Seaweed fertiliser facts for kids

Seaweed fertilizer is a special kind of organic fertilizer made from seaweed. People use it in farming to make soil healthier and help plants grow better.

Using seaweed as fertilizer has been done for a very long time. It has many good effects on soil. You can use seaweed fertilizer in different ways. It can be a liquid extract or dried, crushed seaweed.

Seaweed has many helpful natural ingredients. These make it great for improving soil, cleaning up pollution (called bio-remediation), and even helping control pests. Different types of seaweed offer different benefits for soil and plants. For example, seaweed can help plants handle tough conditions like too little water or very cold weather. It can also make soil better at holding water and reduce plant diseases.

Growing seaweed (called aquaculture) and making seaweed fertilizer also help the environment. They play a big part in how nutrients move through nature. Seaweed can store carbon and take in nitrogen and phosphorus. When seaweed fertilizer is put on soil, it can also change the tiny living things (microbes) that live there.

Seaweed farming can also provide ecosystem services. It offers food for people and helps clean water in natural areas and farms. More and more people are interested in organic farming. This means seaweed fertilizers and soil additives are becoming more popular. The seaweed fertilizer industry is still quite new, but it has a lot of potential. It can help the economy grow in a sustainable way. It can also reduce nutrient runoff that pollutes coastal waters. However, there are still challenges. These include the risk of spreading diseases or invasive species, the build-up of heavy metals, and making production methods more efficient.

What is Seaweed?

"Seaweed" is a common name for large algae that grow in the ocean. These include green algae (Chlorophyta), brown algae (Phaeophyceae), and red algae (Rhodophyta). Sometimes, the word seaweed is also used for tiny algae or even some plants.

Most seaweeds live on the ocean floor. They have a part called a holdfast that keeps them stuck. They also have a stem-like part called a stipe and leaf-like blades. One type, Sargassum seaweed, is different because it floats and does not attach to the bottom.

The color of seaweed often depends on how deep it lives and how much light it gets. Green seaweeds usually live in shallow water. Brown seaweeds are found in moderate depths. Red seaweeds can live in deeper waters, sometimes up to 30 meters deep.

Seaweeds come in many sizes. The smallest are just a few millimeters tall. The largest can grow up to 50 meters! Scientists believe there are about 1,800 green, 1,800 brown, and 6,200 red seaweed species.

Brown seaweeds are often called kelp. They are also known as rockweed or wracks. Red seaweeds are the most diverse group. Red and green seaweeds are more closely related to land plants than brown seaweeds are.

You can find seaweeds in shallow natural areas. They are also grown on farms in the ocean and on land. Some common brown seaweeds found in the wild are Laminaria, Undaria, and Hizikia. Brown seaweeds grown for fertilizer or to check for heavy metals include Ascophyllum, Ecklonia, Fucus, and Sargassum. Green seaweeds like Ulva and Enteromorpha are used to check for heavy metals. Red seaweed from the Poryphora group is often eaten by people.

A Brief History of Seaweed Fertilizer

People have used seaweed in farming for a very long time. The first written records are from ancient Greece and Rome around 200 AD. They used seaweed washed up on beaches to feed animals and wrap plant roots to keep them fresh.

However, scientists have found even older evidence. Studies of ancient sheep teeth in the Orkney islands show that people fed seaweed to livestock over 5,000 years ago. Researchers also think seaweed was used as fertilizer back then. Burned seaweed remains have been found at old living sites. These farming methods might have been very important for early communities in Scotland to survive.

There is a lot of historical evidence of seaweed fertilizer use along the Atlantic coast. This ranges from Scandinavia to Portugal, from ancient times up to the 1900s. Most of the detailed information comes from the British Isles, Channel Islands, and parts of France (Normandy and Brittany). People there used different ways to apply seaweed over the centuries, and some methods are still used today.

Ireland has a long history, going back to the 1100s, of collecting seaweed. They used it to fertilize poor soils left after glaciers. They often mixed it with composted manure. This improved farming helped the Irish population grow a lot.

In the Channel Islands, also in the 1100s, people used a dried mix of red and brown seaweeds called "Vraic" or "wrack". They spread it on potato fields in winter to enrich the soil before planting in spring. Similarly, coastal people in Normandy and Brittany have collected "wrack" since ancient times. They used wooden rakes to gather it. Originally, this fertilizer included all marine debris that washed ashore.

In Scotland, from the 1600s to 1800s, people even grew Fucus seaweed. They placed rocks in the intertidal areas to encourage seaweed to grow. This seaweed was then used in composted trenches. Crops like potatoes, oats, wheat, and onions were grown directly in this sandy fertilizer mix. This method, called ‘lazy bed’, allowed farming in rough landscapes and acidic soils where plants usually wouldn't grow well.

