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 from seaweed (rich in potassium (K), magnesium and sulphur) and fishbones (rich in nitrogen (N), phosphorus (P) and calcium) as fertilisers. In a pot experiment with ryegrass (11 treatments, 4 replicates, 5 harvests), high yields were produced with fishbones, and the short-term N availability was much higher than for mineral N fertiliser. The same result was confirmed in a field experiment with dried poultry manure as control treatment (1 fertilisation level, 5 fertilisers, 4 replicates, random block design), and an outdoor pot experiment (2 fertilisation levels, 5 fertilisers, 4 replicates, random block design). 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 products. Excess P in the fishbones may cause eutrophication of this fertiliser is applied to cover N demands of the crop. Research is needed to make a well-balanced commercial fertiliser.