It's raining as I write this. And last I checked, tile risers were froze, and the frost layer was still around 4 inches. There’s not a lot of places left for melting snow and rainfall to go. While, it’s a very positive thing that we are heading in to the growing season with adequate soil moisture, (the first time in 2 years!) it does add some additional challenges when thinking of the anhydrous left to apply, dry fertilizer to spread, and planting coming soon. I recently ran across an article in Pioneer’s Agronomy Sciences Research Summary that I thought was very applicable given our circumstances. The article was on machinery options for reducing soil compaction. With our current situation in mind, I did a little more research and want to share some summaries from several articles. Hopefully this knowledge will help you make more educated decisions as spring arrives.
The Effect of Compaction on Crop Production
We all know compaction is a reality of some years. We sometimes have to be in the field before soil conditions are ideal. Particularly, when we start targeting early planting dates as a way to increase yield, we more frequently run into situations where soil conditions are not ideal.
Over the last several decades, size of equipment has increased dramatically. While this also allows us to cover more acres in the same amount of time, we trade that increased efficiency off for an increased risk of soil compaction. This compaction not only reduces the plant roots ability to expand and provide water and nutrients to the plant, but also reduces the pore space of the plant resulting in less soil available water in the first place. Compaction can be long lasting and hard to pinpoint. Many times compaction may be the cause of some problems that we unknowingly attribute to other problems. Yields can be impacted by more than 15% in the initial year after compaction, and continue on for several years with a 3-5% impact on yield.
Types of Compaction
We can group compaction into two groups. Surface and subsurface compaction.
Surface compaction is the result of contact pressure. This is determined by the total axle load divided by the area your wheels are coming in contact with the soil surface. If we increase the surface area in contact with the soil, or decrease the tire pressure, we will reduce our contact pressure and reduce our compaction.
Subsurface compaction is due to axle load and is not determined by contact pressure. Axle load is defined by the total weight carried by an axle. Axles will not always carry the same load. A 4 wheel drive tractor will have a more even weight distribution than a combine will. Axle loads that exceed 10 tons are likely to cause compaction that extends to the subsoil. Loads less than 10 tons but greater than 5 tons will cause some surface compaction and upper subsoil compaction. Loads less than 5 tons will only cause surface compaction.
Influencing Factors
Control Traffic
The well-known adage that 80% of compaction occurs on the first pass is a true statement. It would be wise for producers to follow previous tracks as much as possible. Its important to remember that additional passes still do add to overall effects of compaction. It’s still much better to follow previous tracks as much as possible. Follow this principle particularly when hauling heavy loads through the field, such as grain carts at harvest, or slurry tankers or manure spreader. Additionally, adding an axle to these heavy loads can help reduce the surface compaction by decreasing the contact pressure.
Time
The time spent in one spot will also impact the amount of compaction. Interestingly, increasing your speed will reduce your compaction impact because you spend less time sitting in one place.
Options to Reduce Compaction
Tire Pressure
Reducing tire pressure will help decrease the contact pressure and reduce surface compaction. However, optimal pressure for field work is much lower than what is needed for road travel. New systems with on board compressors allow producers to change the pressure for road travel vs field work. Adding duals and triples to spread out the surface contact will also reduce potential compaction. Keep an eye on tire pressure as air temperature changes. Each air temperature change of 10 degrees can result in a 1 psi change in your tire pressure.
Tracks
Recently, the incidence of tracks on new tractors and combines as well as after market options has skyrocketed. One major benefit is the ability of tracks to spread out the contact pressure longitudinally rather than horizontally as duals would. While tracks are able to spread out the contact pressure, they still have zones of higher pressure under each axle.
A study from Ohio State found that the between tires and tracks, the best way to reduce compaction down to 20 inches was to run duals at a low tire pressure. In situations where a higher tire pressure is needed, such as spraying or planting, tracks resulted in lower compaction. Finally, with heavy axle loads, tracks were an advantage to tires for surface compaction, but the subsurface compaction would still be similar for both.
Reduce Total Axle Load
When possible, reduce total axle load by using a smaller tractor or implement for each operation. Calculate the required horsepower for each operation and try to use the tractor closest to those specs as possible to reduce unnecessary axle weight.
Looking to the Future
Are there any new inventions that will help reduce compaction? Or has the technology come as far as it can? One major change in agriculture moving forward might come with autonomous tractors. Common thinking suggests that we will move from one large tractor implement combo in the field to several smaller units operating as a fleet. This will reduce total axle load for each unit and result in less surface and subsurface compaction across the field. Another advantage is the ability to plan routes and keep units on a specific planned traffic path.
Optimal Field Conditions
Of course, one of the best ways to reduce field compaction is to wait for optimal field conditions. Particularly, restrict any tillage activities until field conditions are better in order to not cause long term damage to soil structure. As best as possible, wait for field conditions to improve before any springtime activities of fertilizer and planting. An easy way to check is to form some soil into a ball. Toss the ball of soil into the air. If it shatters upon contact, your soil conditions are likely okay for field work.
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