Cold, wet and waterlogged soils are just a fact of life in many fields across Manitoba early in the growing season, and growers have no choice but to wait out the moisture.
The biggest challenge is that it can be weeks before soils are dry enough to be able to walk fields, let alone drive in with equipment. That means the already short growing season gets shorter, and precious time that could be spent growing a profitable crop is lost.
Afua Mante, an assistant professor in the Department of Soil Science at the University of Manitoba, is exploring how cover crops, like fall rye, can be used to improve soil trafficability – the ability of soils to carry vehicular traffic and withstand the weight of machinery. This way, growers can get into their fields faster, without getting bogged down to the axles or causing serious compaction.
“Soil trafficability is a major issue under our climate at the beginning of the growing season – especially in the heavy, clay soils of the Red River Valley area,” explains Mante. “For farmers, it’s incredibly difficult and frustrating, as any day delay has ripple effects on plans.”
Creating and protecting root channels
The main idea behind Mante’s work is surrounding fall rye. Growers seed fall rye in the late summer for the following spring. The fall rye then puts on enough biomass so that it can take up moisture. At the same time, the rye’s root system forms natural channels that help with water movement down into the soil profile.
“It’s about achieving a good balance – you’re removing the excess moisture that prevents you from getting onto your fields, while still storing that moisture deep in the soil profile for drier periods,” says Mante.
She adds that, for the fall rye to be effective at regulating excess water, it needs enough of a chance to establish, so that it can actively remove water and create the root system channels.
Much comes down to the timing, and Mante and her fellow researchers are trying to nail down the ideal seeding date for fall rye, so that it has between four to six weeks to establish before the temperature drops to around 10 C.
“The conventional recommendation has been to seed fall rye on or around the week of September 15. But by the time you get to that date in Manitoba, we have less chance of having four to six weeks for good establishment before the temperature cools down,” says Mante. “Our field work is showing us that it’s too late to give fall rye a good head start, so you won’t see any major improvements in regulating moisture.”
Mante notes that, even if the fall rye isn’t quite developed enough to deal with surface water, growers are still helping to build up soil carbon and microbial communities.
Re-thinking cover crops for year-round soil protection and more
While Mante is focused on the impact of cover crops on early-season soil water regulation and trafficability, she says growers need to reimagine the way they use cover crops to protect their soils year-round.
The use of cover crops in Manitoba is a well-known and proven practice for preventing erosion during the off-season.
But in addition to erosion prevention, Mante says that cover crops – when seeded at harvest, or inter-seeded with canola, soybean or cereal crops – help to build and preserve root channels that move moisture away from the soil surface and into the soil profile. This helps reduce the risk of drought conditions during the season.
Specifically, having well-established cover crops can also reduce the potential damage from high-intensity rainfall that often follows dry periods.
“It’s the drought periods that we have to be more concerned about. Because around that time, it gets dry and goes on for a few days or weeks. Then, suddenly we’ll receive 40 millimeters of rainfall in the span of an hour,” explains Mante. “And the rate of deformation of the soil under such a condition is huge compared to if you took your time and allowed water to move through over two or three days.”
This soil deformation leads to surface crusting, which essentially seals off the soil to water and increases runoff.
“If that water isn’t percolating through deep soil layers to store water for drought conditions, then your soil is going to be at greater risk,” says Mante.
Adopting an integrated management and systems approach
Trafficability and soil structural protection are one aspect of a larger ongoing cover crop project at the University of Manitoba, with funding support from the Sustainable Canadian Agricultural Partnership program, Manitoba Crop Alliance, Manitoba Canola Growers, and Manitoba Pulse and Soybean Growers.
Mante is part of a team that includes Yvonne Lawley, Department of Plant Science and Francis Zvomuya, Department of Soil Science.
Together, the researchers are exploring ways cover crops can be integrated into farm management practices to support agronomic goals while also improving soil health for sustainable crop production and a healthy environment.
“When you think about these soils across the province, they have been in production for a long time,” says Mante. “While intensive agricultural practices have been instrumental in the progress we have made as an industry, we also recognize that these practices are associated with risks such as soil compaction, salinization and erosion. For that reason, we need to adopt beneficial management practices that reduce these risks and ensure our soils can support crop production and other ecosystem services.”
Continued research is essential. As much as cover crops have the potential to bring major benefits, timing is still a challenge since they need to be seeded after harvest – and that can be difficult following certain crops in Manitoba.
Mante also cautions that the positive effects of cover cropping – like moisture regulation – aren’t going to be seen or felt instantly. “We need patience,” says Mante, “and a systems approach that takes the entire year, the climate, soil characteristics and agronomic practices into account to first allow the soil to heal.”