Seaweed on land farms: who pays for it?

Seaweed has been used on land farms for centuries, as feed and as fertiliser. Today it is one of the markets the kelp industry is counting on. GreenWave's 2026 report on the industry in the United States and Canada names agriculture as one of three markets taking a growing share of kelp sold under contract. This note looks at what seaweed does on a land farm, what it costs, and who might pay for it.

Seaweed in cattle feed

A study by Borzouie and colleagues at Dalhousie University and Agriculture and Agri-Food Canada, published in Frontiers in Animal Science in September 2026, fed pregnant beef heifers a seaweed meal made from storm-tossed kelp and rockweed, bought from a supplier in Prince Edward Island. The trial was run at the Nappan research farm in Nova Scotia. The heifers received the meal at 0, 0.5, 1 and 2 percent of their feed for 50 days. Methane was then measured in chambers over two 24 hour periods per animal.

At 1 percent, methane fell by about 8.2 percent compared with the heifers that received no seaweed; at 2 percent, by about 8.7 percent. At 0.5 percent there was no clear effect. Growth, feed intake and weight gain were not affected at any level. The authors note the limits of their work: the methane measurements covered three to four animals per group, and they did not measure what happened inside the rumen.

What it costs, and what each tonne avoided costs

The study does not give a cost. We worked one out from published figures. At 1 percent of their feed, the heifers ate about 106 grams of seaweed meal a day. A PEI farm supplier's price list from February 2024 gives 54.22 dollars for a 25 kg bag of the same brand of meal, or about 2.17 dollars a kilogram. That puts the cost at about 23 cents per heifer per day, or about 84 dollars a year.

On the study's numbers, the 1 percent group produced about 0.96 grams less methane an hour, or about 8.4 kg less a year per animal. Using the standard factor that counts one kilogram of methane from livestock as 27 kilograms of carbon dioxide over 100 years, that is about 0.23 tonnes of carbon dioxide equivalent a year. Dividing the cost by the reduction gives about 370 dollars per tonne avoided. At 2 percent, the cost roughly doubles while the reduction barely changes, which puts it at about 640 dollars a tonne.

For comparison, Canada's industrial carbon price for 2026 is 95 dollars a tonne.

These are our calculations, and they rest on a small study, a reseller's price from 2024, and the assumption that the effect holds all year. They should be read as an order of magnitude, not a precise figure.

Seaweed as fertiliser

Seaweed fertilisers and biostimulants (products that help crops grow and cope with stress) are an older market than feed. Most of their raw material is wild seaweed. In Maine, the wild seaweed harvest, mostly rockweed, was worth 1.8 million dollars in 2024, or about 10 cents a pound. Farmed kelp in Maine averaged 53 cents a pound in 2025.

For a kelp farmer, this is the hard part of selling into agriculture: a buyer can choose wild seaweed at about a fifth of the price. At the same time, GreenWave notes that many wild sources have reached or passed the limit of what can be harvested sustainably, and that growth in this market will depend on farmed kelp. The report also says buyers increasingly want kelp processed into a set format and state (for example dried and powdered, or fermented) rather than fresh.

A small market with room to grow

According to GreenWave, about 0.5 percent of farms worldwide use seaweed biostimulants today, and estimates cited in the report put the seaweed biostimulant industry at 1.8 billion dollars by 2030. Six processing facilities in the United States and Canada now make kelp biostimulants, at least 20 companies buy from North American kelp farms, and another 20 report interest. In Canada, a Newfoundland company produced biostimulants from farmed kelp at commercial scale in 2025, and a BC company sold about 100,000 litres the same year.

What I take from this

First, seaweed does work on the farm. The feed study found a real, if modest, cut in methane without harming growth.

Second, at today's prices it is an expensive way to cut emissions. On our calculation, each tonne avoided costs several times Canada's carbon price. Someone has to pay that difference: the rancher, a buyer paying more for lower carbon beef, a carbon market, or government.

Third, for kelp farmers, agriculture is a market of volume and price per tonne. Farmed kelp will not beat wild rockweed on price. Its case rests on steady supply, known quality, and the limits of the wild harvest.

Discussion question

If you farm, ranch or make farm products: what would seaweed have to cost, or prove, before you used it?