There’s a revolution growing below us. A group of passionate farmers have been experimenting with complex combinations of cover crop seed species which may significantly influence the future of sustainable farming. Have plant biologists kept up with these pioneers? Could species be bred to provide better cover crop soil results?
Pioneers in the last decade have shown how cover crops are not just necessary to prevent soil loss, but also to develop biota, rejuvenate biodiversity, “sweeten” the soil and literally grow the earth. Weeds, pests and disease can be managed with the correct cover varieties. Together with no-till farming, this revolution has become known as “conservation agriculture.”
By developing the soil, farmers are protecting their land from erosion. Water tables are protected as runoff is reduced, the soil becomes richer and more porous. As soils are fed a wide variety of nutrients, organic matter increases, nitrogen levels improve, and farmers can fertilize less. With less tillage, more CO2 is sequestered in the soil and less diesel emission is released.
What Seeds are Best for Cover?
While some farmers would say “the more seed variety, the merrier”, others want to have deep rooting plants, fibrous roots and those that can survive into colder weather. Time and cost are important. If farmers are planting covers in August, a larger investment may be justified. A faster growing plant with a quick uptake is important if farmers can’t manage to seed until well into the autumn. Strategy also varies if cover is combined with manure.
As farmers get better at combining cover crop species, some, like Jake Freestone, vary seed varieties according to the next crop in rotation. Jake was involved with the NIAB and Kellogg’s Origins project assessing cover crop trials. They produced a ‘cookbook’ style menu cataloging the strengths and weaknesses of the cover species entitled: Cover Crops: A practical guide to soil and system improvement, 2016/17.
Slugs. In cooler climates, cover crops can create a green bridge allowing slugs to proliferate (creating the costly necessity to apply slug pellets). Several farmers want breeders to focus on creating cover plants that are less tasty for slugs.
A contrary concern has been planting cover in drought conditions (not only for failure to uptake, but also the risk of further exacerbating water tables should plant cover be insufficient).
What is the perfect cover seed?
Farmers are more concerned about stronger roots than tops, letting in more light and less flower. A fibrous root helps open the soil, increase organic matter and promote biota. It’s about creating a “below-ground biomass”. Certain crops work as vaccines to prepare the soil to better resist diseases. Outside of the slug issue, cover crops should repel pests that may threaten harvests.
Termination is an important topic. As Tom Jewers said: “We don’t want cover crops to become a weed, so ideally, they need to grow rapidly, but never set any seed!”
Some Contrary Views
Every soil, every climate, every crop is different. Not every farmer uses cover crops in the same way – this practice is anything but a one-size-fits-all. Some are blessed with ideal conditions without the need to actively intervene; some have mixed farms with ample manure; others with early winters or wet conditions would not benefit very much. A lot more research needs to be done.
Several farmers raised the issue of the cost of seeds, noting how natural off-season growth (volunteer re-growth) can be sufficient to regenerate soil. Seed merchants often offer complex blends many farmers find unnecessary (some are blending their own). Farmers also need to acquire extra machinery to allow planting through dense cover without disturbing the soil. Then there is the demand on time (usually just after combining) and diesel fuel.
While farmers agree cover crops are beneficial, there is much debate on the “what” and the “how”.
Glyphosate is Vital
Complex cover cropping has been made possible with inexpensive glyphosate-based herbicides, allowing an effective termination process. Many farmers standing up for the environmental benefits of conservation agriculture could not imagine the losses to biodiversity should the activists succeed in banning the herbicide.
The threat to glyphosate is the biggest challenge for cover cropping. The organic lobby rejects conservation agriculture as farming with a chemical plow. Since organic farmers are not allowed to use synthetic herbicides, there will likely be more pressure to fully ban glyphosate in the EU.
And that is more pressure on the soil, farmers and consumers.