From late winter to early spring, cold waters in Long Island Sound create the perfect environment for long dark-brown and green lasagna-shaped seaweed strands to thrive. Attached to a rocky seabed or flowing from a stretch of rope suspended between buoys is sugar kelp, Saccharina Latissima. Its ribbon-like strands can grow as long as twenty feet or more providing habitat for juvenile fish and small invertebrates.
In addition to being used as a sweetener and thickening agent in commercial products and a popular ingredient in restaurants and home kitchens, sugar kelp can supplement traditional nitrogen-based fertilizers while providing water quality improvements.
“Long Island Sound is impacted by nutrient pollution, namely nitrogen pollution,” said Kimarie Yap, the Long Island Sound Study’s Bioextraction Coordinator. “This causes water quality issues, such as algal blooms, the depletion of oxygen in the water that marine animals need to breathe (known as hypoxia), and large-scale fish die-offs.”
As it grows, kelp absorbs excess nitrogen and other nutrients in the water column, acting as a filter and preventing algae from using the nitrogen, which can result in harmful blooms. Nutrients are absorbed into the seaweed’s tissue, making sugar kelp a natural source of micronutrients which are important for the yield, quality, and flavor of agricultural crops. Seaweed aquaculture of farmed kelp can support bioextraction in the Sound—the process of growing and harvesting shellfish and seaweed species in order to remove extra nutrients from coastal waters. Previous work in the western and central Long Island Sound has estimated that sugar kelp can remove between 38–180 kg 1 of nitrogen per hectare in a growing season.
Part of the Long Island Sound Study (LISS) Bioextraction Initiative is a Sugar Kelp Fertilizer Pilot Study, which launched in the spring of 2020. Researchers and agriculture specialists are setting out to determine if sugar kelp can be grown, harvested, processed, and successfully used on Long Island to support water quality and agricultural growers.
“On Long Island, we have sandy soils,” said Sandra Menasha, Vegetable/Potato Specialist with Cornell Cooperative Extension of Suffolk County. “Because of that, our soil does not hold onto the micronutrients that a plant needs very well because sand is all negatively charged, and so are a lot of our nutrients. Sugar kelp is known to be full of a lot of micronutrients. So, it can kind of replenish the soil.”
“This is where bioextraction’s strength comes into play, said Yap in a recent article about the pilot published in the Long Island Nitrogen Action Plan newsletter. “It is a management strategy currently available that can remove existing nitrogen after it has entered Long Island’s embayments.”
First-phase trials using sugar kelp fertilizer amendment were conducted in greenhouses at the Long Island Horticulture Research and Extension Center in Riverhead, New York. Two trials were conducted on tomato seedlings and tomato and petunia plants.
“[Working in the extension center] allows us to do more closely watched, smaller plot replicated studies to get a sense about what treatments work, what doesn’t work,” said Nora Catlin, PhD, Agriculture Program Director and Floriculture Specialist and Menasha’s collaborator on the pilot. “Then we bring them on to the farm and try them out with a grower and do it on a bit of a larger scale. My interest was primarily in seeing if this sugar kelp, compared to other similar amendments on the market, could fit in that same space of how those are used.”
“If seaweed, such as sugar kelp, could be grown locally and used as fertilizer to impart the nutrients naturally taken up by the seaweed onto lawns and gardens, this could potentially help close that nutrient loop and would be a better, more sustainable option for both marine and agricultural industries compared to importing kelp fertilizer, and thus excess nutrients, from other states,” said Yap.
Sugar kelp in the first round of greenhouse trials was grown in Riverhead on the north shore of Long Island. Subsequent trials used kelp cultivated on mooring lines in the East River, located in the Bronx, New York. First rinsed thoroughly with fresh water and line dried, the kelp was then cut, crushed into small pieces, dried in an oven and ground into a course meal. In addition to the meal, an extract was made from boiling dried kelp with water. However, later iterations of the study have not included rinsing the seaweed as researchers found little affects in salt concentrations between rinsed and unrinsed samples.
“After hearing from other researchers, we tweaked that formula because we heard from other folks that they weren’t finding a lot of differences between their rinsed and unrinsed kelp,” Catlin said. “For the sake of time and thinking about if someone were to do this step as a grower, we took that into account.”
In June of 2020, field trials on tomato plants showed no significant difference between plants with or without the fertilizer amendment. In addition to observational data, soil samples were taken and evaluated for nutrient levels, pH, soil electrical conductivity (the ability of soil water to carry an electric current), and organic matter. Fruits were harvested and sent off for nutrient and sugar analysis, and data was collected on yield and quality.
“For field production, tomatoes are the king of most farms,” explained Menasha. “Most farmers are willing to spend more on amendments to increase production and quality of tomatoes, whereas something like radishes have a small profit margin…your benefits aren’t going to be as realized.”
Research thus far has shown some mixed but promising results. Fruit analysis testing showed higher sulfur levels in kelp amended plots compared to plots that did not receive any kelp amendments. Research from Rutger’s University finds that sulfur applications to some crops, including tomatoes, can enhance their quality and flavor.
“When we analyzed the tomato fruit from this trial, where we had sugar kelp, we had higher levels of sulfur in the fruit,” said Menasha. “So, I can infer based on the research from Rutgers that there is likely a better taste in that tomato. Taste and quality are what keeps people coming back, so that’s a huge impact.”
CCE’s specialists were not, however, able to measure many of the reported benefits that people believe kelp can offer. But comparable results were generated between the pilot’s fertilizer amendment and commercially available kelp fertilizers, a good sign that future fertilizer supplements could be produced from Long Island Sound grown kelp and used by local growers, bypassing the need to introduce kelp fertilizers (and thus nutrients) from outside the region.
Moving into the next phases of the study, Catlin plans to explore the utility of different amendment products.
“I definitely want farmer input to see what form they wanted to use,” said Catlin. “Do you want to use kelp extraction? Do you want kelp meal? The farmer I worked with felt the meal would work better for his production system. But broadly, you want to engage grower input.”
Caitlin and Menasha also plan to explore how tomato plants could react to double treatment: grown with the kelp fertilizer amendment in greenhouses and treated with the amendment at field planting.
This pilot is funded by the Long Island Sound Study. $54,643 was awarded to Cornell Cooperative Extension for the most recent phase of trials.
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