Seaweed was so valuable in these areas that there were even political fights over who had the right to harvest it. In Ireland, these rights were set up even before the country itself was formed.

Early uses of seaweed fertilizer were limited to coastlines. This is where the seaweed could be collected from the shore or after storms. However, dried wrack or burned ‘fucus’ potash could be carried further inland. This is because it weighed less than wet seaweed.

Seaweed fertilizer began to spread inland when a kelp industry grew in Scotland, Norway, and Brittany in the 1700s and 1800s. This industry started because there was a high demand for burned soda, or potash. Potash was used to make glass and soap. This led to shortages of seaweed for farming in coastal areas. Potash is a water-soluble concentrate rich in potassium made from plants. So, it was also sold as a fertilizer.

Coastal communities involved in the seaweed industry grew but also struggled to meet the demand. Early commercial kelp export in Scotland harmed traditional farming. This was because a lot of work was needed to harvest and process kelp during the growing season. This caused many farmers to switch to kelp processing instead of farming. Also, using too much kelp for potash production left little for local fertilizer. Coastal land became more valuable than inland areas.

The Scottish seaweed industry had many ups and downs. At its peak, it employed 10,000 families and produced 3,000 tonnes of ash per year. The price of kelp ash dropped in 1822. This led to many people leaving the area because the crop was no longer profitable. Using too much kelp and processing the toxic ash also caused environmental and economic harm in Orkney. Many people became sick or blind. The kelp industry started up again in 1845 for iodine production. Then, in the early 1900s, it grew for alginate production (a thickening agent). This brought kelp harvesting back to life.

Global production of seaweed fertilizer mostly stopped when chemical fertilizers were invented in the 1920s. Chemical fertilizers were cheaper to make. They changed farming a lot and allowed the human population to grow far beyond what traditional food methods could support. Synthetic fertilizers are still the main type used in commercial farming today because they are cheap and easy to get.

However, small organic farmers and coastal communities continued to use traditional seaweed methods. This happened in areas with a long history of seaweed use. The first industrial liquid kelp fertilizer, Maxicrop, was created by Reginald Milton in 1947. Liquid fertilizer made it possible to use seaweed fertilizer in more places, even far from the coast. This sparked a growing interest in seaweed for many farming uses, like sprays for leaves, plant growth helpers (biostimulants), and soil conditioning.

It's interesting that the rise of seaweed aquaculture (farming) didn't happen at the same time as fertilizer production. European countries that make seaweed fertilizer haven't developed a big aquaculture industry. Today, seaweed farming is mostly done in China and Indonesia. There, seaweed is grown for food and other valuable uses.

Seaweed Farming (Aquaculture)

A satellite image of seaweed farms off the southern coast of South Korea. The dark squares in the image are fields of seaweed growing.

Modern seaweed farming, also called mariculture or aquaculture, has helped a lot with seaweed fertilizer research. It has also improved how seaweed is processed since the 1950s. People in Asian countries have grown seaweed for food for hundreds of years. Now, seaweed farming is growing fast worldwide for special uses. These include biofuel, agar (a gelling agent), cosmetics, medicine, and bioplastics.

The new farming sector for seaweed, which includes animal feed, soil additives, and agrochemicals, is still very small. It makes up less than 1% of the total value of seaweed aquaculture globally. However, interest in using seaweed for farming has grown a lot since 1950. This is because scientific research has shown how useful seaweed materials are for special farming chemicals.

People are more worried now about marine resources being used up and damaged. Also, the threats of climate change have increased global interest in sustainable solutions for ocean development, known as The Blue Economy. Seaweed aquaculture is seen as a way to create new industries and ensure food security. At the same time, it can help restore damaged ecosystems.

Unlike land crops, growing seaweed needs no land, no feed, no fertilizers, no pesticides, and no fresh water. Different seaweeds also offer various ecosystem services (which we'll talk about below). This makes seaweed popular as a bioremediation crop, meaning it helps clean up the environment.

Fertilizer plays an important role in sustainable seaweed farming. Seaweed farming can help reduce too many nutrients in the ocean. These nutrients often come from chemical fertilizer runoff from land. Using organic seaweed fertilizer on soil helps complete the nutrient cycle between land and sea.

Also, seaweed fertilizer can be made from by-products of other industries. It can also use raw materials that aren't good for human food. Examples include rotting or infected seaweed, or waste from carrageenan processing. Seaweed aquaculture is also important for supporting the seaweed fertilizer industry. It helps prevent using too much wild seaweed for commercial purposes.

