The climate impact of grass-fed cattle may have been exaggerated as scientists find emissions of a powerful greenhouse gas from certain types of pasture are lower than previously thought.
Researchers from Rothamsted Research found urine from animals reared on pasture where white clover grows – a plant commonly sown onto grazing land to reduce the need for additional nitrogen fertiliser – results in just over half the amount of nitrous oxide previously assumed by scientists to be released. Nitrous oxide is a potent greenhouse gas some 265 times more harmful than CO2 and can account for 40% of beef supply chain emissions.
Co-author of the study, Dr Laura Cardenas said:
Due to technical and logistical challenges, field experiments which measure losses of nitrous oxide from soils usually add livestock faeces and urine they have sourced from other farms or other parts of the farm, meaning that the emissions captured do not necessarily represent the true emissions generated by the animals consuming the pasture.”
Writing in the journal Agriculture, Ecosystems and Environment, the team report how they created a near ‘closed’ system whereby the circular flow of nitrogen from soil to forage to cattle and, ultimately, back to soil again, could be monitored.
Lead author of the study, Dr Graham McAuliffe and colleagues had previously discovered system-wide reductions of greenhouse gas emissions associated with the inclusion of white clover in pasture. This conclusion was primarily driven by a lack of need for ammonium nitrate fertiliser, whose production and application create greenhouse gases.
According to Dr Cardenas, further research is required to explain the detailed mechanisms behind the observed complementarity between white clover and high sugar grasses – but that the data points towards an effect of sowing clover on the soil’s microbes.
The evidence suggests that including white clover amongst high sugar grass decreases the abundance of microbial genes associated with nitrous oxide production compared with microbial communities observed under just high sugar grass.”
As the UK wants to achieve net-zero carbon emissions by mid-century, improving our understanding of greenhouse gas emissions and mitigation potentials has never been more important, she added.