NEWS
Climate impact of grass-fed
cattle overestimated, says study
Cattle that graze pasture rich in
white clover produce just half the
amount of nitrous oxide than previously
thought, according to a study
carried out by Rothamsted Research.
The findings suggest the climate impact
of grass-fed cattle herds is overestimated
and could help farming achieve
its ambition of becoming a “net-zero”
emissions industry by 2040.
Nitrous oxide is a potent greenhouse
gas that is 265 times more harmful than
carbon dioxide and thought to account
for 40% of beef supply chain emissions.
How the emissions study worked
Rhian Price
Current Address: Sutton, UK
E-mail Address: [email protected]
Reprinted From: https://bit.ly/3jM393N
Most studies of emissions from livestock
combine data from a variety of experimental
systems in addition to some estimated
values from the Intergovernmental
Panel on Climate Change (IPCC).
These figures assume all cattle urine
or faeces deposited on soils cause the
same volume of nitrogen-based emissions
irrespective of pasture type.
However, researchers at Rothamsted
created a more realistic farming scenario
by measuring emissions from one
herd using a near “closed” system,
which allowed the flow of nitrogen from
soil to forage to cattle, and back to soil
again (as deposited urine and dung) to
be monitored.
The grazing platform at Rothamsted’s
North Wyke Farm, Devon, was divided
into three grazing systems:
1. Permanent pasture (predominately
perennial ryegrass), not ploughed
for 20 years. This received inorganic
nitrogen in the form of ammonia
nitrate, applied three times during
the grazing season at 40kg N/ha.
2. Perennial ryegrass containing a
high-sugar grass (AberMagic). Also
received inorganic nitrogen, as
above.
3. A high-sugar grass and clover mix
where no nitrogen was applied.
Weaned cattle were randomly assigned
to each system. Urine and dung samples
were collected from the cattle and
applied to areas to reflect simulated
grazing with grass also cut twice.
Nitrous oxide emissions were measured
using static gas chambers installed in
the soil, with samples collected over a
six-month period (April to September
2017). Five treatments were analysed:
cattle urine, dung, synthetic urine and
synthetic fertiliser.
Figure 1: White clover pasture
Grassroots Vol 20 No 3 September 2020
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