Agricultural soils can become compacted by weather, tillage, traffic, or a combination thereof. When compaction (increasing the bulk density of the soil) occurs, root growth is restricted, water infiltration and water holding capacity is reduced, erosion increases and other detrimental efforts occur, all contributing to yield reduction. Unseen and undetected, soil compation steals yield like a thief in the night. At its worst, it can hack grain production by more that 40%.

Ideal soil tilth will contain 1-5% organic matter, 20-30% water, 20-30% air and 40-50% minerals. Anytime that water and air drop below 20%, yield will likely be affected. It allows for proper water uptake, air exchange and root growth. I believe we all except the fact today that what is above the ground is only as good as what is below the ground. Root structure is so critical.

There are good effects of some soil compaction. Moderate amounts of surface compaction contributes to good seed to soil contact, fast germination, and prevents excessive drying out around the seed.

How does soil compaction develop? Pressure, however it is applied to the soil, crushes soil aggregate which increases bulk density. This reduces pore space which results in a slower exchange of oxygen and carbon dioxide. It limits water nutrient movement and increases water content at the expense of air. Increasing bulk density slows root penetration and increases power requirements. These soil symptoms reduce water infiltration which in turn causes standing water, drainage problems and more surface erosion. When these soil symptoms are found the plant symptoms are going to be slow crop emergence, uneven stand, off color or purple leaf discoloration, shallow, constricted roots, malformed roots and moisture stress. Restricted roots lead to reduced uptake of both water and nutrients.

There are five critical words to remember when talking about compaction. It costs, it is created it can be detected, it can be cured and it must be avoided. We know it costs because there is a lot of research that has proven that fact. The champion corn grower, Francis Childs, has avoided compaction at all costs. He produced over 350 bushels of corn per acre on dry land farming. Compaction is created by weather, tillage (soil shear) and traffic. Traffic is affected by axle load, tire inflation, and track size. It is known 75% of compaction is caused on the first pass. The biggest culprits to compaction is heavy axle loads, loaded combines with grain tank extensions, grain carts, and honey wagons. If axle loads are heavy enough, compaction can be driven deep enough that weather or tillage will not be able to remove that compaction in our lifetimes. Because 75% of compaction is created on the first pass, controlled traffic can be a big advantage.

Once compaction has been created it then needs to be detected. Until this past year detection has been done with a hand held penetrometer. It was possible to collect data along with positioning, but a lot of work and very slow. CEE along with Midwest Independent Soil Samplers developed technology last year that detects how much and how bad compaction is in a field. We then convert the data into a computerized map. Using the same green-yellow-red scheme that is on a hand held penetrometer, the digitized maps paint compaction problems in living color. To create the maps we developed software that takes readings from a load cell mounted on a hydraulically powered penetrometer. We mounted the equipment on an ATV, pickup, and bean buggy. To generate the maps we drive the length of the field, taking a measurement every 100 feet. You then move over 100 to 200 feet and repeat the process. You normally would take at least two samples per acre. The software records compaction in 1" increments down to 24". That data is then averaged to show the average of the top 6" of soil and the average of the tillage layer from 7" to 10". The average from 11" to 18-24" is also mapped. We are still in the fact finding part of our research. But we have learned already that there is so much variability, you can’t make any generalizations about where compaction will likely occur. What happens with one soil may not happen anywhere else in North America. Last summer we mapped over 6,000 acres. In many cases, the best yielding soils are the most compactable. Farmers tend to think they don’t have compaction in those parts of the field, because that’s where their highest yields are. We also found that no tilled fields can have just as much compaction as fields that are tilled. You still have compaction caused by heavy axle loads, but you don’t have any tillage to break up the compaction in the top few inches of soil, but it doesn’t do anything for the compaction we have created in the tillage zone and below. It is more than just a compaction detector tool, the computer maps show farmers where they need deep tillage and how deep they need to run the shanks to take compaction out. It helps you make decisions about where to spend your time and diesel fuel. If you run deeper than you need to, it costs money and creates tillage sheer deeper in the soil. In the very near future you will be able to do an application map that will vary tillage depth automatically just as you are now doing with fertilizer, seed and chemicals. A compaction map is another layer of information. But it is an important piece in figuring out how to increase production with less inputs.

Curing compaction is never an easy thing to do. Freezing and thawing helps out with shallow compaction. But in the 7" to 10" zone freezing and thawing has only one pass at it and that is not enough to cure the compaction. In heavier clay soils the shrinking and swelling helps correct the problem. Tillage certainly is one answer as well as earthworms, tap root crops, manure, and zone tillage.

Compaction can be avoided by controlling traffic patterns. Attempting to keep your head lands as small as possible. Keeping heavy axle loads off fields as much as possible. Timeliness of tillage and planting is a very important factor.

In summary, compaction is created, detected, and corrected. Creating compaction is the easiest of these. But with the technology of compaction mapping now available, detection will become easier. Correcting compaction is the most difficult but with a good plan utilizing today’s tools, it certainly can be done.