Kväveförluster och energianvändning på mjölkgårdar i västra Sverige

Abstract: 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.