“Erosion,” says Mike Hubbs, “is a symptom of poor soil health, the soil’s ability to function.”

Hubbs and Greg Brann, specialists with the Tennessee Association of Conservation Districts, discussed and demonstrated how cover crops and crop rotation improve water infiltration, reduce erosion and runoff, and improve or maintain soil health at the recent Milan No-Till Field Day.

The 30th annual field day, hosted by University of Tennessee Agricultural Research, featured 16 plot tours covering multiple aspects of no-till practices in row crop and forage systems.

Cover crops, Hubbs says, make up an important part of the equation and “prevent a drop in the soil biology cycle.” That cycle includes plants that absorb energy from the sun and convert it into sugars (carbon) that leach into the soil. “Organisms in the soil eat on this biology,” Hubbs says. “Green plants increase the amount of soil biology.”

See also: 30th Milan No-Till Field Day offered ample evidence of the value of conservation tillage

Healthy soils include organisms, such as earthworms, that crawl through the soil, ingesting nutrients and leaving fecal matter behind.

“Tillage breaks down those soil aggregates,” he adds, “and exposes soil to bacteria, which reduces carbon. Along with erosion, tillage results in soil aggregate loss.”

It’s best, he adds, “to keep green plants growing on the soil as much as possible. Continuous green growth and root growth feed the carbon system. Consistency is important to maintain soil health.”

 Soil Biology

He says organisms, such as earthworms, bacteria, fungi and protozoa, live near plant roots and feed on plant exudates that leak out of the plant’s “plumbing system. They feed on exudates — carbon, protein, sugars (also a carbon).”

From 5 percent to 25 percent of the plant’s carbon will leach into the soil, he says.

Hubbs emphasized the importance of soil health with an alarming figure. “Since the 1950s, we’ve lost 50 percent of soil carbon across the United States.”

He says soil health improves water infiltration. “Milan, Tenn., averages 52 inches to 54 inches of rainfall a year. That does not always come in equal intervals—we sometimes have intervals of drought, such as 2016—but this year moisture is coming in pretty good intervals.

“Consequently, we may not see much difference in soil treatments this year, but we want to continue to improve the water cycle.”

 Organic Matter Benefits

Organic matter enhances the process. “We need something to help bridge the gap during drought intervals,” Hubbs says, “by bringing more water into the soil structure. If we can infiltrate 95 percent to 98 percent of the moisture, we maintain the cycle. As soil carbon goes up, we hold more moisture.”

See also: Successful use of cover crops may require seed treatments

He says a 1 percent increase in organic matter means the soil will hold another 27,000 gallons of water. “If we build it, it will come,” he said. That includes earthworms, aggregate stability, nutrient cycling and other soil health advantages.

“But be patient. Before soil organic matter goes up you may see cost savings, you may add a cover crop, you may apply reduced tillage. Be consistent. It takes time.” The advantages will come, he adds.

He says no-till, without a cover crop, will create some soil plating. “We can do a better job with a cover crop. We can lose soil stability in just one year without a cover crop.”

He says combinations work best. “With just legumes, we don’t maintain the aggregate. We want a good mix.”

Hubbs turns to a sports metaphor to explain the value of residue and cover crops. The first step, he says, is defense. “That’s the old crop residue that insulates and cools the soil, providing cover and a food supply for soil organisms.

“Next, we have to keep disturbance to a minimum — no-till. Tillage breaks down the aggregate.”

Hubbs says the offense takes over by planting a cover crop. “Just after harvest, seed the cover crop. We want to shoot for 24/7/365 with something green on the soil. We want diversity in the mix, plants that die at different times and with different root systems.”

Consensus among presenters is that planting cover crops with a drill is preferable to broadcast. “With broadcast, we are successful about half the time,” Brann says. “Drilling takes more time, but it’s the best way.”

They also note that aerial seeding is an option, but timing is critical — as soybean leaves begin to yellow. Hubbs says if seed is applied while soybeans are green, the bean plants will take moisture and the cover crop will struggle to germinate and grow.

 Rainfall Simulator

Brann used a rainfall simulator to demonstrate the advantages of cover crops and other surface residues. “We don’t want runoff,” he says. “We don’t want flooding. We want water infiltrating into the soil.

“Tillage creates the most disturbance and leaves less soil aggregate,” he says.

“Some farmers have said they need tillage to get water into the soil,” Hubbs says, “but that creates runoff and lost soil.” Tillage causes the soil to seal and prevents infiltration, he adds.

The rainfall simulator trial consists of five treatments, ranging from vertical tillage to no-till with corn, a soil health mix cover crop, and soybean rotation. Treatments include a control with no-till and corn/soybean rotation; corn, rye, soybeans; corn, rye, crimson clover; and corn, soil health mix (SHM) cover crop, and soybeans.

“Heavy residue,” Brann says, “results in little runoff and good infiltration.” He turned on the rain simulator, let it run for a few minutes, then examined containers underneath each treatment and jugs in front of each that collected runoff.

 Infiltration Gains

Vertical tillage showed little infiltration, and the runoff collected was muddy. The control, with some residue on the surface, showed improved infiltration but still some dingy runoff. The treatments with cover crop and rotation showed significant infiltration and limited runoff, mostly clear. The soil health mix, which consists of grasses, legumes and brassicas (turnips, radishes, etc.) showed the best water infiltration and the least amount of runoff, which was almost clear.

“When rain falls on unprotected soil, it splatters and scatters soil particles,” Brann explains. “That moves soil off the field and reduces production potential.”

See also: ‘Silent killers’ robbing soybean yields

He adds that erosion also results in reduced soil nutrient levels. Cover crops create “macro-pores and root channels and encourage earthworm and other organism activity. We get a lot of openings for infiltration.

“We can design a system to manage where the water goes,” Brann says.

The soil health mix includes cereal rye, oats, radish, crimson clover and hairy vetch.

“Grass is even a step above the soil health mix,” Brann says. “The higher the organic matter, the more water it will hold.”