Development and validation of a biophysical model of enteric methane emissions from Australian beef feedlots

Abstract

Feedlot producers face considerable pressure to reduce emissions of greenhouse gases and excretion of nitrogen and phosphorus. This paper reports on the development and validation of a biophysical model to predict greenhouse gas emissions from Australian beef feedlots, specifically enteric methane emissions. The developed model was based on the current Australian methodology for greenhouse sources and sinks, with the addition of two recently developed beef cattle specific models. The model was validated using the results of published studies and compared with emissions measured using open path spectroscopy and micrometeorology from two Australian feedlots during two seasons. The best performing equations were Ellis et al. (2007) and Moe and Tyrell (1979) with Lins concordance values and 95% confidence intervals of 0.4509 (0.1018) and 0.3696 (0.1362). Average residuals were 118.6 and 98.2 g/head/day for the two best performing equations. The IPCC Tier II equation demonstrated the lowest average residual 0.6 g/head/day but also the poorest concordance (Pc 0.0657, 95% CI -0.024). This study demonstrates that the current Australian methodology for estimating enteric emissions from feedlot cattle is overestimating emissions.