However, the new seaweed farming industry faces challenges for sustainable growth. The environmental effects of harvesting and producing seaweed need to be carefully checked. This helps protect coastal communities and keep the good economic effects of using seaweed resources.

How Seaweed Helps the Environment

Seaweed farming, including for fertilizer, can make coastal habitats healthier. It can especially help with toxic algal blooms. Farmed seaweeds take up extra nutrients that come from runoff. This stops toxic algal blooms from growing, which can harm local ecosystems.

Seaweed fertilizers can also be more natural, less toxic, and less dangerous than chemical fertilizers. This depends on the type of seaweed fertilizer. Seaweeds are used in aquaculture farms to take up fish waste as nutrients. This improves water quality.

Humans use seaweeds for food, for animal feed, and as plant fertilizer. They also use them to improve the environment. People have eaten seaweeds for centuries because they are very nutritious. They contain minerals, trace elements, amino acids, and vitamins. They are also high in fiber and low in calories. Red seaweeds have the most protein, while brown seaweeds have the least. Of all red seaweeds, Porphyra is the most common type eaten by people. Brown seaweeds are very common, so they are often used for animal feed and fertilizers.

Scientists are also looking into seaweed as a possible source of sustainable biofuel. They are also studying its use in wastewater treatment. Some species can absorb and remove heavy metals and other harmful substances from water. They also generally show how clean the water is.

How Seaweed Farming Can Affect Ecosystems

Any environmental effects of using seaweed for fertilizer mostly depend on how the seaweed is harvested. Large-scale, unsustainable seaweed farming can change or displace natural habitats. This is due to the farming structures in the water and daily human activities in the area.

Seaweed is currently harvested from farms, from wild areas, and by collecting it from beaches. Harvesting wild seaweed can harm local ecosystems. This is especially true if too much is taken, which stops the seaweed from providing its natural benefits.

There is also a risk that very large seaweed farms, growing only one type of seaweed, could be set up in natural ocean floor environments. This could push out native seaweeds and seagrasses that live under the farms. Also, large industrial seaweed farming can change the natural environment where it is set up. It can change things like how much light reaches the bottom, how water moves, how much sediment builds up, and nutrient levels. This is also due to the overall stress caused by human activities.

How Seaweed Fertilizer is Made and Used

The composition of various minerals found in three different species of seaweed.

Brown seaweeds are the most common type used for fertilizer, both now and in the past. Seaweed fertilizer can be added directly to soil as mulch. It can also be composted to help the tough material break down. Or, it can be dried and crushed into a powder. This makes the nutrients easier for plant roots to take in.

Compost fertilization is a method that any small organic farm can use if they have access to seaweed. However, liquid extracts are more common for large commercial farms. Commercial production methods are often more technical than traditional ways of using raw seaweed. They use different chemical processes to get and concentrate the most helpful nutrients from seaweed.

A simple liquid fertilizer can be made by fermenting seaweed leaves in water. But in factories, this process is made faster and stronger using heat and pressure. Other ways to get liquid extracts include a gentle process with low-temperature grinding to mix fine particles in water. Another way is heating the raw material with alkaline sodium or potassium to extract nutrients. Enzymes can also be added to help break down the seaweed.

To get useful nutrients from raw seaweed, its tough cell walls need to be broken down. This can be done with physical methods like ultrasound extraction, boiling, or freezing and thawing. Biological fermentation methods are also used to break down the cells. Physical extraction methods are often faster but cost more. They can also lead to lower crop yields in tests.

Seaweed extract has properties that help keep trace metal ions available for plants. So, extra micronutrients are often added to the liquid to give specific crops more fertilization benefits.

Organic fertilization methods have fewer environmental problems compared to making artificial chemical fertilizers. They don't use harsh chemicals to produce fertilizer. Also, seaweed is a renewable resource, unlike the minerals and fossil fuels needed for chemical fertilizers.

Large-scale use of synthetic fertilizer can make soil less fertile and increase water hardness over time. So, recent trends in farming are moving towards organic methods. This helps keep food production going by improving soil management and using natural fertilizers. Seaweed extracts are natural fertilizers that can also act as biostimulants. These are used to help plants use nutrients better and handle tough conditions.

New extraction technologies are being developed to make the process more efficient. They also aim to get specific compounds for special uses of seaweed biostimulants. However, specific extraction techniques are often kept secret by companies. Many liquid fertilizer extraction processes can also work well with other industrial uses for seaweed, like carrageenan production. This increases the economic benefit of the same seaweed crop.

