Double your organic matter

When Jason Birdsong took over his family’s farm near Prospect, Tennessee, a little more than 20 years ago, he saw degraded soils and stagnated corn and soybean yields. His father had already begun switching to no-till, but the younger Birdsong picked up the pace and completed the transition.

Crop yields improved, but soil health and compaction lagged. Searching for a way to improve the soil further, he started growing cover crops on half the farm, and the transformation to better soil health mushroomed. By 2010, he grew cover crops on the whole farm.

Today, the organic matter in his soils has doubled compared to the level two decades ago, making Birdsong—named a Soil Health Champion by the National Association of Conservation Districts—a devout cover crop grower regardless of economics.

“Because of all the benefits they provide, growing cover crops has just become part of our program,” he says. “We feel like if we started cutting them out, we’d lose so many of the benefits we’ve already gained.”

It starts at harvest

Birdsong drills a cover crop mix “right behind the combine” when harvesting either corn or soybeans. The amount of residue on the soil surface of fields just before harvest determines what cover crop species he plants. If residue is declining, he adds more carbon-rich species to the mix. If residue is rising, he adds more nitrogen-rich species.

“We look at the soil surface going into harvest,” he says. “Last fall, in 2022, just before we harvested corn in late August through September, we found that the surface residue had diminished from the previous year. So when we planted the cover crop, we added carbon to the mix by including triticale.”

The fall of 2022 cover crop following corn also included berseem clover and Seven Top turnips. Birdsong likes this variety of turnip because of its broad leaves that intercept raindrops and its taproot that breaks compaction while not interfering with planting. 

He varies the mix in response to how weather conditions combined with biological soil life have sped up or slowed down the decomposition of surface residue.

Assuming normal conditions, Birdsong typically follows corn with a five-way cover crop mix comprising two grasses, such as triticale and oats, one legume like crimson clover or berseem clover, and then two brassicas, such as turnips or radishes.

Following corn, he plants soybeans into the green cover crop starting in mid-April and continuing through mid-May. “We can plant soybean varieties ranging from Group 6 to Group 3,” he says.

Soybean harvest starts in mid-August with early-maturing beans to late November with later-maturing beans.

As with corn, he plants a cover crop right after the soybeans are harvested. Because of his region’s relatively mild winters, he can plant cover crops in November and still get good stands by the time he plants corn in late March or early April.

“But if we’re still harvesting soybeans by the first of November, we’ll aerial seed the cover crop into the standing soybeans and harvest over the top of the cover crop,” he says.

As with the cover crop mix following corn, Birdsong adjusts the cover crop species planted after soybeans according to the amount of surface residue he finds in soybean fields before harvest. Under normal conditions, he typically plants the five-way mix he plants after corn.

Triticale has become a staple in Birdsong’s cover crops. He tried cereal rye but now replaces the rye with triticale. He finds triticale easier to work with when planting cash crops into green cover crops, which he says is easier than planting into dried-out, desiccated cover crops.

When growing rye in the cover crop mix, he found he had to terminate the cover crop well in advance of planting cash crops.

“In our part of the country, cereal rye goes into its reproductive mode right about when we’re ready to start planting crops,” he says. “The pollen from the plants plugs the radiators on the tractors. To avoid that, we found we had to terminate the rye by mid-March, and then we found it hard to plant into the tough, dry residue.

“Triticale, on the other hand, takes longer to mature,” he notes. “Here, it enters its peak reproductive stage in early to mid-May. Usually, that lets us plant into the green crop and terminate it afterward. We also find that triticale produces good aboveground residue, and the residue lasts longer than rye residue.”

Birdsong terminates the cover crop within 48 hours of planting, either before or afterward. “The weather determines whether we spray ahead of the planter or behind it,” he says. “If the weather forecast is calling for rain, we might spray ahead of the rain and then plant. We don’t want to spray on the same day as it’s raining.”

While corn and soybeans comprise the main cash crops on Birdsong’s 750-acre farm, he also grows about 100 acres of winter wheat. The wheat typically follows corn in the rotation.

He also grows 140 acres of triticale for his own cover crop seed.

Soil organic matter increase

Perhaps the greatest cover crop benefit Birdsong has seen is increased soil organic matter, which has improved soil structure along with soil and crop resilience.

“In 1999 and 2000, our soil organic matter was 2.1% to 2.2%,” he says. “It’s presently 5.4%. That has helped with moisture retention. The soil is like a sponge. And the soil biology makes the soil resilient. The physical structure is like potting soil, especially in the top 4 or 5 inches. The combine tracks we leave in the fall disappear in about a month.”

Changes in the soil in response to no-till combined with cover crops evolved over time. “While we saw immediate results in weed control and water retention, it took at least five years to see soil structure transforming,” he says.

Despite no participation in carbon markets, Birdsong says he values the soil carbon that comes hand in hand with building organic matter. “It’s priceless,” he says. “It increases water infiltration, reduces compaction, and improves soil resilience. All the benefits of improving soil health come back to carbon and our need to build it up along with the organic matter.”

The resulting soil and plant resilience is most evident under stressful growing conditions. “In June of 2022 we got triple-digit heat,” he says. “The leaves on nearby corn grown with tillage started curling five days earlier than the leaves on our corn. That tells me our soil retains moisture longer.”

Such resilience in soils and crops is a testament to the two decades Birdsong has invested in building soil health.

“We’re improving the quality of our soil rather than using it all up,” he says. “We’re not seeing erosion. We’re building organic matter, and our yields are staying stable or increasing without us spending more on commercial fertilizers. We’re definitely going to continue doing what we do.”