Fort Collins Conservation District

Ron Neher

Soil compaction, - its presence unwanted!

By: Ron Neher, Natural Resources Conservation Service, Retired

It has once been said, “What you don’t see won’t hurt you.” Believe it if you wish but this cliché is far too present in our everyday life. Soil compaction on cropland is one of those things fairly invisible to the average eye. Many people do not know the tell-tale signs to look for in recognizing soil compaction on cultivated cropland. What goes on under the soil’s surface is commonly unnoticed by passersby and hence the effect of this menace goes undetected.

In the field of agriculture, soil compaction is far too evident on both irrigated and non-irrigated cropland. Many farmers, particularly on non-irrigated cropland, ignore it's presence as well as its effect on not only yields but also on conservation of the soil resource.

In order for plant roots to grow and mature, the roots need various soil conditions that are favorable for their development. One necessary item is pore space in the root zone. Adequate pore space between the individual soil particles and organic matter is necessary for soil aeration and proper water infiltration.

Soil compaction occurs in the soil as a layer of compacted and compressed soil. It can be identified by a hard compacted layer situated below the soil surface and can best be found using a shovel. As soil becomes compacted, the amount of pore space lessens due to the compaction. As this layer goes untreated, annual cultivation, planting, and harvesting continues to compress the soil particles together. The result is a somewhat impermeable (at least to some degree) layer of soil which hinders water percolation as well as root growth. Hence, precipitation and snow melt, as well as irrigation water, are hindered from infiltrating the soil. As roots are hindered in downward growth and development so is the yield of the crop. In addition, soil compaction increases runoff resulting in soil erosion, particularly sheet erosion, on cropland. The resulting sheet erosion can be quite dramatic on cropland which has a measurable slope.

Compaction on cultivated cropland is the result of the weight of various field machines, - tractors, implements, combines, and grain carts. The concentrated pressure created from tillage operations and wheel traffic, along with the weight of the equipment, has a dramatic effect on the underlying soil layer on the field. In turn, as equipment becomes larger and heavier, the result of compaction on the soil increases. Reducing field traffic through no-till farming is one option which can alleviate this problem. This is just another benefit of no-till farming which is causing this agronomic practice to grow in popularity.

Basically, soil compaction is one of those things which is unavoidable. It is going to happen as you drive farm equipment across your land for one reason or another. As the weight of the farm equipment is concentrated to the downward pressure of the tires, as well as the direct contact between the tillage equipment and the soil, the resultant effect of pounds per square inch (psi) compresses the soil particles together and decreases pore space in the soil.

An ultimate cure for soil compaction is to rip the soil when it is dry enough so it will cause a shattering effect. What type of ripper to use depends on the depth of the compacted layer as well as its severity. Many cultivated fields have never been sub-soiled or ripped and thus have a very hard layer.

Soil compaction has been known to exist in soils for over fifty years. It is commonly stated that annual freeze-thaw cycles over winter will take care of this problem. However, this is far from the truth. The freezing and thawing results on a compaction layer only has minimal effect in its removal.

So what is the remedy of this problem? Textbook examples tell us to cultivate only when it is dry so the moisture is not available to aid in compacting the soil. Following this example is almost impossible. Often times waiting on the weather and the prolonged time for the soil to dry out are literally out of the question. As a rule of thumb and generally speaking, using a ripper in late October is commonly thought to be an optimal time for this practice. This is usually when the soil is rather dry and will allow the soil to be opened up for winter moisture to infiltrate.