Seaweed in Agriculture: A Natural Solution for Soil and Livestock

For centuries, coastal farming communities have harnessed the power of seaweed to improve soil fertility and supplement livestock feed. Today, modern research is beginning to validate these traditional practices, highlighting seaweed’s potential as a sustainable, nutrient-rich resource for agriculture. From improving soil health and boosting crop yields to enhancing livestock nutrition and reducing methane emissions, seaweed presents exciting opportunities for farmers. However, challenges remain in scaling up production and optimising its application.

This blog explores the role of seaweed in agriculture, its benefits, and the practical considerations for farmers looking to integrate it into their operations.

What is Seaweed?

Seaweeds are macroalgae—non-vascular organisms that absorb nutrients directly through their cell walls, unlike traditional plants that rely on roots and vascular systems. They thrive in marine and freshwater environments and play essential roles in aquatic ecosystems.

There are three primary groups of seaweed, classified by their pigmentation and physiological traits:

• Green seaweed (Chlorophyta)
• Red seaweed (Rhodophyta)
• Brown seaweed (Phaeophyta)

Seaweed has a long history of use in human and animal nutrition, medicine, and industrial applications. Today, it is increasingly being recognised for its agricultural benefits, including:

• Organic fertiliser and soil conditioner
• Natural plant biostimulant
• Supplementary livestock feed
• Soil pH amendment
• Carbon sequestration and climate mitigation

The Agricultural Benefits of Seaweed

1. Seaweed as a Soil Supplement and Fertiliser

Seaweed has been used as a natural soil enhancer for centuries. Modern studies suggest that seaweed-based fertilisers can improve soil health, enhance plant growth, and increase resistance to pests and diseases.

Nutrient Content and Biostimulant Properties

• Seaweed is naturally rich in potassium (K) but lower in nitrogen (N) and phosphorus (P), making it an excellent supplement to traditional fertilisers.

• It contains plant hormones such as auxins, cytokinins, gibberellins, abscisic acid, and ethylene, which promote:
  - Root development
  - Germination
  - Plant resilience to stress
  - Improved nutrient uptake

• The presence of alginate compounds allows seaweed to bioaccumulate heavy metals, potentially aiding in soil detoxification.

Application Methods

Farmers can apply seaweed to soil in several ways:

• Whole or chopped seaweed
• Powdered seaweed
• Aqueous extracts
• Seaweed composts

Observed Benefits in Crops

Studies have found that incorporating seaweed into soil management strategies can:

• Improve flower weight by up to 40%
• Reduce fertilizer requirements by 19%
• Increase germination rates and plant height
• Enhance antioxidant activity and disease resistance

2. Seaweed and Soil Health

Green macroalgae species, in particular, show promise for improving soil health. Research suggests that:

• They can help suppress harmful fungi and pathogens, reducing the incidence of plant diseases.
• Their application may protect crops against soil nematodes, offering a natural alternative to chemical nematicides.
• Their alkaline pH can serve as a natural liming agent, helping to balance soil acidity.

A study on sugarcane growth found that using seaweed-based compost resulted in four times higher biomass production than standard compost.

3. Seaweed in Livestock Feed

In addition to improving soil health, seaweed has significant potential as a supplementary feed for livestock. With high protein levels (up to 47%) and beneficial omega fatty acids, seaweed can serve as an alternative protein source, particularly for ruminant animals.

Environmental Benefits: Reducing Methane Emissions

One of the most exciting findings in seaweed research is its potential to reduce methane emissions from livestock. Certain red seaweed species contain bromoform, which inhibits the final step in methane production in the rumen.

• Studies have reported methane reductions of up to 100% in short-term trials and 98% over 90 days.
• Other research has shown mixed results, highlighting the need for further large-scale studies.

Challenges in Livestock Use

Despite these promising findings, barriers to large-scale adoption include:

• Palatability issues: Some livestock may find seaweed unappealing, affecting feed intake.
• Optimal inclusion rates: While sheep trials have successfully included up to 12.8% seaweed in diets, other studies have found lower tolerance levels.
• Processing considerations: Extracting active compounds from seaweed could enhance effectiveness while minimizing negative effects.

Challenges and Barriers to Widespread Adoption

Despite its potential, integrating seaweed into mainstream agriculture faces several challenges:

1. Supply Chain and Scalability

• Seaweed production needs to be scaled up to meet agricultural demand sustainably.
• In the UK, most seaweed is imported from Asia, raising concerns about cost, quality, and sustainability.
• Increased investment in local seaweed farming could reduce dependence on imports and enhance availability.

2. Storage and Decomposition Issues

• Fresh seaweed ferments quickly, which can lead to nutrient loss and unpleasant odours.
• Proper composting and stabilisation methods are needed to preserve its beneficial properties.

3. Regulatory Considerations

• More research is required to establish best practices for application rates in different soil types and farming systems.
• Livestock feed regulations must ensure safe inclusion levels of seaweed without adverse effects.

Future Prospects for Seaweed in Agriculture

The global interest in seaweed farming is growing, with seaweed now accounting for 30% of total marine aquaculture production. If cultivated sustainably, seaweed could play a key role in the future of regenerative agriculture by:

• Providing a renewable, low-carbon soil amendment
• Reducing the need for synthetic fertilisers
• Enhancing livestock nutrition while lowering methane emissions
• Supporting sustainable farming practices such as cover cropping and agroforestry

Conclusion

Seaweed is a versatile and promising resource for agriculture. While challenges remain in supply, application methods, and livestock adoption, ongoing research is unlocking new ways to integrate it into sustainable farming systems. Green seaweeds offer significant potential for soil enhancement, while red seaweeds hold promise in reducing methane emissions from livestock.

As farmers continue to seek natural and effective solutions to improve soil health and livestock productivity, seaweed may soon become an indispensable tool in regenerative agriculture.

Are You Ready to Try Seaweed on Your Farm?

If you’re interested in incorporating seaweed into your farming practices, consider starting small:

• Experiment with seaweed composts or liquid extracts to assess soil response.
• Look for locally sourced seaweed to minimize costs and environmental impact.
• Stay updated on emerging research and best practices.

By embracing this natural resource, farmers can contribute to a more sustainable and resilient agricultural future.