Monitoring GHG from manure stores on organic and conventional dairy farms [An article from: Agriculture, Ecosystems and Environment]
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Description: Organic farming methods are claimed to be more
environmentally friendly than conventional methods and the EU MIDAIR project had an overall aim to
compare emissions from organic dairy farming with conventional methods of milk production. Manure
stores are the second largest source of methane emissions (after enteric fermentation) on European
dairy farming. The aim of this project was to measure green house gas (GHG) emissions from manures
in covered and uncovered slurry stores and farm yard manure (FYM) heaps. The chosen method for
measuring these emissions was the tracer ratio method, using sulphur hexafluoride (SF"6) as the
tracer gas, the limitations of this method prevented successful measurements being made on some of
the stores and a modified method was used on the covered stores. The difference in concentration of
the upwind and downwind samples and interfering sources were limiting factors. FYM emission
measurements were successful only when the manure was stored indoors. Methane emissions were
successfully measured over a 12 month period from the uncovered slurry stores. Emission rates from
the uncovered slurry stores on the conventional farm and the organic farm ranged from 14.4 to 49.6
and from 12.4 to 42.3g C m^-^3d^-^1, respectively, with the mean CH"4 emission rates of 35 and 26g C
m^-^3d^-^1. On both farms, nitrous oxide emissions were close to zero. Methane emissions measured
from the indoor organic FYM in summer were 17.1g C m^-^3d^-^1 and the nitrous oxide emission was
411mg N m^-^3d^-^1. The covered slurry stores were in such close proximity to other GHG sources that
the tracer ratio method was unsuitable and the air-injection method was adopted. The measured
emissions from covered slurry stores of CH"4, CO"2 and NH"3 were, respectively, 14.9g C m^-^3d^-^1,
12.9g C m^-^3d^-^1 and 18.6mg NH"3m^-^2d^-^1 of slurry in February and 12.0g C m^-^3d^-^1, 9.5g C
m^-^3d^-^1 and 335mg NH"3m^-^2d^-^1 slurry in March. No nitrous oxide production could be measured.
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