How Seaweed Helps Nature's Cycles

To support the growing seaweed farming industry, many studies have looked at how different seaweed species affect nutrient cycles. They also explore how seaweed can be used for things like cleaning up pollution (bioremediation) and storing carbon.

Seaweeds can form very productive communities in coastal areas. They play a big role in how nutrients move through these ecosystems. As primary producers, seaweeds use inorganic carbon, light, and nutrients (like nitrogen and phosphorus). They turn these into their own body mass through photosynthesis. Harvesting seaweed from the ocean removes these elements, as well as heavy metals and pollutants, from the ecosystem.

For photosynthesis, seaweeds use both inorganic nitrogen, like nitrate (NO₃⁻) and ammonium (NH₄⁺), and organic nitrogen like urea. Using nitrate for growth is often called "new production." This is because nitrate comes from outside the ecosystem, like from upwelling (water rising from deep) or rivers. It has often been changed from other forms of nitrogen released by living things. However, using ammonium for growth is called "recycled production." This is because ammonium comes from inside the ecosystem, from things like fish and invertebrates. For example, ammonium released by fish in coastal areas can help seaweed grow by providing nitrogen.

Phosphorus is supplied as phosphate (PO₄^3-) and usually follows similar seasonal patterns to nitrate. Seaweeds also need inorganic carbon. This usually comes from the environment as carbon dioxide (CO₂) or bicarbonate (HCO₃⁻).

Like other ocean organisms that photosynthesize, such as phytoplankton, seaweeds can also have limited growth due to a lack of nutrients. Nitrogen is the most common nutrient that limits seaweed photosynthesis. But phosphorus can also be a limiting factor. The right balance of inorganic carbon, nitrogen, and phosphorus is also important for healthy growth. Generally, the N:P ratio for seaweeds is 30:1. However, this ratio can be very different among species. It needs testing to find the specific ratio for each type of seaweed. Understanding the link between nutrient cycling and seaweed growth is key to making seaweed farming better. It also helps us understand the benefits of seaweed uses, like fertilizer, pollution cleanup, and its role in the blue economy.

Too Many Nutrients in Coastal Areas

As the human population grows and industries and farming become more intense, more wastewater is released into coastal ocean ecosystems. This water often has high levels of nitrogen, phosphorus, and heavy metals. This leads to eutrophication in many coastal ecosystems. Eutrophication happens when there are too many nutrients in these ecosystems. This comes from pollution entering the oceans from industries, animal farms, and synthetic fertilizers. It essentially "over-fertilizes" these natural systems.

Eutrophication leads to a lot of growth in coastal systems. This can cause low oxygen levels (called hypoxia) and ocean acidification. These are two big worries for coastal ecosystems. A notable benefit of seaweed farming is its ability to clean up pollution. It does this by taking up too many nutrients in coastal ecosystems and then being used on land. Brown algae, partly because of their large size, are known for growing a lot and taking up many nutrients in coastal ecosystems. Studies have also focused on how to grow brown algae in the best way to increase their biomass. This would increase the amount of nutrients removed from these ecosystems. Studies have also looked into the potential of brown algae to store large amounts of carbon (called blue carbon).

Cleaning Up Polluted Ecosystems

Seaweeds have received a lot of attention for their ability to reduce eutrophication in coastal ecosystems. They do this by taking up nutrients during photosynthesis in integrated multi-trophic aquaculture (IMTA). Bioremediation means using living organisms to lower the amounts of nitrogen, phosphorus, and heavy metals in ocean ecosystems.

How well seaweeds can clean up pollution depends partly on how fast they grow. Their growth is controlled by many things. These include water movement, light, desiccation (drying out), temperature, salinity, and their life stage or age. It has also been suggested that in eutrophic ecosystems, phosphorus can limit seaweed growth. This is because the wastewater entering these ecosystems often has a high N:P ratio.

Bioremediation methods have been widely used because they are cost-effective. They reduce too many nutrients in coastal ecosystems. This leads to fewer harmful algal blooms and more oxygen in the water. Seaweeds have also been studied for their potential to absorb and collect heavy metals in polluted waters. However, the build-up of heavy metals might affect how well the algae grow.

Blue Carbon and Seaweed

Blue carbon methods involve using ocean ecosystems to store and bury carbon. Seaweed farming shows promise as a way to remove CO₂ from the atmosphere. It does this by taking up carbon during photosynthesis, turning inorganic carbon into its body mass, and then storing this carbon. This carbon can later be moved and buried.

