Nitrogen and Energy Utilization on Conventional and Organic Dairy Farms in Norway

Summary in the original language of the document

To improve environmental sustainability it is important that all sectors in a society contribute to improving the utilization of inputs as energy and nutrients. In Norway, dairy farming contributes with an important share to the added value from the agricultural sector, although there is little information available about utilization of energy and nitrogen (N). Many results on sustainability have been published on dairy farming. However, due to Norway’s Nordic climatic conditions, mountainous and rugged topography and an agricultural policy that can design its own prices and subsidies, results from other countries are hardly representative for Norwegian conditions. To bridge this gap, the objective of this study was to analyse if the utilisation of nitrogen and energy in dairy farming in Norway can be improved to strengthen its environmental sustainability. Data were collected from 2010 to 2012 on 10 conventional and 10 organic farms in a region in central Norway with dairy farming as the main enterprise. The farms varied in area, number of dairy cows and milk yield. For nitrogen, a farm gate balance was applied and supplemented with nitrogen fixation by clover and atmospheric N-deposition. The total farm area was broken down into three categories: dairy farm area utilized directly by the farm, off-farm area needed to produce imported roughages and concentrates, and free rangeland that only can be used for grazing. To analyse the utilization of nitrogen and energy, comparable indicators and two functional units are introduced. The use of inputs is analysed by a lifecycle assessment from cradle to farm gate. The functional units for nitrogen and energy are, respectively, 1 kg N for human consumption, with N as important component of protein, and 1 MJ of metabolizable energy in delivered milk and meat gain of the cattle herd. Thus, the input of nitrogen and energy can be measured in the same unit as the corresponding functional unit, and utilisation can be expressed as intensities. Intensities are the amount of input needed to produce one functional unit and are dimensionless. For the farm they are calculated by dividing the input (measured as kg N or MJ embodied energy needed for production) by the output (measured respectively as kg N or MJ metabolizable energy in delivered milk and meat gain). Different intensities are calculated, depending on which inputs are included, e.g. including nitrogen fixated by clover or not or embodied energy from buildings or not. Embodied energy is the sum of all fossil and renewable energy, required to produce an input. Man-power and solar radiation are not included.
The N-inputs per functional unit on all 20 farms are presented in a bar graph, visualising the contribution of the inputs to the N-intensities. N-intensities on organic dairy farms vary between 1.9 and 4.2, compared to a variation on conventional farms ranging from 3.5 to 7.3. A linear regression demonstrates that the N-intensity on purchased N and the off-farm N- surplus on conventional farms decreases with increasing milk yield, while the intensities on organic farms were lower, regardless of whether milk yields were high or low. Of an increased N-input on purchase, on average only 11 % is utilised as output, resulting in increased nitrogen surplus per area. Different variables are tested for correlation with their influence on the N-intensities. A model for all 20 farms is developed, showing that the N- intensity on purchased inputs decreases with an increasing feed-derived share of the entire N-import by purchase and with decreasing N-fertiliser use per area. It is concluded that N- intensities are suitable for quantifying the utilization of N and the share of different inputs to the N-intensities and easily comparing farms. Enabling the inclusion of embodied energy from agricultural buildings with a lower workload than a mass material calculation requires, the building construction approach is introduced. The agricultural buildings on all farms were registered and the material layers of the key building elements was described. The area of each building element was multiplied by the amount of embodied energy per square meter and the results for all elements summed up for each building.
On average for the 20 barns, the value of embodied energy in the envelope per cow-place and year was about 2,700 MJ, varying from 750 to 3,400 MJ. The results show that square meter area per cow-place, use of concrete in walls and insulation in concrete walls are the variables that contribute significantly to increasing the amount of embodied energy. It is highlighted that by choosing a design that requires less material and materials with a low amount of embodied energy, the amount of embodied energy in buildings can be significantly reduced.
Furthermore, the variation in energy utilisation and possible improvements are analysed. Comparable to nitrogen input, an increasing production of metabolizable energy per hectare can be explained by an increased input of embodied energy from all inputs, with a utilisation of nearly 40 % on conventional and nearly 50 % on organic farms. Energy intensities calculated were significantly lower on organic than on conventional farms.
The contribution of embodied energy from the different inputs to the energy intensities is shown for all 20 farms. Machinery and buildings are found to contribute with an average of 19 % on the conventional farms and 29 % on the organic farms to energy intensity on all inputs, with a variation of 15 % to 43 % for all 20 farms. Calculated on all inputs, the energy intensities on conventional farms varied from 2.1 to 3.3 and on organic farms from 1.6 to 2.9. On conventional farms, the energy intensities decreased with increasing milk yield, while organic farms produced without a significant influence from milk yield. These findings are comparable to this study’s finding on the influence on milk yield on nitrogen intensity. On organic farms, there was a bigger influence from machinery and buildings on energy intensity than on conventional farms, especially on those organic farms with low milk yields. The influence of different variables on the energy intensities is analysed. This is done separately for conventional and organic farms because different variables are found to be important both in regard of conventional or organic production, and depending on if only energy from purchased inputs or also energy embodied in infrastructure is included. The energy intensity on conventional farms is positively correlated to tractorweight per area and nitrogen intensity on purchased inputs. On organic farms the energy intensity is positively correlated with the ground-floor area per cow in the barn and negatively correlated with liveweight per cow and share of nitrogen fixated by clover of total nitrogen input by purchase. Due to the important contribution from machinery and buildings to the overall energy consumption in dairy farming it is highly recommended to include them in energy-analyses and to find solutions to improve their utilisation.
Comparing nitrogen, energy, area, and economic intensities underlines that on conventional farms, nitrogen, energy, and area intensities are positively correlated, while on organic farms only energy and area intensities are positively correlated. When looking for more environmentally sustainable solutions for dairy farming, it is an advantage that some intensities are positively correlated and not negatively correlated to the economic outcome. Among the 20 farms, three conventional and three organic farms performed better than average within their respective group in regard to all four intensities.
The organic dairy farms in this study produce milk and meat on average with lower nitrogen and energy intensities and lower nitrogen surplus per area than the studied conventional farms. Intensities are found to be superior to efficiencies since they not only display the utilisation of nitrogen and energy, but also allow displaying the share of each input. This feature is important for communicating with farmers and finding solutions aimed at reducing intensities. It is concluded that the utilisation of nitrogen and energy can be improved, and different solutions are recommend for conventional and organic farms, respectively. Presumably, the best results can be obtained by conducting farm-specific analyses for finding solutions for reduced intensities and by developing agricultural policies that support a better utilisation of nitrogen and energy in the production of milk and meat.