Seaweed to Improve the Soil – a New Zealand Success Story

Innovative solution explored by the Sailors for Sustainability
Seaweed to Improve the Soil – a New Zealand Success Story
Publ. date 4 Jun 2021
When New Zealanders Jill Bradley and her partner Keith visited an organic farm that used seaweed to improve the soil, it changed their lives forever. They researched which seaweed had the best qualities, and started a business to supply farmers with natural biostimulants. Some twenty-five years later, Agrisea is a sizeable player in New Zealand’s agricultural sector. The Sailors for Sustainability, Floris and Ivar, speak to Tane and Clare Bradley, the company’s current directors, to learn more about their business model and their products’ environmental benefits.

New Zealand: Productive but not sustainable

In a small campervan we drive to AgriSea’s head office in Paeroa, a small town in rural New Zealand. On the way there we see countless pastures with sheep or cattle. We pass orchards full of kiwis, apples, and avocados, mainly as monocultures. As in many countries, farming in New Zealand has scaled up and intensified considerably in recent decades. The use of nitrogen fertilizers, for example, increased by more than 600% in 30 years. It has led to reduced oxygen levels in rivers and lakes, which threatens freshwater species such as eels, mussels, crayfish, and whitefish. These are important food sources, especially for the Maori, whose food security has come under pressure as a result.

We also learn that many farmers here use agricultural poisons, despite it being unhealthy for soil life, water, and ultimately also people. Add to that the fact that synthetic fertilizers and agricultural poisons have a long, polluting supply chain that is highly dependent on finite supplies of raw materials and fossil fuels and you can only conclude that the average New Zealand farm is not very sustainable. How does AgriSea fit into this landscape, we wonder?

From research to business

Directors Clare and Tane Bradley welcome us to the family business. Tane explains the company’s origins: “Many years ago my mother and her partner visited an organic farm. Its crops were remarkably healthy and yielded astonishing amounts. The secret of the farm’s success? Seaweed. They were intrigued, and started researching seaweed for agricultural use. After much experimentation with all kinds of seaweeds, New Zealand’s native brown seaweed turned out to produce the best results.”

The couple realised that they had found a natural product with a plethora of uses and saw an opportunity. “In 1996 they started a company in seaweed-based soil improvement products. Their first customers were kiwi fruit growers, but soon more sectors became convinced of the benefits of seaweed,” Tane continues. “We now supply more than half of the wine grape growers and more than 15 percent of the dairy farmers in New Zealand,” says Tane proudly. “That’s impressive,” Ivar comments. “Can you tell us what seaweed actually does?”

Healthy soil biology

Before answering our question, Clare outlines farming practices in New Zealand: “Since the 1950s, agriculture has increasingly focused on optimizing fertilizers to increase yields. Although the initial results were good, we are increasingly seeing the negative long-term effects of fertilizers and pesticides. Not only do we pollute waterways and, according to some, also the food, the agricultural land is also becoming less productive.” The solution, according to AgriSea, comes from the sea.

“The basis of a healthy crop is healthy soil,” Clare proceeds. “Healthy soil is a collaborative, living ecosystem with billions of invisible microbes that need the right balance of nutrients to do their job. These microbes create symbiotic relationships between plant roots, soil nutrients, soil structure, and water. Without these relationships, plants cannot absorb the nutrients in the soil sufficiently.”

And that is the crux of the matter, Clare explains. “Without access to nutrients, plants are susceptible to pests and less resistant to drought. In response, farmers typically use more synthetic fertilizer and pesticide, which does not improve the soil. Our approach is different, as we focus on healthy soil biology. The bio-stimulants that AgriSea makes from seaweed are a food source for the micro-organisms in the soil. By feeding them, they can do their job and improve the soil. As a result, farmers who use our products can drastically reduce their fertilizer and pesticide use, grow more and healthier plants, and improve their environmental performance.”

Superfood for microbes

To show us how they make bio-stimulants from seaweed, Tane and Clare take us on a tour of the factory. In the warehouse area, large bags of dried seaweed sit on storage racks. Dried seaweed is ground into small pieces, then put in barrels and a water and a spice mix is added. The substance is stirred daily and ferments slowly. Ultimately, the pieces of seaweed are filtered out and a concentrated extract remains.

The remaining ‘tea’ is a superfood for soil microbes. It is full of minerals, vitamins, growth promoters, trace elements and amino acids that feed the soil biology. The remains of the ground seaweed are is suitable for animal feed, Clare explains. "So there is no waste in our production process!"

Renewable harvest

"Where do you source the seaweed?" Floris asks. "It would be a shame if more sustainable agriculture came at the expense of underwater ecosystems." “I totally agree,” Clare replies. “That's why we only use seaweed that is washed up on New Zealand’s beaches. We buy it from coastal communities and pay them a fair price of five NZ dollars per kilo. That means we receive sufficient supply and we support people who often have no other source of income. And importantly: they always leave some seaweed for the bugs on the beach.”

Less is more

We have another question for Clare and Tane: "For which type of farmer is AgriSea most useful?" "For basically all farmers," Clare replies. “Whether a farmer has pastureland with livestock, or grows fruit or vegetables, soil biology is very important for plant growth everywhere. Our seaweed mixes work in small quantities. When a farmer starts using our products, he can reduce synthetic fertilizer use by 25% in the first year. In year two he can reduce them by another 25% and in year three another 25%. It means that farmers can immediately save a lot of money. Furthermore, the plants can fight diseases better and the improved soil biology keeps the livestock healthier and yields better quality fruit.” It makes for an interesting business case with a short payback period, and environmental benefits to boot.


AgriSea’s story sounds very promising. Yet something troubles us. Over the past five years, we have visited several truly sustainable farms all over the world. From food forests, coffee plantations using natural fertilisers to permaculture farms; none of them required external nutrients to be highly productive. We have also learned that meat and dairy have an enormous ecological footprint due to land and water use and methane emissions. Does AgriSea contribute to sustaining a fundamentally unsustainable industry?

Clare speaks frankly: “The first customers of our bio-stimulants were organic farmers. When we tried to sell our products to conventional farmers we ran into some kind of wall. By inviting them and explaining how our products work, we convinced many of their economic and environmental benefits. As a result, we have helped many farms to become more sustainable. That has saved heaps of synthetic fertilizers and pesticides. We still have a long way to go, but by sharing our knowledge, more and more farmers are seeing the benefits and are switching. ”

We have learned during our travels that there is no silver bullet to make our food system more sustainable. The challenges are complex, and so are the solutions. For example, we think that more awareness, stricter laws and regulations, a better position for farmers, a switch to more plant-based and local food and agricultural methods that work together with nature are necessary to turn the tide.

After our visit to AgriSea, our seaweed scepticism has disappeared. Seaweed-based bio-stimulants are widely applicable and make a good business case. As far as we are concerned, it is certainly an important piece of the big puzzle to make our food supply sustainable.

Interested in more information on circular economy solutions?

In case you are interested in creating your own circular economy solutions, download our circular economy sprint paper to find out how, or send a mail to Johana Schlotter at to find out more.

Sailors for Sustainability is formed by Dutch sailors Ivar Smits and Floris van Hees who chronicle their sailing trip around the world in search of sustainable solutions and examples of circular economy thinking. The goal is to inspire their followers with positive cases while raising awareness of the urgency of sustainable change. Using renewable energy sources such as wind and solar energy, they travel sustainably. Finch & Beak is involved as a partner of the project to share the insights gained by Sailors for Sustainability to inspire sustainable business transformation.

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