One of the biggest conundrums for modern agriculture has been how to reconcile the demands of annual cropping against the need to preserve soil quality.
It’s taken a few thousand years for humans to recognize that there’s a reason why you rarely see bare earth in the natural environment. Soils that are covered by growing plants are healthier and happier micro-environments than soils left exposed to the elements for much of the year.
Here in Canada, farmers typically grow a crop during our short summer season and their land lies barren for the remaining eight to nine months of the year.
That’s a big improvement from the 1960s, when it was still a common practice to leave some fields empty for an entire year under what was known as summerfallow — ostensibly to preserve moisture and get weeds under control using extensive tillage.
Farmers have since moved to continuous cropping and minimum- or no-till practices, which means even though the field isn’t growing anything — except for a few weeds or volunteer plants springing up from unharvested seed — the residue from the previous crop is left largely undisturbed.
This has helped reduce soil and nutrient losses due to erosion and has stemmed the loss of organic matter.
Another evolution is now underway. A growing number of farmers and researchers are discovering the benefits of cover crops.
These "crops" aren’t planted for producing annual grains to feed people. Rather, they are planted solely for feeding the microbiological communities living in the soil.
It turns out that living roots — as opposed to the dead ones left over from the harvested crop — do a much better job of supporting those communities. The more soil microbiologists learn about those ecosystems living below the surface, the more fascinated they become over the potential spinoffs from enriching that environment.
If you think about it, it should come as no surprise to anyone that soil microbes can do a better job supporting plant growth if they aren’t having the roof of their house routinely ripped off by tillage and if they aren’t left to starve for eight months of the year.
The list of benefits is growing: reduced soil erosion, increased soil organic matter, reduced nutrient losses, better soil fertility, lower pest populations, weed control, less compaction, improved soil structure and improved water-management capacity. These fields can even be used as emergency forage in a pinch.
Cover cropping is really gaining traction in the American Midwest as farmers and regulators attempt to control the effects of nutrient loss into waterways and the growing "dead zones" in the Gulf of Mexico and Chesapeake Bay.
These techniques could help with water-quality issues we face in Canada, too, such as the health of Lake Winnipeg.
Interestingly, the research so far isn’t showing that cover crops actually increase yields in following crops. However, if farmers can reduce their applications of fertilizer and herbicide, their costs and risks are lower.
So we’re starting to see more Canadian farmers go into their fields after harvest and plant a cover-crop mixture of species ranging from grasses to legumes to plants such as sunflower or radishes that have deep taproots.
Even if these plants do die off during the cold Prairie winter, farmers can double the months that those soils are populated by living roots.
There are still unknowns. Some research is suggesting that extensive use of cover crops could lead to warmer winters because the dark plants will absorb more of the sun’s heat than snow. In the context of climate change, is that good or bad?
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