Digging into soil compaction

By Dusty Sonnenberg, CCA, Ohio Field Leader: a project of the Ohio Soybean Council and soybean checkoff

Soil compaction is a problem that almost every farm has, and no one likes to admit. Soil compaction is simply reduced porosity from a reduction of void spaces in the soil.

“Voids in the soil are caused by roots and by the seasonal freeze/thaw cycle,” said Scott Shearer, professor and Chair of the Department of Food, Agricultural and Biological Engineering at The Ohio State University. “Ideal soils have 50% void space. Half of the void space should hold water, and half should be air space. Compacted soils lack these voids. If we don’t have that mix, that is when we see a negative impact to crop yield.”

Soil compaction can be caused by adverse weather conditions and heavy equipment. Operating smaller equipment and operating in dryer soil conditions reduces the chance of causing compaction.

“Compacted soils impact root growth. Soil compaction falls in two categories, deep and shallow,” Shearer said. “Deep compaction can take 10 years to mitigate. It is found at a depth of 18 to 36 inches. Shallow compaction can be changed by shallow tillage. It can be easier to mitigate. The only way to prevent deep compaction is to not be in the field when it is too wet.

“Dry soils equal high soil strength, and wet soils equal low soil strength. Soils with high soil organic matter (OM) have high soil elasticity. Conservation tillage allows for good soil structure and better water drainage.”

Shallow compaction is driven by contact points between the tires and soil. Soils with surface compaction are more prone to rill and sheet erosion, and compacted wheel tracks stay wetter.

“If you see the tire depressions in the soil from a planter, there will probably be a yield reduction,” Shearer said. “Planters on tracks are showing less compaction than planters with tires. There was yield advantage range of 2.2 to 10.4 bushels per acre by alleviating pinch row compaction.”

There are some practical ways to manage practices and reduce compaction, such as controlled traffic, new tire technologies, and prescription tillage technology. Controlled traffic has been discussed for a number of years, and became more applicable with the adoption of RTK repeatable guidance technology, and matching equipment widths, to standardize equipment traffic patterns across the field.

Reducing tire pressure can also help minimize compaction.

“As we reduce the tire pressure, we spread the tire over a greater area, and the contact area is greater,” Shearer said. “This is an important take home message. Sometimes farmers need to let the air out. Farmers should target a tire pressure of 9 psi. They need to be sure to check the manufacture’s recommendations so they do not void the any warranty. Some tires require higher pressure to provide greater stability when traveling on the road.”

The goal is to have the soil contact pressure under 6 psi.

“Under those pressures, the impact on plant growth is substantially reduced,” Shearer said. “They should attempt to keep the axel loads under 5 tons per axle. The idea is to distribute the load on as many tires as possible. This may involve duals, or more axles.”

Central tire inflation systems (CTIS) allow an operator to change tire pressure on the go. Some newer equipment is already plumbed to facilitate these systems. Older equipment can be modified.

“Even tracks have pressure points with the idlers and driver. It is not one even contact point across the entire track,” Shearer said. “The weight transfer on the axles or pressure points also has an impact when pulling an implement.”

New equipment designs are spreading the weight of central fill planters out across the entire planter frame. There are other design options that allow wider equipment toolbars to flex across the terrain, reducing compaction and balancing the weight distribution. There are precision tillage technology advancements that all the major manufacturers are developing to help address soil compaction.

“One example is the AFS Soil Command, which is a prescription tillage tool,” Shearer said. “It uses GPS technology and mapping to manage residue. The map directs the tillage tool to adjust components independently. Maps are driven by grain yield and perceived residue amounts, as well as topography and farmer experience.”

Self-propelled sprayers can also cause soil compaction.

“The larger self-propelled sprayers with up to 2,000-gallon tanks and narrow tires with high psi can increase compaction,” Shearer said. “Lowering the tire pressure can help, and also switching to wider tires in the spring before row crop work helps. Wider tires at lower pressures mitigates some of the damage.”

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