Tom Forge
Tom Forge taking a soil core from a cover crop plot.
Long hailed for their ability to enhance soil health and improve stability, cover crops have often been seen as something specifically for the vegetable-growing set of farmers. But it turns out, that grass alleyway between the rows of perennial plantings has more to offer than just a pretty visage.
While studies are ongoing as to how to make cover crops work harder and better in perennials, some of the benefits seen in annuals do translate to orchard, vineyard and berry fields. Interest in this technique is on the rise.
Tom Forge, applied soil ecology and nematology scientist with Agriculture and Agri-Food Canada, says there are five significant benefits of cover crops in perennials: Reducing soil erosion (limiting dust and mud), reducing nitrate leaching, moderating temperatures, weed control, and increasing organic matter for enhanced soil biological activity.
DeLisa Lewis is the co-owner and lead farmer of Green Fire Farm in Duncan and has established perennial forage and clovers within perennial crops. She also happens to be the assistant professor with the Faculty of Land and Food Systems with The University of British Columbia, so has had “a fairly strong focus” in cover cropping, though her research is centered in annuals when not trying out the application in perennials on her farm.
“The benefits with reduced/eliminated tillage in those perennial alleys are reduced/eliminated risk of erosion,” she says of the perennial cover crops.
Ensuring soil stays in place is essential for a wide range of reasons, but cover crops can be particularly important for those on the ‘wet coast' because they reduce compaction of the soil.
“In the wet Lower Mainland and Vancouver Island, this translates to improved drainage which can be critically important for getting into fields early in the spring,” says Forge.
Cover crops can also add to the beautification of an area, although what may be seen as aesthetic to some, may be seen as food to a pollinator. Lewis hasn’t yet measured the increase in pollinators due to her cover crops.
This linkage between pollinators and cover crops is something Forge identified as a benefit.
“Different types of cover crops are often examined for their attractiveness to pollinators and natural enemies of insect pests,” he says.
Cover crops, borders and hedgerows may be considered adornment at consumer-facing farms, but lavender interspersed in a vineyard, fescue grasses between u-pick raspberries, or clover in the alleys of a cidery’s apple orchard, while pretty, are also helpful at all perennial-growing sites.
“Soils benefit from keeping a cover, keeping a living root in the ground, it is a basic principle of soil health,” Lewis says.
In cases like Lewis’, the cost of maintaining a perennial cover crop is lower compared to an annual cover crop due to reduced costs for seeding and maintenance. Jason Smith (whose farm is profiled on page 53) also uses perennial cover crops in his blueberries.
“I have a permanent cover crop mix of rye and fescue in the middle of rows,” he says. “I used to do the annual thing. The grass part was cheap, but all the labour to prep for seeding, seed, roll, etcetera, was too expensive with the returns we are getting now.”
Smith focuses on the alley section between berry crop rows and reseeds when seepage and rain damage the field and lead to rutting.
While there is less planting with perennial cover crops, it’s a more complex system says Eric Brennan, research horticulturalist with the USDA Agricultural Research Service.
“It depends on the type of system,” he explains. “The needs for a grape crop are quite different from, say, an orchard system.”
A similarity between annuals and perennials he mentions is that farmers don’t want cover crops to compete with the main crop.
“Most of the benefits of cover crops relate more to their effects on the overall agro-ecosystem than on fruit production, per se,” says Forge.
The overall best choice is turf-type mixtures of perennial grasses which are often marketed as Alleyway Mix and include fescues and/or rye grasses.
“With perennials, growers are limited to planting the cover crops in the alleyways between the crop rows and herbicides are usually used to keep the crop row relatively weed-free,” he says. “This limits the potential to increase organic matter and beneficial biological activity in the crop row.”
He says that it is possible to “mow and blow” clippings to enhance organic matter, but the traditional flail mower needs a side-discharge mechanism to get the clippings into the crop row.
“The planting of cover crops within the crop row, also known as ‘living mulch’, has been the holy grail of cover crop research,” he says. “The idea is to identify a cover crop that can provide the desired benefits directly to the soil in which the target crop is growing, but without competing with the target crop for water or nutrients.”
So far, a cover crop that fits this bill hasn’t been identified.
“Many vineyards in the US and a few in BC experiment with tilling every other alleyway, or perhaps every third alleyway, each year,” he says. “This is an attempt to get a compromise between the benefits of the perennial cover crops while releasing nutrients back into the soil.”
Those considering cover crops for perennial crops need to assess a variety of factors such as soil test data, rain fall and irrigation, production system requirements, pest and disease pressures and crop nutrient needs. Cover crops do benefit perennial plantings so long as costs and benefits are considered prior to planting and a certain amount of the unknown is accepted. ■