The following recent papers can be relevant:

http://dx.doi.org/10.1016/j.jenvman.2020.111193

http://dx.doi.org/10.1088/1742-6596/1823/1/012028

@ Navindra, I think it is appropriate for crop and seedling production. Because, seaweeds are not only a source of macro- and micronutrients (e.g., Mg, Sr, B and Fe), but also contain amino acids, vitamins as well as plant-growth promoting substances including cytokines, auxins, and abscisic acid . These characteristics make seaweed biomass an attractive resource for composting. You may use alone or enrich with N and P. In India, we have a industry "Aquaagri", they are manufacturing efficient biofertilizer from seaweeds.

Seaweeds also contain lots of chloride and trace elements that they have accumulated fro seawater, e.g., As, Cd, I. So use with care on food crops!!

Thank you Paul, any research work on As accumulation in seaweeds?

Seaweeds are not only a source of macro- and micronutrients but also contain amino acids, vitamins as well as plant-growth promoting substances including cytokines, auxins, and abscisic acid. These characteristics make seaweed biomass an attractive resource for composting. As a fertilizer, seaweed can provide a natural form of potash (soluble potassium). Non-synthetic forms of seafood products are permitted in organic crop production. Extraction or other processing using water, heat, pressure, or non-synthetic materials is permitted. If don't have beds that are suitable for such methods, add the seaweed to compost, or compost it on its own. Once broken down, it's the magic ingredient for growing thin-skinned new potatoes, as well as for top-dressing pots, where it will act as mulch while continuing to break down. Seaweed has been used as a soil improver for centuries, particularly in coastal areas. Seaweed contains several useful plant nutrients, including nitrogen, potassium, phosphate and magnesium. Microalgae can be cultivated to have a high protein and oil content, for which can be used to produce either biofuels or animal feeds, or both. In addition, microalgal biomass, which is rich in micronutrients, is already used for dietary supplements to advance human health. Life-cycle assessments show that growing algae is a lot more sustainable than growing plants. Compared to other sources of protein they also require far fewer fertilizers or chemicals for crop protection. Plus they emit a lot less greenhouse gases. Microalgae as bio-fertilizer. Many aspects of microalgae make them a potential entity for bio-fertilizer, such as nitrogen fixation, production of various substances for plant growth promotion, and improvement of soil physical properties. Microalgae as bio-fertilizer. Many aspects of microalgae make them a potential entity for bio-fertilizer, such as nitrogen fixation, production of various substances for plant growth promotion, and improvement of soil physical properties.