In the Brandt Family Farm office, there is a collection of 15 soil cores taken from various fields across the farm with different soil types.

Most were taken in 2009, but there are three comparison cores taken in 2022 that help visualise the remarkable changes that multispecies cover crops have made to the soils on the Brandts’ 400ha farm in Carroll, Ohio.

When David Brandt first came to the farm in 1971, soil organic matter levels were just 0.75%, but under his management they reached 8% – an improvement visible in the darker soils in the newer soil cores.

See also: How US farmer increases profitability through relay cropping

He started practising no-till in 1971 and introduced single-species cereal rye cover crops in 1976 when he noticed yields decreasing.

Godfather of soil health

His success in making both practices work on the farm is just one of the many reasons David Brandt became known as the “Godfather of soil health” in US regenerative agricultural circles, and why growers from across the US and around the world have flocked to his farm and his field days.

He even became the subject of a popular social media meme after saying about his career: “It ain’t much, but it’s honest work.”

Sadly, David passed away as the result of a motor vehicle accident last May, leaving his grandson Chris to take over management of the farm.

Cropping

Chris has been full-time on the farm since 2017. In common with most farms in the Midwest states, he grows corn (maize) and soya beans.

A little less common, the farm has 20% of its area under winter wheat, which has become a key crop on the farm, helping provide the time for a multispecies overwintered cover crop to develop ahead of the following season’s corn.

“A lot of farmers double-crop soya beans by planting them into wheat stubble,” Chris explains.

“We do a bit of that, which gives an immediate monetary return, but we also want to get the later return from planting a cover crop ahead of the corn.”

With wheat harvest in early July, multispecies cover crops have plenty of time to grow, leading to the high-biomass covers that regenerative farmers in the US have become famous for.

“These are the crops that make the difference to organic matters,” Chris says.

While David had been using cover crops since 1976, it wasn’t until he met cover crop advocate Steve Groff and North Dakota farmer Gabe Brown in the early 2000s that he started experimenting with cover crop mixes of six to 10 species.

Soil health

“Fields that are now 8% organic matter were only sitting at 3-4% back then,” Chris says. “If you use monocrop covers, whether it’s buckwheat, rye or clover, you won’t see a strong increase in organic matter.”

Increasing organic matter provides a lot of benefits in the field, such as improved soil structure and water holding capacity, he says.

“For each percentage point of organic matter, you can hold significantly more water in the soil, and if it can hold water, it can also infiltrate.”

His soils can infiltrate 9in (22.8cm) of rain an hour, so it takes a very significant rain event to trigger surface erosion, and because of that, it also reduces nutrient loss.

“Between the improved soil structure and increased rain infiltration, we can get machinery on fields after rain significantly sooner than our neighbours,” he says.

Another benefit is increased biological activity. “We have more mycorrhizal fungi, which as a network help bring nutrients to plant roots, so plants are better able to utilise applied nutrients.

“Generally, in the US, it’s said one pound per acre of nitrogen in a corn field will lead to one bushel per acre of corn.

“What we see [on the Brandt farm] is that one sixth of a pound of nitrogen becomes one bushel of corn, so we’re more effective at getting those nutrients to the plant,” Chris says.

Grazed cover crops

Perhaps surprisingly, though, last winter was the first time the Brandts had experimented with grazed cover crops using 250 sheep owned by a neighbouring farmer.

“There’s not that many sheep in this region, and we don’t really want to put cows on a field going into corn the next year,” Chris explains.

“But the biggest problem is not having any fences, and it’s hard to justify putting them in.”

The sheep mob-grazed various sections of the field for two to three days from the end of November to early January, with Chris keen to see if the benefits from sheep grazing outweigh the potential disadvantages from losing biomass and possible compaction.

The core components of the farm’s typical cover crop mix before corn are cereal rye, hairy vetch and crimson clover.

These generate large amounts of biomass, suppressing weed growth and shading the soil from the sun, while the legumes also fix nitrogen to reduce fertiliser inputs.

Sunflowers, pearl millet and flax are added to mixes where the farm is looking to promote mycorrhizal fungi propagation on newly aquired land, to add feed value for grazing, or to increase micronutrient content in the topsoil, Chris explains.

“Sunflower roots will pull zinc up from areas where corn roots won’t normally reach,” he says.

But the sheep trials are pushing him to try more specialised mixes containing Sudan grass (a relative of millet), oats, forage radish and grasses that will provide better feed and nutrition for the sheep.

“What mix to use depends on what kind of practice you’re aiming for,” he says.

Cereal rye

Simpler cover crops are used ahead of soya beans, the other spring crop in the rotation, but play an equally important role.

These covers follow corn harvest in October or November, which means they are planted later than when following wheat, restricting selection of species to mostly cereal rye or other cereals.

Cereal rye has the advantage of a much larger root structure than wheat, and it seems to have either an allelopathic or competition effect on mare’s tail, a key weed of soya beans.

“It’s one of the hardest-to-control weeds in soya bean, so the fact cereal rye seems to almost completely displace it is a significant reason to use it,” Chris says.

Benefits from cereal rye are apparent from planting dates until Christmas, “but you don’t get much growth if you plant it past the third week of November, so it’s usually planted by then.”

Growing a cereal rye cover generally leads to an increase in soya bean yields of 3-5bu/acre (0.2-0.33t/ha), Chris says.

“Soya beans require 2-4 units of nitrogen for every bushel they produce, and usually it nodulates to generate two to three of those.

“So the more nitrogen you have in the ground, the lazier the soya beans are, and they won’t nodulate as much, which reduces yield.

“The theory is the rye takes away nitrogen from the soil and forces the soya beans to nodulate more, increasing the base yield.”

Another important role for the terminated rye is protecting the soil from the area’s high summer temperatures, which can reach 35C or more.

“It causes all biological activity in the soil to cease, including plant root growth,” Chris says.

Typically, the rye cover, like the multispecies version after wheat, is planted with a Kuhn (Krause) direct drill, although in some years when time is short Chris will spread cereal rye seed through a fertiliser spreader.

“You can do more acres per hour, but the stand can be thinner.”

The soya beans are then planted into the cover before termination, usually with a crimper-roller.

“We’ve found if you terminate early and get rain, which is common, the ground gets wet and, with the rye laid over, the wind cannot get in to dry the soil, and you get a wet, sloppy mess.”

Crimper-roller termination after drilling works well as long as the cereal rye has begun flowering, when breaking the stem will kill the plant, Chris says.

Rolling also helps ensure any open seed slots from the direct drill are closed, improving germination.