Better manure management can reduce eutrophication

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A unique holistic approach to manure management

Agriculture has access to almost twice as much nutrients compared to what is needed by the crops. By mapping the surpluses, Baltic Eye researchers Annika Svanbäck and Michelle McCrackin hope to be able to help reduce nutrient leaching from agriculture to the Baltic Sea.

Text: Henrik Hamrén

- Enormous amounts of manure is produced in the Baltic Sea region every year. If we took advantage of the nutrients more efficiently, the use of fertilizers would be reduced significantly, says Michelle McCrackin.

Along with a dozen researchers from other universities, she and Baltic Eye colleague Annika Svanbäck implement a unique holistic approach to fertilizer use in the entire catchment area.

- We calculate how much nutrients each area contain - the amount of manure produced and how much fertilizer is used. We then compare this with the estimated amount taken up by the crops. We hereby obtain a net for each specific area around the Baltic Sea, says Annika Svanbäck.

Based on the calculations a unique nutrient map of the entire river basin is created, which shows the land areas that have the greatest nutrient surpluses.

- Agriculture around the Baltic Sea is subject to very different conditions. The detailed perspective is therefor fundamental. It makes it easier to tailor effective measures for individual areas, says Annika Svanbäck.

The mapping of the entire catchment area is on a rough regional scale.

- If we know which regions in different countries that have large surpluses, it makes it possible to then look in more detail at these areas and what could be done to reduce this nutrient surplus, says Annika Svanbäck.

Far between animals and fields

The map of the entire catchment area is not yet complete. Among other things, the scientists are still waiting for data from Russia and Belarus. But the preliminary results are clear:

Calculated on average there are almost twice as much nutrients in manure and fertilizer compared to what the crops take up.

In Denmark, for instance, which has a very high meat production, enough manure is produced to supply virtually all of the country's crop production with nutrients. Yet, each year Danish agriculture import large amounts of fertilizer.

- The main reasons that manure is not used more efficiently is that fertilizers are easier to handle and that there are often large distances between the fields where crops are grown and the farms where animals produce manure, says Annika Svanbäck.

Contribute to eutrophication

Animal manure contains a lot of fluid and is heavy and expensive to transport. There are modern technologies for drying manure and make it more manageable, however such machines are a great investment and represent high operating costs for the individual farmer.

- On crop farms, it is usually easier and cheaper to buy fertilizer instead of using manure, says Annika Svanbäck.

The total amount of available nutrients in manure and fertilizer greatly exceed the amount of nutrients needed for crop production, and thus likely contributes to the eutrophication of the Baltic Sea.

- In areas with high nutrient surpluses, it is reasonable to assume that the amount of nutrients reaching the sea are higher compared to areas without excess, as has also been shown by previous research, says Annika Svanbäck.

Supporting decision makers

Just over 18 per cent (approximately 305 000 square kilometers) of the land surface in the Baltic Sea catchment area is farmland. Every year fields are fertilized with a total of 3.5 million tons of nitrogen and 700 000 tonnes of phosphorus respectively. Nearly half of this comes from manure, the rest from commercial fertilizers.

Recent research estimates that of the annual applied nutrients to the Baltic Sea from land, 17 per cent of all nitrogen and 12 per cent of phosphorus is derived from manure.

- A first rough estimate shows that a ten per cent improvement, if fertilizers are replaced with manure, would reduce the annual nutrient supply to the Baltic Sea with 40 000 tonnes of nitrogen and 1,000 tons of phosphorus, says Michelle McCrackin.

According to her, the main aim of the project is to create a holistic picture, which contributes to better management of nutrients in agriculture throughout the region.

- We hope to give policy makers a good support for effective actions, which ultimately leads to reduced eutrophication in the Baltic Sea.

Michelle McCrackin


Aniika Svanbäck

Annika Svanbäck



Henrik Hamrén

science journalist