Strategies Reduce Compaction
By JEFF BURBRINK
Extension Educator Purdue Extension
GOSHEN — Compaction of soils is always a worry when we have rain during harvest. But we can experience compaction from manure spreaders, lime trucks and other equipment crisscrossing the fields.
We have learned a lot about soil compaction over the past 20 years. Researchers world-wide have discovered that compaction in the topsoil is related to ground contact pressure only, compaction in the upper part of the subsoil is related to ground contact pressure and axle load, and compaction in the lower subsoil is related to axle load only.
What losses occur with compaction? Axle loads of 10 to 12 tons reduced yields approximately 15 percent the first year, decreasing to three to five percent 10 years after the compaction. Research suggests that 10 percent of the yield loss in the first year is due to compaction in the topsoil and upper part of the subsoil. The effects of the topsoil and subsoil compaction disappear in five to 10 years, while the subsoil compaction can affect yields three to five percent for many years to come.
There are several key issues to avoid or reduce compaction. The first is axle load (the total load supported by one axle), the heavier the load, the deeper the compaction. Freezing/thawing and drying/wetting cycles do not remediate deep subsoil compaction.
Research has shown that 10 ton axle load almost always causes deep subsoil compaction under wet to moist field conditions. When conditions are dry, deep compaction is less likely, even under higher axle loads. Axle loads of five5 tons are not likely to create deep compaction, although they may create surface compaction.
So, the best strategies to reduce deep compaction are to reduce the load, increase the number of axles (which spread the weight out), and to avoid field traffic in wet conditions.
Reducing topsoil compaction is also important. Research has shown that reducing tire pressure to minimal allowable pressures, using flotation tires, and using tracks or duals to replace single tires can reduce compaction. Likewise, radial-ply tires are more compaction friendly than bias-ply tires. Larger diameter tires increase the length of the footprint, which also reduces compaction.
Another factor on topsoil compaction is the type of tractor used. One advantage of four wheel drive or front wheel assist tractors is that weight is more equally distributed. A typical 2- wheel-drive tractor has approximately 75-80 percent of its weight on the rear axle.
Remember, however, that a 4-wheel-drive tractor might have higher axle loads than the 2-wheel-drive tractor because of larger total vehicle weight, thus increasing the chance of subsoil compaction. Ballasting the tractor properly is a simple task that can dramatically redistribute axle load as well as improve tractor efficiency.
A final strategy to reduce compaction is to reduce the number of passes over a field and to concentrate repeated traffic in travel lanes so that remedial action like deep tillage can be used in limited areas. It has been shown that driving faster shortens the load time delivered to the soil, which decreases the chance of surface compaction. However, driving fast can also increase the risk of tipping the tractor or wagon.