Seaweed fertiliser
Seaweed fertiliser is organic fertilizer made from seaweed that is used in agriculture to increase soil fertility and plant growth. The use of seaweed fertilizer dates back to antiquity and has a broad array of benefits for the soils.
Seaweed fertilizer can be applied in a number of different forms, including refined liquid extracts and dried, pulverized organic material. Through its composition of various bioactive molecules, seaweed functions as a strong soil conditioner, bio-remediator, and biological pest control, with each seaweed phylum offering various benefits to soil and crop health. These benefits can include increased tolerance to abiotic stressors, improved soil texture and water retention, and reduced occurrence of diseases.
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. Seaweed fertilizer application to soils can also alter the structure and function of microbial communities. Seaweed aquaculture has the potential to yield ecosystem services by providing a source of nutrition to human communities and a mechanism for improving water quality in natural systems and aquaculture operations.
The rising popularity of organic farming practices is drawing increased attention towards the various applications of seaweed-derived fertilizers and soil additives. 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. There are however ongoing challenges associated with the use and production of seaweed fertilizer including the spread of diseases and invasive species, the risk of heavy-metal accumulation, and the efficiency and refinement of production methods.
Nomenclature and taxonomy
"Seaweed" is one of the common names given to multicellular macroalgae, such as green algae, brown algae, and red algae. The term, seaweed is sometimes used to refer to microalgae and plants as well. Seaweeds are typically benthic organisms which have a structure called a holdfast, that keeps them anchored to the sea floor; they also have a stipe, otherwise known as a stem, and blade-shaped foliage. Sargassum seaweed is one exception to this anatomy and function, as it does not attach to the benthic environment. The color of seaweeds generally follows depth/light, with green seaweeds, brown seaweeds, and red seaweeds corresponding to shallow, moderate, and deeper waters respectively; red seaweeds are sometimes found up to 30 meters in depth. The smallest seaweeds grow only a few millimeters in height, while the largest seaweeds can grow up to 50 meters in height. There are an estimated 1,800 green, 1,800 brown, and 6,200 red seaweed species in existence. Brown seaweeds are generally known as kelp, but are also known by other common names such as rockweed and wracks. Red seaweeds are the most diverse group of seaweed, and along with green seaweeds, are most closely related to terrestrial plants, whereas brown seaweeds are the most distantly related to terrestrial plants. Seaweeds are found extensively in shallow natural environments, and farmed both in the ocean and in land-based aquaculture operations. Most brown seaweeds that are found in the wild are from the genera Laminaria, Undaria, Hizikia, whereas most brown seaweeds that are farmed for uses such as fertilizer and heavy metal indication, are from the species Ascophyllum, Ecklonia, Fucus, Sargassum. Green seaweeds that are used as bioindicators, for heavy metal indication for example, are from the genera Ulva and Enteromorpha. Red seaweed from the genus Poryphora, is commonly used for human food.History
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. However, stable isotope analysis of prehistoric sheep teeth in Orkney indicate that early peoples used seaweed as livestock fodder over 5,000 years ago, and researchers speculate that foraged seaweed was also used as fertilizer because ashed remnants of seaweed were found in archeological sites. Such agricultural techniques might have been key to the survival of early settlements in Scotland.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. Most details of seaweed fertilizer use come from the British Isles, Channel Islands, Normandy and Brittany, where a variety of application techniques were used over the centuries, and some continue to this day. Ireland has a long history 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. The Channel Islands 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. 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. In 17th–19th century Scotland, Fucus spp. were cultivated by placing rocky substrate in the intertidal zones to encourage seaweed settlement. The seaweed biomass was then used in composted trenches, where crops were grown directly in the sandy fertilizer mixture. This 'lazy bed' method afforded minimal crop rotation and allowed rugged landscape and acidic soils to be farmed, where plant growth was otherwise unsuitable. The high value of seaweed in these regions caused political disputes over harvesting rights and in Ireland such rights were established before the country itself. These early applications of seaweed fertilizer were limited to coastlines, where the macroalgae could be harvested from the intertidal or collected after a storm washed it to shore. However, dried wrack mixtures or ashed 'fucus' potash could be transported further inland because it weighs less than wet seaweed.
Seaweed fertilizer spread inland when a kelp industry developed in Scotland, Norway, and Brittany in the 18th and 19th century. 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. Potash is a water-soluble potassium rich concentrate made from plant matter, so it was also exported as a fertilizer. Coastal communities in the seaweed industry both expanded and struggled to keep up with the demand. Early commercial kelp export in Scotland devastated traditional agriculture in the region because intensive labor was needed during the seaweed growing season to harvest and process the kelp, which led to a labor transition from farming to kelp processing. Additionally, exploitation of kelp resources for potash production left little kelp behind for local fertilizer and coastal land became more desirable than inland regions. The Scottish seaweed industry went through multiple boom and bust cycles, employing 10,000 families and producing 3,000 tonnes of ash per year during its peak. The export price of kelp ash dropped in 1822, leading to a sudden emigration from the area because the crop was no longer profitable enough to support such a large industry. Kelp exploitation and toxic ash processing caused ecological and economic damage in Orkney and left many people sick and blinded. The kelp industry picked up again for iodine production in 1845, and alginate production in the early 1900s, which reinvigorated kelp harvest.
Global production of seaweed fertilizer largely phased out when chemical fertilizers were developed in the 1920s, due to the cheaper production cost. Chemical fertilizers revolutionized the agriculture industry and allowed the human population to grow far beyond the limits of traditional food production methods. Synthetic fertilizers are still the predominant global source for commercial agricultural applications due to the cheap cost of production and widespread access. However, small scale organic farmers and coastal communities continued traditional seaweed techniques in regions with a rich seaweed history. The first industrial kelp liquid fertilizer, Maxicrop, was created by Reginald Milton in 1947. The creation of liquid fertilizer has allowed for more widespread application of seaweed-derived fertilizer to inland regions and sparked a growing agronomic interest in seaweed for a variety of agricultural applications, including foliage spray, biostimulants, and soil conditioning. Interestingly, the historic rise of seaweed aquaculture did not align with fertilizer production because the European countries that produce seaweed fertilizer haven't developed a significant aquaculture industry; seaweed farming is also currently dominated by China and Indonesia, where the crop is grown for food and other lucrative uses.