Sargassum digestate as fertiliser in Grenada

Sammanfattning: Surges of Sargassum have become more severe and at the time of writing the largest surge yet is set to hit the Caribbean islands, affecting tourism and marine life negatively. Tourism is Grenada’s single handedly largest economic sector, which is why it is important to research the use of Sargassum. Furthermore, for its fertiliser needs, Grenada relies largely on importing inorganic fertiliser, which has become more expensive in recent years. Sargassum as feedstock for biogas digesters and utilising the digestate as fertiliser could be a viable option, but challenges include high heavy metal content and low concentration of nutrients compared to inorganic fertiliser. The aim of this project is to examine heavy metals contents in digestate derived from Sargassum and gaining knowledge about the current agricultural situation, with regards to fertiliser, through interviewing farmers and relevant political figures. The results from the heavy metal analysis of the liquid digestate showed that the concentration of both arsenic and cadmium were below the average for commercial organic fertilisers. However, further testing is considered to be required to conclude whether the product is suitable to use. Gathered from the interviews was that many farmers were concerned about the impact inorganic fertiliser had on the land, however, the choice of fertiliser was, in general heavily dependent on which type was available. Sargassum-based digestate could be viable on the island but challenges of reducing, transporting and separating heavy metals from the digestate have to be solved making it difficult for the Sargassum to be cost-effective. Furthermore, the farmers were very clear that they wanted a product which was safe to use.