By Gary Sliworsky
Ag rep, Emo
Compaction is defined as increased bulk density and reduction in soil pore space.
This occurs when the soil particles are forced closer together by the impact of equipment, animals, and raindrops.
The use of heavier tractors, combines, and implements, particularly with earlier spring tillage, can cause problems under any tillage system.
Soils having high organic matter contents, good internal drainage, and good structure are less susceptible to compaction.
Soil compaction can be detected easily with inexpensive tools.
First, identify the areas that have potential compaction problems. Then using a tile probe or flexible rod, probe the affected area to a depth of 50 cm (20”) and compare to a fencerow or unaffected area.
Insert the probe into the ground at a slow steady speed. Your arms should be slightly bent, acting as the pressure gauge—measuring the force required to push the tip of the probe through the soil.
Note the depths at which the tip of the probe requires more force to push it through the ground. These areas may be where roots cannot penetrate.
Use a shovel to dig up the plants in the affected area and examine the roots. Compare the roots to healthy plants from an unaffected area.
The compacted area will have plants with malformed/restricted roots. Roots may be concentrated in the top few inches of the soil.
(Note: when using a probe to compare compaction in different parts of fields, the areas measured must have similar moisture content for the results to be comparable).
Meanwhile, there are a number of management options to help prevent soil compaction.
Ensure tillage operations are performed when the soil is at proper moisture conditions at tillage depth.
Use longer crop rotations that include forages/cereals, and leave forage crops in for more than one year.
Alternate tillage depth so that tillage pans are not created.
Minimize the amount of traffic on a field. Use radials, large tires, or tracks that create a long, narrow footprint to restrict compaction.
Reduce the tire pressure to reduce the force on the surface of the soil. But note this only will be effective with radial tires and with large enough tires to carry the equipment at the reduced pressures.
Check with the manufacturer that the tires are rated to operate at low pressures.
Avoid high axle loading, which will cause compaction in the subsoil—even with low tire pressure. Keep equipment weight and loads as low as practical (below 4.5 tonnes/axle or five tons/axle).
As often as possible, limit traffic with heavy equipment to laneways rather than tracking the entire field.
Subsoiling often is used to try to loosen compacted areas of fields where heavy loads have passed. Harvest of some crops results in severely compacted areas that require this measure.
Generally, though, subsoiling does not have a long-term effect. Always check for the presence of compaction using a tile probe or soil pit, and check the moisture at depth before subsoiling.
Deep tillage where the soil is not compacted will not provide any benefit and may damage soil structure below the normal depth of tillage.
Soil management, harvesting, and manure application practices must change to avoid further problems.
These changes include using lighter loads and staying off the soil when it is wet below the surface.