A Few Small Changes Can Help Manage Compaction

Soil compaction is a critical concern, and the larger equipment becomes, the more important it is to pay attention to its potential long-term impacts to crop productivity and the environment. 

An Iowa State University (ISU) survey revealed 59% of farmers are concerned about the impact of heavy machinery in their fields, and 42% say they consider the weight of agricultural machinery when they decide on equipment purchases. 

“Farmers are aware of soil compaction, but they are also moving to bigger machinery because they want to finish their work faster with wider equipment,” said Mehari Tekeste, associate professor in ISU’s Department of Agricultural and Biosystems Engineering (ABE) and director of the Soil Machine Dynamics Laboratory (SMDL).

Equipment size has increased over the last century, with three distinct periods of growth, according to Tekeste’s research. From 1920–1940, unballasted tractor weight increased at an average 35 pounds per year. From 1990 to the present, average tractor weight per year was nearly three times the average 179 pounds per year from 1941–1989. 

“Tractors are designed to pull, and data from the University of Nebraska tractor test laboratory suggest that engineers design tractors that can pull about 50% of their weight,” Tekeste said. “So, the bigger implements coming to market require bigger tractors to pull them. What we don’t understand yet is how this heavier equipment load is spread on the soil surface, and what that is doing to soil productivity.”

Tekeste’s research shows inflation pressure strongly affects soil compation at shallower depths of 8–12 inches. Deep compaction below 12 inches strongly correlates to axle load.

“The Iowa Department of Transportation regulates axle weight on roadways at 10 tons per axle, but when equipment is being used in the field, the axle weight often exceeds that limit,” Tekeste said.

What Can You Do?

“If you have to work in conditions where the soil might be a little wet and a weaker load-bearing state, being able to make a limited number of passes with a larger piece of equipment will probably do less damage to the soil than multiple passes,” said Kapil Arora, field agricultural engineer at ISU Extension and Outreach.

However, deep compaction (16–20 inches deep or greater) isn’t always easy to notice. 

“In a year when everything is green, when we get nice rain, nobody complains,” he said. “But you are going to pay the penalty in a drought year.”

Soil compaction can be mitigated in a few ways, depending on the depth and farm operation. The best way is to measure tire-penetrated soil footprint, keep compaction as shallow as possible by spreading out the load, and take advantage of the most ideal fieldwork conditions possible. 

Tap-rooted cover crops, along with freeze-thaw cycles, help break through compaction. But these are not “one and done” solutions; it takes multiple years for these methods to ease the compaction. A chisel plow or ripper can also help to break up compaction to the depth of your points.  

Tire inflation pressure is another way to manage soil compaction. Technologies that enable simple inflation and deflation adjustments, and increased flexion (IF) and very high flexion (VF) are designed to carry greater loads at the same air pressure as standard radial tires. 

“We found that using these new tires or inflation pressure systems to inflate and deflate the tires in the field on a tractor pulling a central fill, 24-row planter, there is about a 4% gain in yield,” Tekeste said. 

Finally, paying attention to in-field traffic patterns and avoiding unnecessary traffic with heavy-axle-loaded equipment can also play a role in decreasing soil compaction.