FERGUS FALLS, Minn. - Soil compaction can be costly in terms of crop yields, according to Jay Jabro, research soil scientist at the Northern Plains Agricultural Research Laboratory in Sydney, Mont.
Jabro spoke to over 200 farmers gathered at the Don and Dan Bradow farm west of Fergus Fall in west central Minnesota last month to learn about tires, traction and soil compaction and how those factors are interrelated. He claimed that in severe cases crop losses can be as high as 56 percent due to soil compaction.
Soil compaction occurs when the pore space is reduced between soil particles. Once that happens water movement through the soil is restricted, thus causing water runoff during periods of rainfall and the aeration in the soil is reduced. Compaction also inhibits the flow of nutrients in the soil, since that usually depends on water infiltration. All of these factors can contribute to stress on the plant, resulting in lower crop production.
Maximum soil compaction occurs when the soil moisture is at field capacity, which is defined as the moisture content of the soil after the excessive amount of water has drained away after the last storm.
"You don't go to the field when the moisture level is at soil capacity, since that's when maximum soil compaction occurs," Jabro said.
To reduce soil compaction farmers can do things such as deep tillage. He pointed out that Mother Nature also provides a way to reverse soil compaction through the freeze and thaw cycles that the soils in this region go through each year.
"This is the most effective and cheapest way to reduce soil compaction," he said. "So take advantage of the power of Mother Nature and use it."
Causes of soil compaction
Most growers would say that the travel of heavy farm equipment over the soil is the main cause of soil compaction; however Jabro pointed out that even various types of tillage operations can also cause a significant amount of soil compaction. Those tillage management systems that require few trips over the field certainly contribute less to the soil compaction problem.
Cropping systems can also relate to soil compaction. For instance a continuous small grain rotation may have a higher degree of soil compaction than a crop rotation that includes plants that have a deeper root system, such as sunflower, alfalfa or sugarbeets. These deeper root systems help to break up the soil.
Trampling over the soil by livestock, such as when they are grazing, can also lead to increased soil compaction.
Measuring soil compaction
Growers can use a device called a cone penetrometer to measure compaction in a field situation. Jabro demonstrated how this instrument is pushed slowly in the ground to measure soil compaction at the various depths as the probe goes lower in the soil profile.
The force needed to push the probe into the soil is measured in pounds per square inch (psi), and is displayed either on an analog dial or a digital display, depending on the model being used.
For those not wanting to spend several hundred dollars for a penetrometer, Jabro said a producer can use some type of small probe, or even a shovel to get some idea of how much effort it takes to penetrate the soil.
He noted that soil compaction tests are soil moisture dependent; soils that are exceptionally dry will prove to be more difficult to push a probe through, and if they are exceedingly moist the probe will show less resistance than if the soil was in a medium moisture condition.
Soil density can also be used as a measure of soil compaction. For instance, a normal clay-loam soil has a density of 1.35 grams per cubic centimeter (g/cc) but that soil when compacted will have a density of around 1.6 g/cc.
And compaction can also be determined by the rate that water moves through a soil from the surface; the slower the infiltration rate the more compact the soil condition.
Jabro said soil compaction is a problem not only in this region but around the world as millions of acres suffer from soil compaction. By lessening soil compaction growers will not only be increasing their bottom line, but progress will be made toward increasing global food production at a time when that is becoming increasingly important, he added.