inputs or air temperatures as a substitute in the 2019 IPCC Tier 2 method. However, differences between peak manure temperature and peak air temperature (Tdiff) in warm seasons are likely to occur and result in poor estimates of MCF and methane emissions. To address this concern, this study aims to investigate the relationship between the Tdiff and ratio of manure surface area to manure volume (Rs:v) using a mechanistic model and by analyzing farm-scale measurement studies across Canada. Positive correlations between Tdiff and Rs:v were found using a modeling approach and from farm-scale results (r = 0.55, p = 0.06). Tdiff ranged from –2.2 to 2.6°C in farm-scale results mainly collected from eastern Canada. We suggest that manure volume and surface area, in addition to removal frequency, could be used to estimate Tdiff and be part of the criteria for improving manure temperature estimates, which could lead to improved estimates of MCF.