Fragipan Yields to Cover Crops

08:02PM Nov 08, 2017
Annual ryegrass
( Darrell Smith and Mike Plumer )

Junior Upton is fragipan’s nightmare. In the late 1990s, Upton was dealing with drought and strangled yield across much of his farmland. He planted annual ryegrass following harvest, hoping to gain the conventional benefits of a cover crop and no-till system. However, the Illinois grower had no idea he’d just lit the fuse to destroy a soil scourge.

The eastern half of the U.S. is plagued by 50 million acres of fragipan soil. Light in color, fragipan often starts at 1' to 2' below the surface and roughly averages 2' to 4' in thickness. A solid barrier of cemented soil particles that slams the door on water passage and crop roots, fragipan is a yield killer. However, annual ryegrass is showing genuine promise as a battering ram against fragipan, evidenced by yield boosts and sustained success on Upton’s farmland.

Upton, 70, has farmed hills and flats since 1964, and the vast majority of his ground is afflicted with varying degrees of fragipan, hiding roughly 8" below his Hamilton County acreage. The white, chalky layer has been a consistent source of diminished yield, no surprise when grain crops subsist on the top few inches of dirt.

In 1998, Upton had a field with a notable range of scatter-gun yield. On a stretch of hilly corn ground, Upton could find an area with 125 bu. per acre yield, walk 20', and stand in a 40 bu. per acre zone. The yield spectrum spurred Upton to bring in a backhoe for field surgery. Along with Mike Plumer, a former soil agronomist with the University of Illinois Extension, and several research colleagues, Upton dug 150' across the field. The peeled layers of soil were plain to see: poor corn with fragipan and good corn without fragipan.

Upton obtained a Sustainable Agriculture & Research Education grant to trial no-till with a continuous cover crop. Plumer made a most fortuitous recommendation: annual ryegrass. His initial idea was to build soil tilth and organic matter to improve Upton’s soil quality.

“Within a couple years we really started seeing progress. I dug down in February and found ryegrass roots down 2' on a 2" plant. In just a few years, we had ryegrass roots down at 72" on 4" plants. That’s when we knew ryegrass was breaking the hardpan,” Upton says.

Fragipan is an acid soil type with a pH of 4.5 to 5.4, but ryegrass doesn’t mind the low pH, Plumer says. In wet winter conditions, annual ryegrass cracks apart fragipan by opening root channels. “In just the first year of use, we saw rooting at 24" to 28". The second year was 30". After four years rooting, was at 60" to 70",” Plumer says. In normal fragipan, soybean roots often only reach 12", but after five years of annual ryegrass, Plumer recorded soybean roots at 36".

When annual ryegrass roots die, a network of channels is left behind for corn or soybeans. A no-till system keeps the channels open as corn and soybean roots push deeper each year.

As the roots grow, the yields expand in tandem. “On Junior’s farm, we’ve got some fields 16 years in the making. His corn yields before we started were at a five-year average of 85 bu. per acre, but after six years, he was over 150 bu. per acre. After 10 years, he was over 200 bu. per acre, and it is all documented,” Plumer says.

Plumer also did on-site fertility tests on ryegrass and non-ryegrass ground. “The ryegrass went so deep and picked up phosphorus and potassium. We were doubling and tripling the phosphorus and potassium tests without making applications,” he notes.

Annual ryegrass doesn’t merely create rooting channels, it literally breaks down the fragipan, Plumer notes. The white cement material dissolves and leaches deeper into the soil. Plumer has recorded 3" of downward movement in a single year. Upton is experiencing legitimate alchemy because some of his fields don’t have much fragipan left and it has moved 30" into the profile, according to Plumer.

Annual ryegrass secretes an enzyme through its roots and can devastate soybean cyst nematodes (SCN), Plumer says. When soil warms to 60°F with annual ryegrass present, SCN prematurely hatch prior to soybean planting. Plumer noted a 50% to 90% reduction of SCN in a single year.

Plumer recommends 10 lb. to 12 lb. of annual ryegrass per acre at planting, immediately following fall harvest. In the spring, he kills annual ryegrass at 6" to 8", just before joints set and surface roots proliferate. “The No. 1 ryegrass issue I hear is, ‘I can’t kill it.’ That’s because herbicides aren’t being used correctly,” Plumer says.

“Glyphosate is neutralized by many rural water supplies. Fill the tank with water and put in ammonium sulfate. Then put in an acidifier to take the water to 5.2 pH prior to adding glyphosate. You must use treated water, or face a possible 50% to 60% reduction in efficacy,” he adds.

Annual ryegrass goes dormant below 38°F, and below 35°F it won’t take up glyphosate for three days even after a warm-up, Plumer explains: “In cold weather, glyphosate must be sprayed in the morning and must stop by 2 p.m. because it takes four hours before sunset to translocate into plants. Otherwise glyphosate will be neutralized overnight.”

Because of the success of Plumer and Upton’s work, Lloyd Murdock, Extension soils specialist with the University of Kentucky, wants to reverse engineer the process. Scientifically, he isn’t 100% certain of the mechanisms—but he’s pretty close: “It might be a chelating situation where ryegrass chemicals remove the aluminum out of aluminum silicate in the fragipan. The silicate is then free and doesn’t have anything to cement it together. Instead of cemented particles bonding, you end up with individual particles that make soil.”

Encased in plastic, Murdock takes fragipan cores and grows annual ryegrass overtop in a greenhouse setting. In the first round of annual ryegrass, changes are minimal. However, in the second and third rounds, the fragipan begins to break down and change color. It continues to change more of the fragipan with each planting.

Murdock has located fields in Kentucky where annual ryegrass has been grown as a cover crop or for cattle feed. When compared with nearby fragipan fields, Murdock observes an extra 5" to 6" of soil that was formerly fragipan.

Murdock is ramping up research and has established strip trials in three Kentucky fields. He’s also performing chemical compound research with annual ryegrass to accelerate fragipan breakdown. Four chemicals show promise: potassium chloride, potassium sulfate, sodium nitrate and sodium fluoride. He hopes these compounds, when surface applied, will follow pores provided by annual ryegrass and travel through the soil profile with enough concentration to attack underlying fragipan.

Based on 2017 harvest results, Murdock hopes to lay out the evidence to point producers to the economic boost at stake: “Put economics to what Junior has done and it shows he broke even after four years with $4 corn. From that point forward, he made money, and by year 15, the difference was outstanding. Over a 15-year period, he cleared more than $1,000 per acre on the field than he would have by leaving it alone.”

Back on his Illinois farm, Upton simply advises others to examine his ground. “I was 20 bu. below and now I’m 30 bu. above the county average, but I can’t stand anyone to think I’m bragging. I sure understand if people don’t want to listen to my words, but they can look at my soil,” he says.