Harvesting our fertilisers from the sea - an approach to close the nutrient gaps in organic farming

Summary

Organic production in Europe is currently dependent on the input of fertilisers derived from conventional agriculture, such as farmyard manure, slurry and fertilisers derived from slaugther residues. A significant part of the nutrient flows in our food systems goes in one direction, from land to sea, via sewage and leaching. Harvesting marine organisms for fertilisation, or utilising residual materials e.g. from fish industry as fertilisers, may close such nutrient gaps and promote active cycling of nutrients. At NORSØK, we are studying the use of algae fibre (rich in potassium (K), magnesium and sulphur) and fishbones (rich in nitrogen (N) and phosphorus (P)) as fertilisers. High yields were produced with fishbones, and the short-term N availablity was much higher than for mineral N fertiliser or dried poultry manure. Plants with a long period of nutrient uptake benefited from algae fertiliser. However, seaweeds contain significant amounts of arsenic (As), and easily available K may impact a balanced mineral content in the food or feed product. Excess P in the fishbones may cause eutrophication if this fertiliser is applied to cover the N demands of the crop. Research is needed to make a well balanced fertiliser.