7 ways to reduce compaction

If you want healthy soil structure (and good yields), a tire gauge may be one of the most important tools to use before planting this spring. You've carefully purchased the seed with the best genetics and the right fertilizers and chemicals to produce the best crop. You don't want compaction to compromise your results.

"Ideal soil is 50% sand, silt and clay, and 50% pore space — half air and half water. When you compact the soil you are taking out pore space," says Jodi DeJong-Hughes, University of Minnesota educator-crops. That leads to poor drainage and cooler soils more prone to diseases and anaerobic conditions — and as a result, less yields. Reducing compaction helps build soil structure, allows water to infiltrate quickly, warm soil faster and hold up under heavy equipment.

1. Adjust psi for the heaviest axle load

"It's important to set the pressure for what you are doing," says Ken Brodbeck, field engineer with Firestone Ag Tires. The ideal might be 14 psi for the tractor tires in the field, but if you are pulling a planter 5 miles on a road, the pressure needs to be bumped up to about 30 psi to prevent tire damage during transport. He empathizes with producers that it requires extra work — from taking time to weigh fertilizer tanks for an accurate weight before looking up the proper psi according to axle weight on the tire manufacturer's website, to getting down and dirty to check tires in hard-to-access places.

Plus there are variables to calculate. For example, pressure should be checked in the a.m. when it's cool. Because psi drops 1 psi for every 10 degrees, to be on the safe side, add 2 to 3 psi for possible cooler days during the planting season (for temperature drops from 70 to 50 degrees, for example).

When purchasing new tires, consider IF (Increased Flex) and VF (Very high Flex) tires that carry 20% and 40% more load with the same tire pressure, compared to standard tires, Brodbeck suggests. For example, an IF tire only requires 23 psi compared to 35 psi in a standard tire.

Radial tires also outperform bias tires — but only if they have the proper psi.

"For any farmer, tires are the most expensive replacement part," Brodbeck says, so it's important to take care of them. "Check them every week or two. Adjust tires for different work."

2. Tracks aren't a panacea

Tracks improve traction and ride-ability in the field, but a 25-ton per axle grain cart will still create subsurface compaction whether it has tracks or tires," DeJong-Hughes says. "The lower the inflation pressure the better it is to maintain soil porosity."

An Ohio research project with a John Deere 9600 tractor showed that wide tires at the correct pressure (15 psi) had less compaction than a half-track with 10 psi. Despite the low pressure in the track, the compaction was equal to a tire with 26-30 psi.

When choosing equipment make sure the tracks are no wider than the carriage so they evenly distribute all the weight. Also check the tracks for even wear. Uneven wear on tracks (or tires) indicates uneven weight distribution.

3. Stay on track

Since equipment doesn't float, there is no way to eliminate compaction. But you can manage it with controlled traffic — driving on the same path. About 80% of compaction is made on the first path, DeJong-Hughes says. Consider wheel spacing when purchasing equipment to keep everything on the same track. She admits controlled traffic requires lots of management and changes to tire configurations.

"Converting machinery to controlled traffic is not a simple change, but rather a transition that can take several years to complete," she says. If controlling all wheel traffic is not feasible, control the heaviest equipment, such as the grain cart. To reduce wheel traffic across the field, grain carts should use the previous combine tracks when possible. At all costs, avoid driving heavy equipment across the field at a diagonal.

4. Think light

Producers love their big tractors and implements to get fieldwork done quickly, and wide axles make fewer compacted wheel tracks. But weight matters.

"When at 35-40 tons you can compact soil 3 to 4 feet, with a lot of compaction in the top 12 inches," DeJong-Hughes says. "When possible use a lighter tractor to do lighter work. And don't go to the largest grain cart you can find. The risk to soil outweighs the benefits."

Pay attention to the wheel slip monitor on your GPS, adds Brodbeck. The ideal slip range is 8% to 12% for the least compaction, best traction and fuel efficiency. If it's 2% to 4%, remove wheel weights. The general rule is to lighten up for planting and put the weights back on for tillage in the fall.

5. Reduce tillage as much as possible

DeJong-Hughes and coworkers built "soil sandwiches" with layers of sand and topsoil to illustrate compaction with various tillage equipment. Because of rain causing slabbing, the results weren't as clear as hoped. Still, it made the point that the most aggressive tillage (moldboard plowing) tears up soil structure, which reduces air pores and creates compaction. It also reinforced the point about proper tire inflation. The most visual compaction was from tractor tires that were overinflated.

The "good" news from the demo was that the tillage equipment didn't go as deep as operators expected. DeJong-Hughes was especially impressed with a vertical tillage plow capable of "precision tillage" with a chisel plow that can be raised and lowered from the cab. "You don't have to go as deep on the hills," she says.

6. Ruts can heal themselves

Producers "blessed with winter" have one advantage when it comes to compacted ruts, DeJong-Hughes says. Instead of ripping wheel ruts, lightly fill them up. Within two or three years, freezing-thawing cycles will eliminate ruts up to 5-inches deep.

"It's like doing deep tillage naturally," she says.

7. Stay off the field until it's time

This is the toughest one for farmers eager to plant, but they know when fields are too wet. If wet springs continue to be the standard, farm management may need to change: add cover crops to take up excess moisture and dry fields out sooner or add light vertical tillage.

Or, just hold back to let the soil dry a little more.

"Sometimes just waiting until the afternoon can make a difference," DeJong-Hughes says. "That and having the planter in great working order, and the right tire inflation will give you the best stand."