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 Dr. 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.
“Compacted soils impact root growth. Soil compaction falls in two categories, deep and shallow,” said Shearer. “Deep compaction can take 10 years to mitigate. It is found at a depth of 18-36 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.” Operating smaller equipment and operating in dryer soil conditions reduces the chance of causing compaction.
Shallow compaction is driven by contact points between the tires and soil. “We can cause compaction in seconds, but it takes decades to repair compaction damage,” said Matthias Settler, Ag. Engineer from Bern University of Applied Sciences in Sweden. Compact soils are more prone to rill and sheet erosion, and the wheel tracks stay wetter.
Pinch row compaction involves what is going on in the surface. “If you see the tire depressions in the soil from a planter, there will probably be a yield reduction,” said Shearer. “Planters on tracks are showing less compaction than planters with tires. There was yield advantage range of 2.2-10.4 bu/ac 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.
Contact between the soil and tires is where compaction occurs. This is due to a combination of the soil strength and also soil-tire interface pressure. “Dry soils equal high soil strength, and wet soils equal low soil strength,” said Shearer. “Soils with high soil organic matter (OM) have high soil elasticity. Conservation tillage allows for good soil structure and better water drainage.”
“As we reduce the tire pressure, we spread the tire over a greater area, and the contact area is greater,” said Shearer. “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.
goal is to have the soil contact pressure under 6psi. “Under those pressures, the impact on plant growth is substantially reduced,” said Shearer. “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.”
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,” said Shearer. “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.”
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.
It is important to remember that “Even tracks have pressure points with the idlers and driver. It is not one even contact point across the entire track,” said Shearer. “The weight transfer on the axles or pressure points also has an impact when pulling an implement.”
There are precision tillage technology advancements that all the major manufacturers are coming out with. “One example is the AFS Soil Command, which is a prescription tillage tool,” said Shearer. “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.”
“High speed tillage is not same as vertical tillage,” said Shearer. “There can be concerns over tillage pans caused by this practice. High speed planting, like the tillage, both these reduce the grow vehicle weight (GVW) and ballast weight of the tractor.”
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.