Duarte et al. (2017) suggested a possible plan for a seaweed farming blue carbon project. However, there has been some debate about whether seaweed can truly remove carbon from the atmosphere. Krause-Jensen et al. (2018) say that for seaweed farming to be considered a blue carbon project, it must be very large in size and carbon storage rate. Also, humans must be able to manage the storage rate. Seaweed farming, including using seaweed as fertilizer, could become an important part of plans to fight climate change. It does this through carbon storage.

Benefits of Seaweed Fertilizer

The positive impacts conferred by seaweed fertilizer on crops.

Helping Plants Grow (Fertilization)

Seaweed works as a natural bio-fertilizer. It is rich in small and large nutrients, humic acids, and plant hormones (called phytohormones). This helps make the soil more fertile. Also, seaweed fertilizers contain polysaccharides, proteins, and fatty acids. These improve how well soil holds moisture and nutrients, leading to better crop growth. Seaweed has more trace minerals than fertilizers made from animal byproducts.

Using seaweed fertilizers can also help plants handle tough conditions. These are called abiotic stressors. They usually stop crops from growing well or producing much. Examples include low moisture, high salt levels, and freezing temperatures. These benefits seem to come from changes seaweed causes in plants. These changes include better energy storage, stronger roots, and improved metabolism. This helps the plant survive bad conditions.

Studies on Kappaphycus alvarezzi extracts have shown big reductions in electrolyte leakage. They also led to more chlorophyll and carotenoid production, and higher water content in plants. Research has also shown that wheat plants treated with seaweed extracts built up important protective substances. These include proline, other amino acids, and total protein.

Spraying seaweed fertilizer extract on leaves has been shown to improve how soybeans, like Glycine max, take up nitrogen, phosphorus, potassium, and sulfur. Research has also shown that brown algae seaweed extracts can improve tomato plant growth, overall crop yield, and resistance to environmental stress. Other known benefits of using seaweed as a fertilizer include less transplant shock, larger leaf surface area, and increased sugar content in crops.

Improving Soil Quality (Soil Conditioning)

As a soil conditioner, seaweed fertilizer can make the soil better physically. For example, it can improve air flow and water retention. Clay soils that lack organic matter and porosity (small holes) benefit from the humic acid and soluble alginates found in seaweed. These compounds stick to metal particles. This causes the clay particles to clump together, which improves the soil's texture, air flow, and water retention. It does this by helping clay particles separate. When alginates break down, they also add organic matter to the soil, making it more fertile.

Brown seaweeds like Sargassum are especially known for their valuable soil conditioning properties. This seaweed contains soluble alginates and alginic acid. These help bacteria break down organic matter. This process improves soil quality by increasing the number of nitrogen-fixing bacteria. It also adds more conditioners to the soil through the waste products these bacteria produce.

Cleaning Up Polluted Soils

Seaweed acts as a bio-remediator by absorbing harmful pollutants. Special groups of atoms on the seaweed's surface, like ester, hydroxyl, carbonyl amino, sulfhydryl, and phosphate groups, help absorb heavy metal ions. Seaweeds like Gracilaria corticata varcartecala and Grateloupia lithophila are good at removing many heavy metals. These include chromium (III) and (IV), mercury (II), lead (II), and cadmium (II) from their environment. Also, Ulva spp. and Gelidium spp. have been shown to help break down DDT in polluted soils. They may also reduce how much of it plants can take up.

While seaweed has great potential to clean up polluted soils, more research is needed. We need to fully understand how this process works in farming. Heavy metals collected by seaweed fertilizer might transfer to crops in some cases. This could have important effects on public health.

Another way to clean up and improve poor soils is by using biochar. Seaweed can be turned into biochar and used to increase the organic matter and nutrient content of the soil. Different types of seaweed seem to produce unique nutrients and properties. For example, red seaweeds create biochar that is rich in potassium and sulfur and is more acidic than biochar from brown seaweeds. This is a new area of research, but current data shows that growing specific types of seaweeds might lead to biochars that can be made for different types of soil and crops.

Fighting Pests and Diseases

Adding seaweed to soil can make plants healthier and more resistant to diseases. Seaweeds contain many active molecules that can fight diseases and pests. These include steroids, terpenes, acetogenins, and amino acid-derived polymers. Using seaweed extracts reduces the presence of harmful pests like nematodes (tiny worms) and insects.

While seaweed seems to reduce the harm from nematode infestations, combining seaweed with carbofuran, a chemical nematocide, seems to be most effective. Also, several seaweed species appear to slow down the early growth of many harmful insects. These include Sargassum swartzii, Padina pavonica, and Caulerpa denticulata.