Monitoring GHG from manure stores on organic and conventional dairy farms

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 (SF6) 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 42.3 g C m(-3) d(-1), respectively, with the mean CH4 emission rates of 35 and 26 g C m(-3) d(-1). On both farms, nitrous oxide emissions were close to zero. Methane emissions measured from the indoor organic FYM in summer were 17.1 g C m(-3) d(-1) and the nitrous oxide emission was 411 mg N m(-3) d(-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 CH4, CO2 and NH3 were, respectively, 14.9 g C m(-3) d(-1), 12.9 g C m(-3) d(-1) and 18.6 mg NH3 m(-2) d(-1) of slurry in February and 12.0 g C m(-3) d(-1), 9.5 g C m(-3) d(-1) and 335 mg NH3 m(-2) d(-1) slurry in March. No nitrous oxide production could be measured. (c) 2005 Elsevier B.V. All rights reserved