Editor’s Note: This Q&A originally appeared in AG Tire Talk to provide answers that farm equipment dealers have about farm tire technology. This series features a trending question followed by an abridged version of the answers. For the complete answers, check out www.agtiretalk.com.

How much soil compaction (percentage wise) is typically done on the first pass, what are recommended tips relative to defining traffic paths (easy operator changes) and run conditions (dry or wet) to reduce soil compaction, and do you have recommendation on penetrometer usage to determine level and depth of compaction?

AG Tire Talk Takeaways

YOKOHAMA: (Alliance):  Soil compaction can have a huge impact on crop yields … Tires are actually a key part of the solution. It’s actually easy to figure out—soil compaction force is usually close to a tire’s inflation pressure, so a VF or flotation tire running at 12 psi causes about half as much compaction as a conventional radial running at 25 psi.

BKT: For soil to be healthy, soil particles and pore spaces should be close to 50/50%. When pore spacing is decreased, air and moisture are driven out of the soil. The soil density increases. Research has shown that 70%-80% of compaction is done in the first pass.

MICHELIN: “As a percentage, how much of your soil surface is touched by rubber in a normal annual farming cycle?” … about 90%. There are different theories as to how a producer can avoid this issue. One idea is to simply follow the same tire tracks whenever possible- i.e. following the combine tracks with tractor/grain cart.

PRECISION INFLATION: Bottom line, IF the field is too wet, stay out.  IF you go into a marginal field, understand you will be damaging your VALUABLE soil and taking a yield hit for several years.

MAXAM: Tire Tip #2: Use a penetrometer to accurately track soil compaction in your fields. A penetrometer is a tool that will allow a farmer or grower to determine the amount of soil compaction on his field. A penetrometer can help determine how machine loads or axle loads are impacting ground pressure and the resulting soil compaction.

CONTINENTAL: The first passage with your equipment; in muddy, swampy, or post storm conditions, can compact the clay/loam type soil almost to the maximum level.

BKT USA, Inc.

Dave Paulk: Manager Field Technical Services

Soil compaction can reduce plant growth, root penetration into the soil and root size. Soil becomes compressed (compacted) through agricultural practices, cultivation, and wheeled traffic. It restricts water and air distribution in the soil. This can result in a lack of water and nutrient distribution and can cause slow seed emergence and diminished crop yields.

For soil to be healthy, soil particles and pore spaces should be close to 50/50%. When pore spacing is decreased, air and moisture are driven out of the soil. The soil density increases.

Deep soil compaction is of greater concern than near surface compaction.  Soil compaction can be managed and minimized. Prevention of compaction is better than trying to repair it. Once compacted, it can take years to undo the damage.

Research has shown that 70%-80% of compaction is done in the first pass. Compaction can vary depending on the soil type, soil moisture, tire size, air pressures, and total loads. With conventional tillage, research has estimated that 90% of a field can be tracked on during the year. By cutting down on the traffic in a field, compaction can be managed, and the subsoil allowed to regenerate.

If possible, farming operations should not be done on wet soil. If the soil is near saturation, the load can be greater than the soil’s ability to support it causing deep ruts and excessive wheel slippage. Heavy fertilizer spreaders, combines, grain carts, and trucks can be destructive on overly wet soil. Improving drainage can reduce having to work in wet fields.

It is much better to work in dry or moist soil. Managing traffic paths and patterns and using only portions of the field for traffic can help manage compaction by not driving on it. Tramlines can be used for sprayers and implements to reduce late season damage to plants which are small field roads created at planting by preventing seeds to fall into those rows.

Using a penetrometer can measure the force needed to insert a cone into the soil. It is inserted by hand at a steady speed to determine the force required to penetrate the soil at a certain depth. The measurement is generally given in megapascals (MPa). Generally, root growth becomes affected when resistance exceeds 1.5 MPa. Root growth is severely restricted at 2.5 MPa or more. Deep soil compaction is excessive compaction below the normal tillage depth. Generally, this starts at about 8 inches depending on the type of soil. 

Michelin Ag

David Graden: Operational Market Manager – Agriculture

During speaking engagements, I like to ask my audiences, “As a percentage, how much of your soil surface is touched by rubber in a normal annual farming cycle?” Most of the time, the answers will range between 15% and 65%. I then point out Spring fertilizing, tillage, planting, spraying, etc., whereas I begin to see a few Aha faces in the audience. Finally, I give the answer of about 90%.

