Seaweed fertiliser

[1][3] On a broader socio-ecological scale, seaweed aquaculture and fertilizer development have significant roles in biogeochemical nutrient cycling through carbon storage and the uptake of nitrogen and phosphorus.

While the seaweed fertilizer industry is still in its infancy, it holds significant potential for sustainable economic development as well as the reduction of nutrient runoff in coastal systems.

[7] The first written record of agricultural use seaweed was from ancient Greek and Roman civilizations in the 2nd century, where foraged beach castings were used to feed livestock and wrap plant roots for preservation.

Historical records and archaeological evidence of seaweed fertilizer use in the coastal Atlantic are vast and scattered, ranging from Scandinavia to Portugal, from the neolithic period through the 20th century.

[16][20][18][5][21] Most details of seaweed fertilizer use come from the British Isles, Channel Islands, Normandy and Brittany (France), where a variety of application techniques were used over the centuries, and some continue to this day.

Ireland has a long history (12th century) of harvesting seaweed for fertilizing nutrient-poor post glacial soils using composted manure as enrichment and the increased agricultural productivity allowed the Irish population to grow substantially.

[16] The Channel Islands (12th century) used a dried blend of red and brown seaweeds, called "Vraic" or "wrack", to spread over potato fields during the winter months to enrich before planting the crop in the spring.

[16] Similarly, coastal people in Normandy and Brittany have been collecting "wrack" using wood rakes since the neolithic period, though the fertilizer composition originally included all marine debris that washed ashore.

This ‘lazy bed’ method afforded minimal crop rotation and allowed rugged landscape and acidic soils to be farmed, where plant growth was otherwise unsuitable.

[22][18] The industry developed out of demand for ashed soda, or potash, which was used to create glass and soap, and led to shortages for agricultural applications in traditional coastal communities.

[10][32][9][31] Additionally, seaweed fertilizer can be produced using by-products from other industries or raw materials that are unsuitable for human consumption, such as rotting or infected biomass or biowaste products from carrageenan processing methods.

[7][6][8] Seaweeds have been consumed by humans for centuries because they have excellent nutritional profiles, contain minerals, trace elements, amino acids, and vitamins,[7] and are high in fiber and low in calories.

[1] Seaweed fertilizer can be used as a crude addition to soil as mulch, composted to break down the hardy raw material, or dried and pulverized to make the nutrients more bioavailable to plant roots.

[40] Since seaweed extract has chelating properties that maintain trace metal ions bioavailability to plants, additional micronutrients are often added to solution to increase the fertilization benefit to specific crops.

[5][45][55] Seaweeds have received significant attention for their potential to mitigate eutrophication in coastal ecosystems through nutrient uptake during primary production in integrated multi-trophic aquaculture (IMTA).

[44][51] The bioremediation potential of seaweeds depends, in part, on their growth rate which is controlled by numerous factors including water movement, light, desiccation, temperature, salinity, life stage, and age class.

[57] Bioremediation practices have been widely used due to their cost-effective ability to reduce excess nutrients in coastal ecosystems leading to a decrease in harmful algal blooms and an oxygenation of the water column.

[58] The application of seaweed fertilizers can also result in enhanced tolerance to abiotic stressors that generally inhibit crop growth and yield such as low moisture, high salinity, and freezing temperatures.

[3] Research has also demonstrated that wheat plants treated with seaweed extracts have accumulated key osmoprotectants such as proline, other amino acids, and total protein.

[67] While this is a new field of research, current data shows that targeted breeding of seaweeds may result in biochars that can be tailored to different types of soil and crops.

[68] In addition, several species of seaweed appear to hinder the early growth and development of numerous detrimental insects, including Sargassum swartzii, Padina pavonica, and Caulerpa denticulata.

[69][70] Many DNA sequencing and omics-based approaches, combined with greenhouse experiments, have been used to characterize microbial responses to seaweed fertilizer treatment on a wide variety of crops.

[71] Enzyme assays also displayed an increase in protease, polyphenol oxidase, dehydrogenase, invertase, and urease activity,[71] which was thought to be induced by microbial community alterations.

Wang et al. found that apple seedlings treated with seaweed fertilizer differed markedly in fungal diversity and species richness, when compared to no-treatment control groups.

With the use of 16S rRNA and fungal internal transcribed spacer (ITS) sequencing, Renaut et al. examined the effect of Ascophyllum nodosum extract treatment on the rhizospheres of pepper and tomato plants in greenhouses.

[80] This group analyzed plant RNA transcripts and found that the seaweed extract primed A. thaliana to defend against the fungal pathogen before its inoculation, which led to increased host survival and decreased susceptibility to infection.

[80] Fewer studies have analyzed the impact of seaweed fertilizer treatment on plant resistance to viral pathogens, however limited auspicious results have been demonstrated.

[3] It has been shown that green, brown, and red seaweeds contain polysaccharides that illicit pathogen response pathways in plants, which primes defense against viruses, along with bacteria and fungi.

[82] Another study done on tobacco plants found that sulfated fucan oligosaccharides, extracted from brown algae, induced local and systemic acquired resistance to TMV.

[83] Based on the above results, it can be stated that the application of seaweed fertilizers has considerable potential to provide broad benefits to the agricultural crops and resistance to bacterial, fungal, and viral plant pathogens.