Cutting food waste, improving the recycling of nitrogen in food production and new agricultural technologies are some of the methods that can be used to reduce nitrogen emissions to the environment. These are the conclusion drawn from the development of a new nitrogen budget for Denmark by scientists at Aarhus University.

To get a clearer overall picture of the sources and sinks of nitrogen, scientists from Aarhus University have developed a national nitrogen budget for Denmark for the years 1990 to 2010. The budget shows inputs and outputs of nitrogen at national level and the internal flows of nitrogen between the relevant sectors.

- By creating a nationwide picture of nitrogen consumption and emissions in Denmark it is easier to identify where efforts can be focused most efficiently to reduce nitrogen emissions to the environment. It also makes it easier to identify imbalances between inputs and outputs, says Senior Scientist Nick Hutchings from the Department of Agroecology at Aarhus University.

Over the past 25 years, a raft of environmental regulations have been introduced in Denmark to reduce nitrogen emissions to the environment, particularly from agriculture. Combined with more efficient feeding of livestock, this has led to a significant reduction in nitrogen losses from agriculture: leaching of nitrogen to the aquatic environment has been halved in the period - without a corresponding fall in production.

National nitrogen budget gives a clearer picture
By setting up a national nitrogen budget it is possible to identify the areas where efficiency savings can be made from recycling or re-use. By subsequently estimating the cross flows of nitrogen you can also take into account any interactive effects.

As an example, the Danish import of nitrogen in protein feed has risen. This is livestock numbers and therefore demand for feed has increased but the yield of feed crops has remained the same because of the restrictions in the environmental regulations in Denmark that limit the amount of nitrogen in animal manure and mineral fertilizer that can be applied to crops.

Since 1990 significant reductions in nitrogen emissions have been achieved, but agriculture is still a major contributor of nitrogen emissions to the environment.

In the agricultural sector the lowest hanging fruit have already been picked, and further reductions may be relatively expensive compared to the effect. It may therefore be worthwhile exploring other economic sectors to see if it is possible here to achieve greater reductions at lower costs, says Nick Hutchings.

The scientists based their calculations on statistical data and the latest Danish emission inventories for 1990 and 2010.

Potential for reduction
The budget can be used to discuss the potential for further reductions in nitrogen losses to the environment, including increased recycling of nitrogen between economic sectors.

There appears to be scope for efficiency savings from the re-use of nitrogen in and across sectors. This is especially true in the production and consumption of foods, where a focus area is food waste.

Another focus area is the development of technologies that can render grass suitable for the production of protein feed. Grass is good at utilising nitrogen and can be grown on nitrate-sensitive areas if combined with appropriate nitrogen fertilization, explains Nick Hutchings.

In the scientific article, the scientists suggest a number of other initiatives to reduce nitrogen emissions, including an expansion of the area under organic farming, an increased use of manure for biogas production, conversion of land that is vulnerable to nitrogen leaching to, for example, energy crop production, and the establishment of mini-wetlands.

In the transport and energy sectors a shift to electrically powered vehicles will reduce emissions of nitrogen if the production of electricity is based on non-fossil energy sources such as wind, water or sun.

Much of the nitrogen that ends up in the Danish environment originates from other countries. We therefore have a strong economic and environmental interest in cooperating with our neighbours to also reduce their nitrogen emissions, says Nick Hutchings.

The scientific article "A nitrogen budget for Denmark; developments between 1990 and 2010, and prospects for the future" has been published in Environmental Research Letters.