From a soil standpoint, every pass of a machine contributes to more and more compaction. The first pass of a machine will contribute to shallow compaction; however, repeated/overlapping passes contribute to deep compaction, which will eventually lead to “hard pan soil.” Hard pan is a layer of soil that is impermeable to water and needed oxygen, thus hindering the development of yield. In fact, if the soil has a higher moisture content, the soil compaction damage is even greater, due to the liquid state of the soil drying into a solid.

There are different theories as to how a producer can avoid this issue.  One idea is to simply follow the same tire tracks whenever possible- i.e. following the combine tracks with tractor/grain cart.  Additionally, taking the grain load process off the field has major impact on field ends as tractor trailer high pressure tires with exceedingly high weights coupled with existing multiple tire track soil compaction can easily result in difficult to remedy hard pan.

Another idea is to create or use controlled traffic paths. By following the same tracks on every pass, you could remove all impact from most of the ground and focus all of that compaction into a limited number of tire tracks crossing your field. The downside is, you may have to purchase new equipment with matching widths, so all machines cover the same number of rows.

Another idea is to outfit your machine fleet with Michelin Ultraflex (VF) tires. Independent studies at Harper Adams University in the UK and the University of Illinois – Campaign Urbana have proven a yield gain of up to 4.31% using properly inflated Michelin VF tires vs standard radial tires. Compared to controlled traffic paths, producers wouldn’t have to sacrifice the ground in which they used for their designated tire tracks. This means, improved efficiency, higher yields and a much faster return on investment.

Finally, if you think soil compaction has or is hindering the root development of your crop negatively affecting your yield, you could use a cone penetrometer. A cone penetrometer is a tool used to measure and record the downward force required to penetrate different layers of soil at different depths. This measurement is usually recorded in pounds per square in (PSI). In general, studies have shown a restriction in root development when the penetration resistance exceeds 50-75 psi and severe restrictions or nondevelopment at 75 psi or more. In fact, PennState Extension published the following table to simplify things for users.

Yokohama Off-Highway Tires America

Blaine Cox

Soil compaction can have a huge impact on crop yields, soil health and water infiltration, and it’s something farmers can help minimize through careful tire selection and maintaining the proper inflation pressure. Tires are actually a key part of the solution.

It’s actually easy to figure out—soil compaction force is usually close to a tire’s inflation pressure, so a VF or flotation tire running at 12 psi causes about half as much compaction as a conventional radial running at 25 psi.

Jodi DeJong-Hughes at the University of Minnesota — a speaker at the 2022 National Strip-Tillage Conference  — and her colleagues calculated an average yield loss of 21% in corn and soybeans for two years after compaction damage was caused, and she talks about one field she studied in Minnesota that suffered yield losses for 13 straight years after a single wet harvest.

Compaction isn’t just isolated to the ruts you leave at planting with your tractor. Researchers at the University of North Carolina determined that 50% to 85% of the area of a corn field gets rolled over by at least one piece of equipment during a season. That’s why Yokohama Off-Highway Tires America is so committed to our Whole Farm concept, which is a commitment to offering low-inflation pressure tire not only for heavy tractors, combines and grain carts, but for all the machinery that farmers use, including sprayers, seeders, tillage equipment and other implements.

We talk with farmers about the importance of selecting low-pressure options for as much machinery as possible, whether it’s one of our Alliance Agristar+ VF radials, our fast flotation radials that can be towed at highway speeds, or any of our other IF, VF or flotation tires. We also strongly emphasize the importance of operating at the lowest appropriate inflation pressure for the load and speed of operation.

Central tire inflation systems (CTIS) will really help with that as they become more common, because they make it possible for farmers to adjust between lower pressure for fieldwork and higher pressure for road travel by just pushing a button—and they help your tires last longer, too. But right now, many people just operate at low field pressure and drive more slowly down the road so they can protect their soils from compaction.

But at the very least, we encourage them to avoid working in fields that are too wet. What’s too wet? I like the old trick of making a ball of soil in your hands like you’re making a snowball, maybe the size of a walnut or an 8-ball. Toss it a few inches in the air and let it land in your palm. If it breaks apart, you should be good to go. If it sticks together, it’s too wet to work—driving on that field will cause soil compaction for sure. 

Precision Inflation, LLC

Ken Brodbeck, VP of Technology

How to Reduce Soil Compaction: Do’s & Dont’s

DON’T:

1. DON’T buy the tractor with the heaviest weight package with the smallest tires or tracks. Bigger tires PROPERLY INFLATED, and wider tracks, both reduce soil compaction and rutting.
2. DON’T add large fertilizer tanks to your planting tractor unless you have considered how much more tire pressure is required to carry the extra load.
3. DON’T assume tracks have no compaction. There are many farmers who will admit they can see stunted crops where tracks compacted the soil when soil conditions are marginal.

