Fighting Compaction: Tread Lightly

When Al Sheahan purchased a 12-row corn head last year to replace the six-row head on his combine, he had more than increased capacity in mind. He was also taking one more step toward implementing a controlled traffic farming (CTF) program and reducing compaction on the 2,800 acres he farms in partnership with neighbor Todd Myren near Nelson, Wis.

Now, by doubling the size of his corn head, Sheahan calculates that, even if he has to drive slower to accommodate greater header capacity, he will make half the number of trips over the field. “That also means half the tracks, since I’ll be able to harvest 12 rows while using the same wheel tracks,” he says. “Plus, it lets me increase productivity, so I can’t help but think it will pay off.” 

Improving Yields

CTF systems, which have been more prevalent in Canada, Europe and Australia, are now gaining additional converts in the U.S., and for good reason. Research in tilled soils shows approximately 75 to 80% of the increase in soil density and 90% of wheel sinkage—both of which can ultimately limit plant growth—are caused during the first pass. However, CTF can limit the compacted area to less than 15% of a given field, compared to more than 50% from some uncontrolled traffic systems, in just one season.

The benefit is to a farmer’s bottom line. Australian research over 20 years has shown CTF can improve grain quality and has the potential to increase grain yields by 2 to 16% (10% is a common average after the year of establishment) if there are no other limiting subsoil constraints.

There are other benefits, including improving fuel and other input efficiencies. Yet, CTF often requires an investment of time and money on the front end. For instance, Sheahan and Myren have, over the years, purchased a variety of equipment that allows them to confine their footprint to the fewest traffic lanes. “Because all of our machines are set up for GPS-guided autosteering on an RTK system, we can use the same wheel tracks for just about every pass,” says Sheahan.

“A lot of our equipment already fits a 30-foot pattern, so the combine [head] was just the next step,” Sheahan says of the Massey Ferguson® 8780 he bought used. “We try to plant no-till as much as we can and limit any other tillage to vertical tillage or a field cultivator. Still, our tillage equipment is 30 feet wide; our 12-row planter covers 30 feet; the sprayer covers 60 feet; and our RoGator,® which we use to apply liquid nitrogen, spans 90 feet.

“We have everything set up for 30-inch rows, with four rows between the tires on just about every machine,” he explains. “We realize, of course, that there will be more compaction on those wheel-track rows, but at least it will be limited to those rows.” 

Heavy Hitters

One of compaction’s chief culprits is increasing equipment size. In the 1940s, the average weight of tractors on the market was about 3 tons. Today, it’s not uncommon for high-horsepower tractors and combines to weigh 20 tons or more.

That’s one reason Sheahan has dual wheels on the combine and all of his tractors; he also uses them because they increase stability on the steep hills he and Myren farm. However, they can be both a help and a hindrance, according to Conor Bergin, AGCO tactical marketing manager for application equipment. Granted, duals provide a larger total footprint and greater flotation, but they also increase the “pinch point,” says Bergin, that leads to even more compaction.

“Anyplace there is a tire footprint, you’ll see some compaction to the side of the tire track,” Bergin explains. “That means the greatest yield losses occur in the row or area between tractor duals where the pinch points meet together.”

The key for duals and single tires, he adds, is inflation pressure. In one Ohio State University study that compared duals with tracks, overinflated duals caused the most compaction. However, the trial also showed that duals can do as good a job in avoiding topsoil compaction as tracks, provided the tire pressure is kept low.

One of the best ways to prevent compaction is to stay off the field until it’s dry enough to work. Bergin explains that any soil type can be compacted. However, it’s the water-holding properties of the soil that make the most difference. Increased moisture leads to deeper compaction, as do increased axle loads. 

The Balancing Act

There’s not a hard-and-fast set of rules governing compaction. Sometimes the severe economic repercussions of delaying planting, harvesting and other operations can outweigh compaction damage or loss. Jim Enyart, field engineer for Trelleborg® Wheel Systems Americas, Inc., a major supplier of tires for AGCO tractors, says farmers are also forced to compromise when it comes to tire pressure.

“It’s a proven fact that reducing the air pressure in a radial tire increases the footprint, which helps reduce compaction,” he says. “But you don’t want to reduce pressure to the point that it will cause damage to a set of tires worth several thousand dollars, especially when you pull out of the field and head down the road.

“There’s also a fine balance between too much air pressure and tire slippage. Tire slippage by itself can cause as much or more compaction as the tire spins and packs the soil.”

However, recent axle innovations can help reduce compaction. For instance, says Bergin, “the front-axle suspension system on Massey Ferguson and other AGCO tractor brands ensures better tractive ability, reducing slip, which in turn reduces compaction.”

According to Sheahan, such a front-axle system has proved quite helpful on the Massey Ferguson 8670 that he and Myren use in their operation. Among other benefits, says Sheahan it allows them to reduce air pressure in the tractor’s tires.

“If you looked at the tires, you’d think they were going flat,” he says. “It’s just another way to reduce compaction. Because of our hills, we no-till almost everything to reduce erosion, so there’s always a trade-off somewhere.”

With a knowing grin, he adds, “You just have to hope the weather lets you work it out.”

Why Compaction Is Harmful

“Heavily compacted soils contain few large pores and have a reduced rate of both water infiltration and drainage from the compacted layer,” says John Moncrief, Extension soil scientist with the University of Minnesota Extension Service. “In addition, the exchange of gases slows down in compacted soils, causing an increase in the likelihood of aeration-related problems.

“Finally,” continues Moncrief, “compacted soil means that roots must exert greater force to penetrate the compacted layer. This, in turn, can decrease the plant’s ability to take up nutrients and water, which can ultimately result in a yield reduction.”