Soil and grass samples were also taken
so scientists could analyse microbial activity.
What the study found
The trial found the white clover-high
sugar grass mix had the lowest urinary
nitrous oxide emissions compared with
the other two pasture types when the
effect of nitrogen fixation from clover
was removed from calculations.
Nitrous oxide is most associated with
urine, so researchers focused on this.
Results showed clover had an emission
factor of 0.44% for urine following
exclusion of fixation. This is
nearly half the amount of the most
recent IPCC figures for urine, which
estimate a factor of 0.77%.
This compared with 0.55% of nitrogen
losses from urine for the permanent
pasture and 0.76% for the high sugar
pasture, which were higher because
they also received fertiliser and the effects
of urine could not be isolated.
At field-scale, researchers also observed
lower amounts of the nitrous oxide-producing
gene in the white clover/
high-sugar grass mixed sward, which
suggests a complementary relationship
between these species.
Lead author of the study, Graham
McAuliffe, said: “Regarding white clover,
we have seen benefits on the Farm
Platform time and time again. At a system
level, including methane and carbon
dioxide, this is largely driven by
avoided nitrogen fertiliser production
White clover roots have the ability to
“fix” nitrogen from the atmosphere.
Dr McAuliffe said new models would
need to be created to estimate just how
much these new, lower values could reduce
total greenhouse gas emissions,
and more work would need to be done
to understand the relationship between
clover and high-sugar grasses, particularly
at the soil microbial level.
Helping farmers meet net-zero
Nitrous oxide emissions can account for
more than 40% of entire supply-chain
greenhouse gas emissions so, used in
calculations of the climate impact of
beef, these findings can have considerable
Atmospheric chemist, nitrous oxide
expert and co-author Laura Cardenas
added: “Although white clover is unlikely
to be a ‘silver bullet’ for agriculture’s
net-zero ambitions on its own, adopting
combinations, such as increasing
legume-inclusion in pasture compositions
and the utilisation of ‘low-carbon’
fertilisers, will be essential to maximise
farming’s national and international
contribution to a cooler planet.”
Download the full report click the full
report on the ScienceDirect website:
Grassroots Vol 20 No 3 September 2020