DO’s:

1. Depending on the planting or harvesting window, DO stay out of the field if it is too wet. (Standing water in low spots, soil works poorly and/or rutting is obvious and excessive.)
2. High Tire pressure = Higher Soil Compaction. DO set tire pressures to minimum to minimize soil compaction and rutting.
3. DO have a tire inflation system so you can stay at minimum field pressure and re-inflate for transport, thereby optimizing machine performance for both field and road AND promoting soil health while minimizing soil compaction.
4. DO remove extra cast weights from both wheel and track tractors unless absolutely necessary. Excessive Ballast = excessive tire pressure AND excessive pressure under Rubber Tracks.
5. DO reduce number of trips across the field. Fewer passes = Fewer compaction areas.
6. The passes you do make, DO keep them together to localize any compaction. Example: The grain cart should follow the same path as the combine did.

Bottom line, IF the field is too wet, stay out.  IF you go into a marginal field, understand you will be damaging your VALUABLE soil and taking a yield hit for several years.

Maxam Tire International

Greg W. Gilland, Business Development & Ag Segment Manager

In agricultural operations, the primary driver for increased crop results or yields is the impact of soil compaction on the plant’s ability to grow. Soil compaction occurs when stress is applied to a surface soil causing artificial densification or thickening as the air is displaced or pushed out from between the soil grains or pores reducing the oxygen content and impeding plant root growth. In agricultural operations when weight or load is applied, it will cause densification due to air and water being pushed or displaced from between the soil grain molecules. Therefore, soil compaction is a normal and inevitable part of agricultural operations.

Soil Compaction is impacted by the following materials:

• Initial soil pore volume (porosity of the soil / mix of soil)
• Perceived or measure water content in the soil (predominant influencer)
• Amount of ground pressure (tire footprint and air pressure caused by axle load)
• The effect of multi-passes on the same area or rows by the equipment

Ground pressure is therefore directly impacted by the tires working the field based on the below contributing factors:

• The total vehicle load per axle and number of tires
• The distribution of the load on each individual, dualled or tripled wheel position
• The tire inflation pressure per the vehicle or towed weight
• The tire GFP or “gross flat plate” or contact surface area because of tire tread dimension and lug design
• The type and weight of the selected implement in operation
• Surface soil compaction is mainly impacted by the tire footprint pressures (ex: the larger the footprint, the lower the pressure)
• Deep soil compaction is the resulting function of utilized equipment weight and repeated passes but is largely impacted as well by the type of soil and moisture content

Proposed Solutions to Reduce the Impact of Soil Compaction:

A widely accepted solution is a “traffic or controlled path plans”. Controlled path plans are precise traffic lanes designed to reduce soil compaction by restricting the powered elements of the equipment to travel over exact rows for repeated passes.  

Tire Tip #1: Utilizing the right tire size, at the right air pressure to increase your tire footprint will result in reduced ground pressure or soil compaction = greater yields!

Tire Tip #2: Use a penetrometer to accurately track soil compaction in your fields.

Tire Tip #3: The most critical consideration to reduce compaction is to avoid any hard tillage work when soil conditions are extremely wet.

­­­­­Tire Tip #4: Utilizing tires with a longer or larger contact areas coupled with less field passes will ensure reduced soil compaction.

Continental Agriculture North America

Harm-Hendrik Lange, Customer Solutions Engineer for Continental Commercial Specialty Tires (CST)

Many institutions and universities have been testing and assessing soil compaction for years. It is well known that soil types with high clay particle content are more prone to staying compacted and are not easily churned up with implements, like with more sandy soil types. 

When you work in wet, or partially wet, clay soil fields (or even on loam that is a mixture of different particles, but predominantly clay), be aware of the potential harm that can be caused to the soil.

The first passage with your equipment; in muddy, swampy, or post storm conditions, can compact the clay/loam type soil almost to the maximum level. It is advised not to do field work with this level of moisture, if it can be prevented. At mid to slightly higher humidity, the drastic soil compaction can happen, but here it’s more likely on the second passage or if you ride the first passage very slowly but with vibration excitation (maybe due to PTO implements that are not balanced) that can make the tractor act like a vibration plate. Tires also play a key role on soil compaction. The best advice is to run tires at the minimum required inflation pressure in order to increase the footprint and decrease the ground contact pressure.