Fertilisation effects of marine-derived residual materials on agricultural crops

This final report from the project “Residual materials from marine industries as fertilisers in organic agriculture” is an example of blue-green collaboration. Such collaboration has been a strategic goal for many Norwegian research and innovation activities since the terms bioeconomy and circular economy came high on the agenda. Significant amounts of residual raw materials from marine industry are still poorly utilized. Traditionally, seaweeds and residues of fish and other sea animals were applied as feed and fertilisers along the coast of Norway, as elsewhere in coastal regions. These valuable materials should still be applied in agriculture, but the application needs to be adapted to a more professional and large-scale production. Organic agriculture aims at being selfsufficient in nutrients and other inputs for the production. A further aim is to recycle nutrients and organic matter not only inside the farm by feeding manure-producing animals, but by recycling nutrients lost from the farm by sales of products, and by runoff and emissions. The RESTOR project (2018-2022) has provided resources for establishing a significant research and developmental work on marine-derived fertilisers at the Norwegian Centre for Organic Agriculture (NORSØK). Marine derived fertilisers, especially from sustainable collection or capture of natural renewable resources, may fit well to the aims of organic agriculture. The project has tested residual materials rich in bones from industry processing white fish species (cod, saithe, longfish etc.), and residual material from chemical extraction of rockweed. The materials have been tested as fertilisers and soil amendments, with controlled trials indoor and in the field. A general result is a very rapid growth effect of fishbones in the year of application, with a residual effect in subsequent years resembling that of dried poultry manure. The algae fiber has no immediate fertiliser effect but has a significant residual growth effect. Due to the content of cadmium (Cd), algae fiber is a class II soil amendment product. This implies that it may be applied with up to 20 tons of dry matter per hectare over 10 years, according to Norwegian regulation. An amount close to this level was tested in ryegrass in 2020. The tetany ratio, which is an assessment calculated to assess the risk of tetany in ruminants based on the concentrations of potassium (K), magnesium (Mg), and calcium (Ca) in plant material applied as feed, was then well above the critical level. Hence, we recommend that the material should not be applied at a higher rate than 10 tons per hectare over 5 years (half the maximal rate for each application), to avoid excess uptake of potassium in crop plants. When applied as the single fertiliser material, both fishbones and algae fiber are unbalanced and should be blended with other materials. The project tested a mix where 30% of the nitrogen (N) was derived from algae fiber and 70% from fishbones. This fertiliser gave good yields both in the year of application, and in one or more subsequent growing seasons. With higher prices on energy, there is increased interest for alternative sources of plant nutrients which may complete existing fossil resources. Most European countries are currently dependent on importing phosphorus (P) and potassium, which is a challenge in a world with increasing levels of conflicts. Significant amounts of nutrients are found in the sea, but we still need both research and developmental work to establish value chains for marine-derived fertilisers which may complete the currently applied fertilisers in both conventional and certified organic agriculture. We also need adapted regulations for such products. A proposal for new regulation on organic fertilisers in Norway includes strict limits for arsenic (As), which may significantly hamper the utilization of seaweed material in fertilisers and for soil amendment. We need more research to assess such limit values. The R&D work with marine-derived fertilisers is well established, and continues, both at NORSØK and with other research organizations.