Why did we sponsor a study to explore the connection between tire pressure and yields? Because we already know that overinflated tires cause excessive compaction in the field. And compaction is stealing your profits. In fact, it’s probably one of the biggest profit-stealers on your farm. Research has shown that soil compaction can slash yields by up to 15% in a single year. It can also affect your yields for over a decade—even with tillage and no additional compaction.

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Learn More: How compaction is costing your farm + 3 steps to fight back.

What Happens When You Give an Agronomist a Tire Pressure Gauge?

This probably sounds like the beginning to a bad standup routine, but the results were eye opening. When he called on farmers to talk about their 2021 agronomy plans, Nate Firle brought a tire pressure gauge along in order to conduct an informal experiment. The first question he asked each farmer was, “Do you know how much air is in your tractor’s tires?” Nearly everyone replied as expected: “What does that have to do with anything?” From there, though, the results became much more interesting.

A Startling Discovery . . .

Firle found that 70% of the farmers he asked didn’t know the pressure in their tires. Of that 70%, 20% did say that they have someone come to their farms to help set up their equipment for fieldwork. Or, they have the proper tire pressure written down somewhere and will check their tires before heading out to the field.

Outside of the 70%, a full 20% of the remaining growers knew exactly how much air was in their tires: whatever was printed on the tires’ sidewalls (the maximum inflation pressure). This is a great roading pressure (or pressure for seating the bead), but not what you want to be running in the field. 

Only 10% of the farmers Firle visited knew exactly how much air was in their tires—and why. 

For Firle, this was an eye opener. These conversations confirmed the need to do a study on tire pressure and its potential effects on yield. 

Our Study Design: From Road Pressure to Low Pressure

So, back to our question: would you see a difference in yield if you ran different tire pressures on your equipment during planting? In order to answer this question, AgRevival designed the following study:

Test Equipment: John Deere 7280R Tractor & 8-row 1760NT Planter

The tractor weighed 34,000 pounds while the planter clocked in at just over 6,000 pounds. While the tractor's weight could be considered 'typical' for a large-scale farmer, the planter was still significantly lighter than a large central-fill planter. The planter was weighed down with full seed boxes and two full liquid tanks for each test run to get as much weight as possible on the ground. This planting setup was used for both corn and soybeans.

5 Tire Pressures Tested (35 psi–6 psi)

The study tested five different tire pressures (35 psi, 28 psi, 20 psi, 12 psi, & 6 psi). The tractor fronts, tractor rears, and planter tires were all set to the same pressure for a particular plot. Firle chose a wide pressure range to reflect the growers who were running their tractor tires at roading pressures in the field (the 35 psi group) all the way down to more ideal and super-low pressures.

300-Foot-Long Test Plots, Replicated 6 Times

Test plots measured 8 rows by just over 300 feet long. Each tire pressure test plot was replicated 6 times. So in total, there were 30 test plots (5 tire pressures replicated 6 times) for corn and 30 test plots for soybeans across 7 acres of new ground.

Center 6 Rows Harvested from Each Plot

During harvest, only the center six rows from each plot were harvested. Why? Because we wanted to harvest only rows affected by tire traffic—the rows between or next to a tire.

3-Year Study over Same GPS Lines

The study is designed to run three years. For years two and three of the study, the exact same tire pressures will be run over the exact same GPS lines. This is to test if tillage (a V ripper in fall and field cultivator in spring to prepare the seed bed) would take care of any compaction, or if we’ll see a larger yield decrease on the high-psi test plots.

Another NTS Tire Supply Study: LSW super singles can help take the pressure off your soil and may deliver a yield bump.

A Cautionary Tale on Yield Data

“I don’t like making drastic decisions off year one data,” remarked Nate Firle of AgRevival. “It’s a needle pointer. It shows that this is a direction we can focus on for the next year of the study.”  In other words, year-one data is a foundation to build on—not an absolute answer. It’s helping us build an understanding of the relationship between tire pressure and yield, which will continue to grow as the study progresses. So, how intriguing were the results we saw in year one?

Lower Tire Pressures Brought Higher Yields

The first year of our study showed a yield increase each time we reduced tire pressure on both corn and soybeans. You can see for yourself on the charts below. With soybeans, we saw a yield bump at our first tire pressure drop to 28 psi; with corn, we had to drop the pressure to 20 psi before we saw any yield benefit. Overall, the most interesting result of the study is that we saw a yield increase with every incremental decrease in tire pressure. 

Why? Firle speculated that the positive yield expressed in both corn and soybeans at the lower psi is directly related to the early season development of the crops tested. Compacted soil, with poor aggregation (or structure), brings many negative effects, including poorer root development, which will affect yields.

Lower Pressures = Larger Footprints

During the study, we also took the time to drive on to whiteboards with spray painted tire lugs at the different tire pressures, which became the most powerful visuals from the testing. “You think that you squat out, but you really lengthen the footprint,” said Firle. “You don’t know how much that is until you capture it.” As you can see here, lowering the tire pressure resulted in a much longer tire footprint. Between its 8 tires (duals front and rear), the tractor gained more than 1,200 square inches in footprint area from the highest to lowest psi. The planter's footprint on the ground more than doubled.

Lower Pressures = Less Slip, Better Fuel Economy

Prior to the study, the test tractor underwent a SmartSwap™ changeover to VF-rated front and rear tires, which made running the ultra-low pressures safe for this planting setup*. According to Firle, he noticed several benefits to the tire change: One, slip was consistently lower than with his previous tire setup. Because of this, the tractor’s fuel economy was greater: “It was making us more money.”  And, as a side note, Firle felt that the tractor’s handling and ride were also greatly improved. 

*Always set your tire pressures according to your tire manufacturers’ recommendations based on load and speed.

Looking Forward to Study Years 2 & 3

“I hope we don’t have adverse conditions for the local farmers,” remarked Firle, “but from a research standpoint, seeing some extremes might be of some benefit.” Other than some dishing of the soil following planting at the higher psi, Firle didn’t observe any physical signs of compaction in the test plots. But the weather conditions during the spring of 2021 were some of the best on record. You may be wondering, if the weather turns wet, are we going to see more physical issues—and larger yield decreases—with higher tire pressures? “Stay tuned is what I like to tell growers,” says Firle. 

The Best Advice to Farmers for Right Now

“Look at your psi . . . have an understanding of what you’re running in your tractor, sprayer,” says Firle. “What makes us money? It’s the crop, not getting a piece of equipment to and from the farm.”  Every pass counts. What do you need to do to optimize your machine’s footprint in the field to ward off compaction and yield loss? Take a 1,600-gallon sprayer on narrow tires, for example. How do you spread that weight out a bit? Firle’s recommendations square with our own: To start, you need the right tires set to the optimum tire pressure for the task at hand. And in some cases, tools such as a central tire inflation system may pay dividends for your farm.

You might like: Use a central tire inflation system to avoid applying excessive compaction with your sprayer.

Want a closer look at AgRevival’s 2021 research studies? You can download the 2021 AgRevival Research Book and review more than 20 replicated trials conducted across 440 acres. Want to decrease compaction in your fields, burn less fuel, and enjoy a better ride and machine handling? The right tires will make all the difference. Call and talk to one of our tire experts to drive your farm forward in 2022 and beyond.