The greenhouse gas emissions from agricultural systems contribute
significantly to the national budgets for most countries in Europe.
Measurement techniques that can identify and quantify emissions are
essential in order to improve the selection process of emission reduction
options and to enable quantification of the effect of such options.
Fast box emission measurements and mobile plume measurements were used
to evaluate greenhouse gas emissions from farm sites. The box measurement
technique was used to evaluate emissions from farmyard manure and several
other potential source areas within the farm. Significant (up to 250 g CH4 m-2
day-1and 0.4 g N2O m-2 day-1)
emissions from ditches close to stables on the farm site were found.
Plume emission measurements from
individual manure storages were performed at three sites. For a manure
storage with 1200 m3 dairy slurry in Wageningen emission
factors of 11-± 5 g CH4 m-3
manure day-1 and 14 ± 8 mg N2O
m3 manure day-1 were obtained in February 2002.
Mobile plume measurements were carried
out during 4 days at distances between 30 and 300 m downwind of 20 different
farms. Total farm emissions levels ranged from 14 to 95 kg CH4
day-1 for these sites. Expressed as emission per animal the
levels were 0.7-± 0.4 kg CH4 animal-1
day-1 for conventional farms. For three farms
that used straw bedding for the animals1.4 ± 0.2 kg CH4 animal-1
day-1 was obtained. These factors include
both respired methane and emission from manure in the stable and the
outside storages.
For a subset of these farms the CH4
emission was compared with monthly averaged model emission calculations
using FARMGHG. This model calculates imports, exports and
flows of all products through the internal chains on the farm using
daily time steps. The fit
of modelled versus measured data has a slope of 0.97 but r2=
0.27. Simple emission calculations were performed with a large set of
farms. Comparing these levels with the measurements gave a slope of
0.94 with r2 =0.77. Measurements and model emission estimates agree well on average,
for large farms within 30%. For small farms the differences can be up
to a factor of 3. CH4 emissions during winter seem to be
underestimated.