Norway produces large quantities of fish sludge that largely “disappears” into the sea. Researchers are now investigating how to better utilize this important resource in the future. NIBIO recently hosted a workshop on fish sludge at Fredrikstad Seafood at the mouth of the Glomma River. The workshop had about 50 participants. In addition to several researchers, representatives from both the aquaculture industry and the fertilizer industry participated. The workshop was part of the EU project SEA2LAND, which has been running since 2021. The project has 26 partners in 11 countries, including Norway and Chile. The goal is to find out how to make fertilizer based on residual products from fisheries and aquaculture.
Testing in full swing in Norway
“NIBIO is almost a world leader when it comes to research on fish sludge as fertilizer,” says researcher Bente Føreid. “In the SEA2LAND project, we have already tested several different fertilizer products in pot trials,” she says. Here in Norway, Grønn Gjødsel AS in Rakkestad has made a pelleted product from dried fish sludge. In addition, Norsk Landbruksrådgiving Nord-Norge has looked at how to mix composted fish sludge into peat-free growth media.
In summary, it can be said that fish sludge has great potential as a fertilizer. It contains a lot of phosphorus and some nitrogen, but little potassium. One challenge with fish sludge is that many of the readily soluble nutrients are lost to the water even before they can be collected. Unfortunately, it is these easily soluble nutrients that are also the most readily available to plants.
To retain as much of the nutrients as possible, it is important that the sludge is treated or stabilized in some way. Experiments so far show that too much fish sludge can be harmful to plants. It is therefore important that the sludge is mixed with other residual products and that the amount is adapted to the plants’ need for nutrients. Tests show that fish sludge stimulates plant growth to a greater extent than would be expected based on phosphorus uptake. This may mean that the sludge acts as a biostimulant,” says Føreid. However, we need to do more research to find out about these relationships. We will soon be starting field trials at five different locations in Europe,” says Føreid. The purpose is to see if the products behave in the same way in the field as they do in pot tests. Three different products will be tested in all countries. These are dried fish sludge from Grønn Gjødsel AS, as well as organic fertilizer from CATAR in France and liquid fertilizer from FERTINAGRO in Spain. Each country will also test a local product. Later in the project, the researchers will carry out model calculations and life cycle analyses.
Large amounts of fish sludge are available
“Every year, more than 600,000 tons of fish sludge are produced in Norway,” says senior advisor Gjermund Bahr at NIBIO. Most of it is produced in open cages and is difficult to collect. However, if we focus only on land-based facilities and hatcheries, we still have significant amounts of sludge available. The question is how we can utilize this resource. We want to look at the possibility of getting fish sludge approved as a fertilizer product in the EU,” says Bente Føreid. “The next step will be to get it approved for organic farming.”
The EU has recently opened up the possibility of proposing new products to be considered for inclusion in the EU’s positive list of materials that can be included in fertilizer products. We have proposed fish sludge, and we have also asked our contacts in the SEA2LAND project to suggest this.
Here in Norway, we have much more fish sludge than we can utilize. At the same time, the need for fertilizer is increasing in the rest of the world. If the regulations are put in place, we believe that Norwegian fish sludge could become an important export product in the future.