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AG Tire Talk: Tips to Help Minimize Soil Compaction

Traffic Paths, Run Conditions Play Critical Roles

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Controlling ground pressure can help minimize soil compaction, say ag tire manufacturers.

Modern Tire Dealer has partnered with AG Tire Talk to provide answers to insightful questions that farm tire dealers have about farm tire technology. This is the next installment in our ongoing series, which is designed to help farm tire dealers better connect with their customers. A trending question, followed by answers, will appear in our Commercial Tire Dealer section every other month. For complete answers, click on www.agtiretalk.com.


Question: How much soil compaction 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 a recommendation on penetrometer usage to determine level and depth of compaction?


Dave Paulk, manager, field technical services, BKT USA Inc: Soil compaction can reduce plant growth, root penetration into the soil and root size. Soil becomes compressed or 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 and 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% to 80% of compaction is done in the first pass. Compaction can vary depending on the soil type, soil moisture, tire size, air pressure levels and total loads. With conventional tillage, research has estimated that 90% of a field can be tracked on during the year. Some of this area can receive as many as four or five passes a year. By cutting down on the traffic in a field, compaction can be managed and the subsoil allowed to regenerate.


If possible, farming 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 when run on overly wet soil.


It is much better to work on dry or moist soil. Managing traffic patterns and using only portions of the field for traffic can help manage compaction by not driving on it.


A penetrometer can measure the force needed to insert a cone into the soil. This 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). Typically, 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 eight inches, depending on the type of soil.


Some other ways to reduce soil compaction include using only enough ballast to reduce slippage; running correct air pressures for the loads and reducing axle weight, as axle loads of greater than five tons increase subsoil compaction; and using radial tires instead of bias-ply tires. Radials can run at lower air pressure, which is directly correlated to soil compaction. The more air needed, the more compaction on the soil.


Harm-Hendrik Lange, customer solutions engineer, Continental Commercial Specialty Tires: 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. Higher humidity works a little like glue when creating a paper mache’ mold. Climates with high humidity (are like applying) paste to the clay paper strips, that once dry, creates a hardened and compacted structure. In field applications, surface tension between the dried clay particles prevents the soil from being released easily with implements.


In addition, the first passage with 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, 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.


Soil assist sensor systems (SASS) can be placed in the soil to measure the deformation from tire pressure and deflection. Normal soil penetrometers can give a first feeling, while measuring the compaction of untouched and under-tracked soil, in comparison to the same soil and on the same day. But with the penetrometer it’s difficult to really repeat comparable numbers on different days or to compare values measured on different fields and with different humidity levels.


Furthermore, if small stones are in the soil, this can disturb the values and precision of a penetrometer a lot. Compared to SASS, the penetrometer is rather a rough indicator to give the end user a feeling of how he/she is harming the soil. But unfortunately, it’s less repeatable. 


Greg Gilland, vice president, global agriculture, Maxam Tire North America: In agricultural operations, the primary driver of 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, this 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.


Soils will vary around the world, but they are essentially made up of the following materials in various amounts: clay, silt, sand, organic material and water.  e amount or content of the various components listed above will determine the soil porosity of the field. Understanding the type of soil and moisture conditions a farmer or grower is facing will help optimize his equipment utilization and selection of air pressure to carry the load, with the intent to minimize soil compaction and improve his yields. 


Soil compaction is impacted by the following: initial soil pore volume (porosity of the soil / mix of soil); perceived or measured water content in the soil; vehicle speed or compaction speed when operating equipment in the field; the amount of ground pressure, consisting of tire footprint and air pressure caused by axle load; and the effect of multiple passes on the same area or rows by equipment.


Ground pressure is therefore directly impacted by the tires working the field based on the below contributing factors: total vehicle load per axle and number of tires; the distribution of the load on each individual, dualed or tripled wheel position; the type of tire construction — radial or bias — with the tires’ corresponding ground pressure; tire inflation pressure per the vehicle or towed weight; the tire’s gross flat plate or contact surface area due to tread dimension and lug design; the amount of power applied and subsequent ground slippage; and the type and weight of the selected implement in operation.


Surface soil compaction is mainly impacted by tire footprint pressures. 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 by the type of soil and moisture content.


A widely accepted solution to the problem of soil compaction is the implementation of controlled 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. A traffic path plan will improve vehicle performance, limit the impact to soil conditions and improve productivity by avoiding row or traffic overlapping.


Overlapping the row or traffic lanes results in wasted energy, escalating fuel costs and increased soil damage due to the subsequent ground pressure generated with every pass. The use of new, GPS-driven controlled path technology is revolutionizing equipment operation by improving vehicle utilization and reducing the impact of soil compaction on crop yield.


Keep in mind that the selected equipment will pass over the same field multiple times to deliver seed, nitrogen, fertilizers, nutrient and pesticides during the growing cycle. From Maxam’s perspective, if the right tire is utilized and the vehicle actively employs guidance technology or employs a traffic plan, the farmer or grower will avoid row skips or overlaps, ensuring reduced soil damage and improving crop yields. 


David Graden, operational market manager, agriculture, Michelin North America Inc.: 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., and that’s where I begin to see a few ‘a-ha’ faces in the audience. Finally, I give the answer, which is ‘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. This is a layer of soil that is impermeable to water and oxygen, thus hindering the development of yield. In fact, if soil has a higher moisture content, soil compaction damage will be 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. Additionally, taking the grain load process off the field has a major impact on field ends as high-pressure tires with exceedingly high weights — coupled with existing multiple tire track soil compaction — can easily result in a difficult- to-remedy hard pan.


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


Yet another idea is to outfit end users’ machines with very-high flexion (VF) tires. Independent studies at Harper Adams University in the United Kingdom and the University of Illinois have proven a yield gain of up to 4.31% using properly inflated Michelin VF tires versus standard radial tires. This means improved efficiency, higher yields and a much faster return on investment.


Finally, if your customer thinks that soil compaction has or is hindering the root development of his crop or is negatively affecting yield, you could use a cone penetrometer. This tool is used to measure and record the downward force required to penetrate Soil compaction is a very big issue and it is di cult to measure its e effects, year-over-year, in normal farming operations. On the other hand, most of us completely understand that oxygen, water and nutrients are necessary for healthy root development and compacted soil restricts all of these. At Michelin, we continue to focus on the development of technologies that improve yield and efficiency by reducing soil compaction. 


Blaine Cox, Yokohama Off-Highway Tires America Inc.: Soil compaction can have a huge impact on crop yields, soil health and water infiltration and it’s something you can help your customers minimize through careful tire selection and maintaining 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 tire that’s running at 25 psi. 


Compaction isn’t just isolated to the ruts left by tractors during planting. 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. 


We talk with farmers about the importance of selecting low-pressure options for as much machinery as possible. 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 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 tires last longer, too.


We would love to see more use of penetrometers to get to know what’s happening beneath the surface — as far as the severity and depth of soil compaction — but we know that’s also rare. But at the very least, we encourage dealers to dissuade farmers from 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. 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.


There are some other things you can do to help your customers manage compaction. In many parts of the world, farmers drive in the same tracks with all their equipment when they can — pass after pass, year after year. Those lines are high-compaction sacrifice areas and they allow farmers to keep o the rest of the field surface. 


Another thing you can do is look at yield maps and see if you can spot — or help your customers spot — tire tracks or other compaction damage. And take a look when cultivating or spraying this summer and see what’s stunted or yellow. You may see first-hand the effects of soil compaction. The good news is that tires can help minimize that in the future

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