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  Manure major source of greenhouse gas
A new study has found manure is a major contributor to rising nitrous oxide levels since the beginning of last century.

The research, published in today's edition of Nature Geoscience, adds to the growing debate over how best to estimate the increase in human induced nitrous oxide (N2O) levels since the industrial revolution.

Soil scientist and study author Dr Eric Davidson, of the Woods Hole Research Centre in Massachusetts, says the findings have important implications for N2O mitigation strategies.

N2O, a potent greenhouse gas, is produced both naturally and by human activities such as primarily agriculture.

Davidson says past studies have focused mainly on the contribution nitrogen fertilisers made to increasing N2O levels.

"[Fertilisers] are extremely important, but that's only part of the story," says Davidson.

He says nitrous oxide levels started increasing in the late 19th century "long before we started using nitrogen fertilisers in the 1960's."
'Double whammy'

Davidson realised there was another source not being accounted for.

Using historical records of fertiliser and manure production, Davidson was able to account for nitrous oxide levels in the atmosphere from 1860 to 2005.

"Manure production was, and presumably still is today, an important source of [N2O]," he says.

Davidson says as meat consumption continues to increase this will become a growing problem.

"The more we choose a carnivorous diet, as more and more people around the world are, there will be more demand to divert food crops to animal feed."

Davidson says the combination of increased fertiliser use for animal feed and the increase in manure is a "double whammy" for N2O levels.

"More attention should be paid on how to dispose of manure from livestock operations," he says.
Ozone effected

Davidson's study comes just days after scientists from the National Oceanic and Atmospheric Administration released a report into nitrous oxide and its effect on the environment.

They found nitrous oxide has become the main human-produced substance damaging the planet's protective ozone layer and is likely to remain so throughout the century.

"Nitrous oxide emission currently is the single most important ozone-depleting substance emission and is expected to remain the largest throughout the 21st century," the scientists wrote in the journal Science.

Scientists have called for tighter limits on N2O emissions, as it would be a "win-win for both ozone and climate."
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