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Compost can turn agricultural soils into a carbon sink, thus protecting
against climate change

Special issue of Waste Management and Research published today by SAGE
Los Angeles, London, New Delhi, and Singapore (25 February, 2008) *
Applying organic fertilizers, such as those resulting from composting,
to agricultural land could increase the amount of carbon stored in these
soils and contribute significantly to the reduction of greenhouse gas
emissions, according to new research published in a special issue of
Waste Management & Research (Special issue published today by SAGE).
Carbon sequestration in soil has been recognized by the
Intergovernmental Panel on Climate Change and the European Commission as
one of the possible measures through which greenhouse gas emissions can
be mitigated.

One estimate of the potential value of this approach * which assumed
that 20% of the surface of agricultural land in the EU could be used as
a sink for carbon * suggested it could constitute about 8.6% of the
total EU emission-reduction objective.
³An increase of just 0.15% in organic carbon in arable soils in a
country like Italy would effectively imply the sequestration of the same
amount of carbon within soil that is currently released into the
atmosphere in a period of one year through the use of fossil fuels,²
write Enzo Favoino and Dominic Hogg, authors of the paper.
³Furthermore, increasing organic matter in soils may cause other
greenhouse gas-saving effects, such as improved workability of soils,
better water retention, less production and use of mineral fertilizers
and pesticides, and reduced release of nitrous oxide.²
However, capitalizing on this potential climate-change mitigation
measure is not a simple task. The issue is complicated by the fact that
industrial farming techniques mean agriculture is actually depleting
carbon from soil, thus reducing its capacity to act as a carbon sink.
According to Hogg and Favoino, this loss of carbon sink capacity is not
permanent. Composting can contribute in a positive way to the twin
objectives of restoring soil quality and sequestering carbon in soils.
Applications of organic matter (in the form of organic fertilizers) can
lead either to a build-up of soil organic carbon over time, or a
reduction in the rate at which organic matter is depleted from soils. In
either case, the overall quantity of organic matter in soils will be
higher than using no organic fertilizer.
³What organic fertilizers can do is reverse the decline in soil organic
matter that has occurred in relatively recent decades by contributing to
the build-up in the stable organic fraction in soils, and having the
effect, in any given year, of ensuring that more carbon is held within
the soil,² they explain.
But calculating the value of this technique to climate change policies
is complicated. To refine previous calculations and to take account of
the positive and negative dynamics of carbon storage in soil, Favoino
and Hogg modelled the dynamics of compost application and build-up
balancing this with mineralization and loss through tillage.
Their results suggest that soils where manure was added have soil
organic carbon levels 1.34% higher than un-amended soils, and 1.13%
higher than soils amended with chemical fertilizers, over a 50-year
period. ³This is clearly significant given the evaluations reported
above regarding carbon being lost from soils, and the increasing amount
of carbon dioxide in the atmosphere,² they say.

###

The potential role of compost in reducing greenhouse gases by Enzo
Favoino and Dominic Hogg is published on Monday 25 February in a special
issue of Waste Management & Research, entitled Green House Gases and
Solid Waste Management. The article will be free online for two months.
The special issue will be available on SAGE Journals Online from Monday
25th February at http://wmr.sagepub.com/current.dtl.
Waste Management & Research is a peer-reviewed journal that satisfies
the growing demand for essential information that can be practically
applied by those who are responsible for the management of both
municipal and industrial waste. The journal publishes results from a
broad cross section of researchers and practitioners in the field; from
academic institutions, governments and the private sector.
SAGE is a leading international publisher of journals, books, and
electronic media for academic, educational, and professional markets.
Since 1965, SAGE has helped inform and educate a global community of
scholars, practitioners, researchers, and students spanning a wide range
of subject areas including business, humanities, social sciences, and
science, technology and medicine. An independent company, SAGE has
principal offices in Los Angeles, London, New Delhi, and Singapore.
www.sagepub.co.uk

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