Giving the soil a bit of breathing room
By Luke Edwards
When the growing cycle for a crop ends, greenhouse operators want a clean split, not a messy breakup.
Getting the greenhouse cleared out so they can bring in a new crop simply means the next payday comes a little sooner. It’s simple economics.
And it’s what makes the extra effort St. Davids Hydroponics unique. While many other greenhouses choose the quickest and most efficient option - clearing everything out and trucking it to the nearest landfill - staff at St. Davids spend hours taking the plants down without the strings and clips that make recycling a headache. It takes time and money, but it allows them to turn the spent plant material into a soil amendment that a local grape grower happily takes.
“Most greenhouses aren’t doing what Maarty and St. Davids is doing,” said Grodan’s Yianni Monahan, at an event held last month at Vineland Research and Innovation Centre.
However, having that local grape grower connection is key. Chief grower Maarty Hendriksen said they don’t mind taking a few extra steps when they still know they can get the product out the door relatively quickly.
“We’re just looking at how to get it away from our greenhouse as easily as possible.”
VRIC and Grodan have been working together on a project that focuses not on the plant itself, but the substrate in which it grows. And the event last month offered some early insights into trials held this summer to see how using spent stone wool could act as a soil amendment for crops, much like the vine and above ground material that ends up in vineyards.
Research scientist Jason Henry said it’s a matter of “shifting waste to a resource.”
“We need to show there are demonstrated benefits,” he said.
Henry and his team have been researching the possibility for several years, though said the existing literature on reuse of spent stone wool is sparse. Thanks in part to a grant from the Greenbelt Foundation, researchers at Vineland this year were able to run tests in the TreeCulture park where they grew corn and broccoli and used a variety of soil compositions that included various mixtures of soil, fertilizer and the spent stone wool soil amendment they’ve developed.
What stone wool offers, Henry said, is a little breathing room in the soil.
“This is where the air and water can enter in,” he said. “This is what makes substrate very powerful.”
By offering that space, the stone wool amendment can help the hydrogeological process, making the water and nutrients in the soil more available to the plants.
“There’s a tug-of-water battle that goes on,” he said, describing some soils as less of a water giver than growing media used in greenhouses.
Monahan described a few barriers to making the reuse of stone wool viable. First, growers and farmers need to be convinced it’s safe, simple, and accepted by regulators. It also needs to make economic sense.
“We want to make a pathway that makes sense to operators,” he said.
Vineland’s results with the sweet corn harvest did show some promise. Treatments that included stone wool and another that included both stone wool and hen manure had higher mean marketable cob weights compared to the untreated control.
Testing on soil characteristics had less conclusive results, partly thanks to the wild weather this summer.
Based on research, including simulations the team ran, Henry said the stone wool amendment could be a climate resilient amendment, especially during droughts. That’s a large reason why there’s been interest in the United Kingdom, where there’s been interest to reprint an article explaining his group’s findings.
Monitoring for the broccoli trial was ongoing this fall, with harvest expected to take place in November.
Offering up the grant for the Vineland/Grodan project made plenty of sense for the Greenbelt Foundation, said Ryan Carlow, program lead with the foundation. He’s been involved with his own lengthy project researching soil characteristics for farmland in Niagara and the Greater Golden Horseshoe. Overall, he said improving soil resilience can only benefit growers into the future.
“Anything that can improve water storage capacity, they’re really interested in,” he said.
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