Reducing inputs and increasing yields through cover crops

Despite his adoption of no-till and cover crops, subsoiling was a practice Jason Carter never questioned. Like many farmers in his region, the Eastover, South Carolina, corn, wheat, and soybean grower found spring subsoiling necessary to break up “the hardpan caused by earlier years of tillage,” he says.

However, lush cover crop growth in 2014 — his second year growing cover crops — foiled his plans at corn-planting time and changed his views on subsoiling.

“As I’d done before, I intended to subsoil and plant all in one pass,” says Carter, “but because of the lush cover crop, I couldn’t get enough traction to pull the subsoiler.”

He made only one subsoiling pass through the field. Then he dropped the subsoiler and simply no-tilled into the green cover.

“At the end of the year, there was no yield difference between the two field treatments,” he says.

He decided to drop the practice, but in 2015 a historic rainfall severely compacted soils and caused him to subsoil again out of necessity.

Nevertheless, his whole-farm adoption of cover crops has let him use the practice sparingly while reducing inputs to the barebone levels that set him apart from the norm and put him in demand as a presenter at farm conferences and field days.

Reducing inputs while maintaining yields, Carter — named a Soil Health Champion by the National Association of Conservation Districts — grows non-GMO crops on 1,000 acres, with 400 acres irrigated. He has planted a cover crop on every acre annually for the past 10 years. Reducing commercial inputs while maintaining yields is key to the profitable farm economics that drive his commitment to regenerative agriculture.

“Growing cover crops has helped me reduce my applications of synthetic nitrogen by 75% and my applications of chicken litter by 50%,” he says. “I have not used lime, commercial phosphorus, and potassium in the past eight years. I’ve reduced herbicide use by 50% and insecticide use by 75%. And I haven’t applied fungicide in seven years.”

Carter plants corn in April into a green cool-season cover crop planted the previous fall. “The cover crop consists of five to seven species, typically cereal rye, crimson clover, arrowleaf clover, hairy vetch, winter peas, and one or two brassicas like African cabbage,” he says. “These species all overwinter, if the temperature doesn’t get below 20° F. The rye will be 5 to 6 feet tall at corn-seeding time.”

Carter terminates the cover crop by rolling while planting corn.

“We have a roller-crimper mounted on the front of a 12-row planter,” he says. “We still have to come back with an herbicide to finish terminating the cover crop, but we can trim the application by 50% of the recommended rate.”

He harvests corn in August, and on dryland acres destined to be planted to winter wheat as the next cash crop, he plants a warm-season cover crop. That cover crop typically includes buckwheat, cowpeas, and sunn hemp. He plants wheat in mid- to late November, after the cover crop has winter-killed.

After harvesting the wheat in early June, he plants some wheat fields to an early-maturing soybean. “I can get the soybeans off by the first of October and still have time to plant my winter cover crop after the soybeans,” he says.

He plants other wheat fields to another warm-season cover crop. “I plant this cover to build soil biology,” he says. “I’ll roll it down the first of September, and then two or three weeks later, I’ll plant the cool-season winter cover crop.” He plants some soybeans into this terminated winter cover crop in early May.

While Carter has found the roots of the cover crops help reduce the compaction common to his coastal soils, his cover crop/no-till system was overwhelmed by the historic rain that hit the farm in 2015.

“We had 20 inches of rain in 24 hours, and the flooding compacted the soil and killed the soil biology because of a lack of oxygen,” he says.

Subsoiling seemed inevitable. Yet the following year, Carter still tried to get by without it to avoid the pitfalls of the practice.

“Any type of soil disturbance causes problems with soil biology or rebuilding it,” he says. “Subsoiling requires a larger tractor and increases fuel use by two to three times more than if you weren’t subsoiling.”

Without subsoiling after the big rain, though, Carter experienced yield losses of 20 bushels per acre or more. This prompted his decision to return to the practice.

After five years, he stepped back from subsoiling across the farm and now subsoils only a third of his land every year. To minimize soil disturbance, he uses a machine with narrow shanks and narrow points. “You hardly see surface disturbance,” he says.

With Carter’s persevering commitment to no-till planting and growing diverse cover crops, earthworm populations in the soil have rebounded while soil organic matter continues to increase.

“Our soil organic matter has grown from 0.6% in 2012 to our present level of 2%,” he says. “I believe it’s hard to build organic matter in warm climates like ours because our soil biology is constantly working. You can see it in our aboveground residue, which breaks down relatively quickly.”

Livestock Grazing

To potentially accelerate the building of organic matter and carbon in the soil, Carter is evaluating the effect of integrating livestock grazing into the cropping system. He is collaborating with the University of South Carolina and the South Carolina Forage and Grazing Lands Coalition to study the effects of grazing on his operation.

“After just one year of research, we’re seeing organic matter and soil fertility increasing a lot faster than with cover crops alone,” he says. The researchers evaluated the effects of cattle grazing a winter cover crop from February to April. After that grazing period, they planted a summer crop and brought cattle back to graze that cover crop for another 30 to 60 days.

If future research indicates continuing benefits to soil health from grazing, Carter will consider custom grazing to integrate livestock more widely across the farm.

While livestock grazing may indeed speed up the building of soil health, more than a decade of growing cover crops has already built the organic matter and biological soil life needed to reduce commercial inputs while maintaining yields.

Regenerative Ag Is the Future

“If I’m going to continue farming in the future, I know that [regenerative farming] is the way I have to farm,” says Carter. “While this system might indeed build soil carbon and benefit the environment, I farm this way because of economics. I’m able to reduce commercial inputs because the biological life releases nutrients in the soil. That lets me cut costs while maintaining yields.

“Regenerative agriculture is the future of farming,” he says. “We’re putting our faith in biology rather than the chemistry of chemicals.”