Kväveförluster och energianvändning på mjölkgårdar i västra Sverige
Protecting the environment has with time grown to take a more central role in the society.
Agriculture plays an important role in the society since this sector produces our food. More
thorough research on how agriculture affects the environment is therefore motivated. This
research can be used to improve the agricultural practice from an environmental point of view.
This is something that both the farmers and the consumers can profit from.
This study aims to form the basis for creating environmental indicators for use of nitrogen and
energy on dairy farms. Twenty-three farmers in western Sweden have been interviewed about
their farms, both organic and conventional. They produce milk with different intensity, defined
as the amount of milk delivered (sold) per hectare of arable land. The farms were divided in the
following groups based on the farms way of production/intensity of production:
? Organic: farms producing milk according to KRAV4.
? Conventional Mid: farms delivering below 7500 kg ECM.
? Conventional High: farms delivering more than 7500 kg ECM/ha.
Two different perspectives have been used. In the Farm-perspective all activities within the
farm is accounted for (farm-gate method) and nitogen surpluses and losses are related to hectare
of arable land. This method is used within the Swedish advisatory project "Greppa Näringen"
today. The other perspective, the Milk-perspective, includes a life cycle inventory. Flows and
losses of nitrogen and the energy use is related to the amount of milk (1000 kg ECM) that is
delivered from the farm.
Farms in the organic group had, on average, the lowest nitrogen surplus both per hectare (79 kg
N) and per 1000 kg ECM (12,5 kg N). The main cause is probably a lower input of nitrogen into
the farm compared with the conventional farms. In the Mid-group the nitrogen surplus per
hectare was somewhat lower compared with the High-group, 122 kg N/ha and 166 kg N/ha
respectively. The relationship was the opposite between the conventional groups in the other
Milk-perspective. The surplus was 19,3 kg N/1000 kg ECM in the Mid-group and 15,0 kg
N/1000 kg ECM for the High group.
Due to higher livestock density on the farms in the High-group the calculated loss of nitrogen as
ammonia (NH3-N) and nitrous oxide (N2O-N) were the highest per hectare arable land. The
organic farms had, in the Milk-perspective, the highest calculated losses of nitrogen within the
farm. A possible reason for this is the lower amount of milk delivered/sold per cow, i.e less
tonnes of milk to divide the nitrogen losses with.
The rate of explanation explains how much of the nitrogen surplus that can be found as
calculated losses on the farm level. If, for example, the farm has a nitrogen surplus of 100 kg
N/ha and the calculated nitrogen losses are 60 kg N/ha, the rate of explanation becomes 60 %.
A relatively low input of nitrogen and therefore low nitrogen surplus among the organic farms
gives a higher rate of explanation if compared with conventional farms. Since the results are
based on calculations with models it is possible that the losses of nitrogen may have been
underestimated on the conventional farms and/or overestimated on the organic farms.
Through production of fertiliser and concentrate feed, losses of nitrogen (primarily as nitrate
and nitrous oxide) and use of energy take place outside the farm and this is included in the Milkperspective.
Conventional farms had a higher share of the energy use and loss of nitrous oxide
outside the farm compared with the organic farms. A result based on the use of mineral fertiliser
and more purchased fodder on the conventional farms.
The total calculated emission of nitrogen as nitrate and ammonia in the lifecycle were highest
on the organic farms, 6,5 kg NO3-N/1000 kg ECM and 4,6 kg NH3-N/1000 kg ECM
respectively. A possible cause is the lower delivery of milk per cow compared with the
conventional farms. The losses of nitrogen that occur within the farm are calculated with
models. The Mid-group had the highest emission of nitrogen as nitrous oxide per tonne milk,
but the differences between groups were small.
Nitrogen losses as nitrate outside the farms boundaries represented 32 % of the total calculated
losses in the High-group. For the Mid-group the share was 23 % and for the organic group 27
%. The share being higher for the organic group compared with the Mid-group can be due to the
composition of the purchased fodder.
Energy use, per kilo milk, within the farm (via diesel and electricity) was higher for the organic
farms. A possible cause may be that less milk is delivered/sold per cow in relation to the
produced amount. The organic farms also produce a larger share of the fodder on the farm, this
demands more energy. More milk stays within the borders of the organic farms due to the fact
that calves are to be fed with whole milk to the age of twelve weeks at least. The differences in
energy use within the farm were small between the Mid- and High-group.
The total use of energy in the lifecycle was 2,10 MJ/kg milk for the organic group, which was
23 % lower compared with the Mid-group (2,73 MJ/kg milk). The High-group had an energy
cost of 2,60 MJ/kg milk.
If the energy use instead is expressed per cow and year the value for the organic group became
16,1 GJ/cow and year, 22,6 GJ/cow and year for the Mid-group and for the High-group 23,9
GJ/cow and year. Although the High-group had a lower usage per kilo milk delivered to the
dairy compared with the Mid-group the value per cow became higher. This may be due to the
higher delivery of milk per cow in the group Conventional High.