By Douglas B. Gucker, Univesity of Illinois
Have you noticed that your field is not draining as fast as it did a decade ago? Do your yields vary greatly between a "dry" year and a "normal" one? Have you checked your soil for deep soil compaction or subsoil compaction? Compaction that is deeper than 8 inches.
The use of heavier equipment, multiple field operations, operating in less than ideal conditions due to time constrictions, and the consolidation of crops used in a rotation, all provide elements for "more extensive and deeper compaction" according to research out of the University of Nebraska.
Over the past 4 years, I have had the opportunity to view several soil pits in local fields. The disturbing fact is that most of these pits have a compacted layer below 12 inches deep in the soil.
Deep or subsoil compaction is caused by total axle load of the equipment. For example, a 12-row combine fully loaded as an axle weight of about 26 tons. Research shows that loads of these magnitudes will the soil to compact down to a depth of 24 inches. A loaded 1200-bushel grain cart will have an axle load of 35 to 40 tons, which will cause the soil to compact to a depth of 36 inches or more.
How do you get rid of compaction? The "freeze-thaw" cycle is helpful for compaction down to about 4 inches. A ripper implement used in dry subsoil can relieve compaction below 10 inches deep. The ripper needs to be operated 1-2 inches deeper than the compacted layer in dry soil to shatter the layer. If the ripper is operated in moist subsoil, it will actually add compaction down to that depth.
Make sure your implement is operating at the depth you think it is. Research out of the University of Minnesota has shown that a disc-ripper implement actually operates about 2 inches shallower than it is set. This appears to be due to the fact that the disc gangs throw soil causing the implement to ride higher.
Another way to attack deep soil compaction is through the continued use of cover crops. Research is showing that cover crops used repeated on the same field, year after year, create root channels through the compacted soil zones that subsequent crops can follow.
Confining field traffic to travel zones keeps the deep compaction restricted to travel lanes and not the whole field. University of Nebraska research has shown that in the course of a year, if random field traffic patterns are used for tillage, planting and harvest operations then almost 90 percent of the field has been subjected to soil compaction.
The key to higher crop yields may be as simple as checking your soil for compacted layers. Digging a hole 18 inches deep (and big enough a 5-gallon bucket can fit in it) will give you the opportunity to explore whether your field has subsoil compaction.
The photo shows a site where I found a compacted layer that extended 4-12 inches deep. There were literally no corn roots below about 5 inches.