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Green Up Compaction

Putting in place a biological fix for soil compaction may take time, but the results could be worth it. “Poor soil structure is a biological problem resulting from a lack of living roots in the soil,” says James Hoorman, Ohio State University Extension educator.

The lack of living roots most often comes from excessive tillage and is associated with low levels of soil organic matter and soil compaction. This results in soils made up mainly of microaggregates that compact easily under the weight of heavy machinery. Hard rains also contribute to soil compaction when organic matter is low.

“A reduction in soil pore space greatly reduces water infiltration,” says Hoorman. “This leads to problems with standing water and soil erosion, and it results in increased surface runoff. Denitrification increases as soils become saturated with water due to a lack of oxygen.

“Plants growing in compacted soil are shallow-rooted and tend to lodge,” he says. “Shallow-rooted plants have difficulty surviving any type of extreme weather, such as drought, wind, or excessive moisture. Crop yields can decrease by as much as 30%.”

Putting in place a biological fix may take two to three years to achieve improvements in soil structure and reductions in compaction. When the biological solutions are continued, soil restoration is more permanent, while mechanical solutions are short-lived.

Hoorman suggests these four steps to biologically improve soil structure to reverse compaction and to restore soil porosity.

1 Reduce tillage. 

“Tillage destroys soil structure,” says Hoorman. “It also disrupts the microbial population and tends to promote bacteria populations over fungus. Mycorrhizal fungi are important because they help make glomalin, the glues along with other microbial wastes and root exudates that form the macroaggregates. These give soil porosity and are a major storehouse for soil carbon and soil nutrients.”

2 Grow cover crops. 

Planting cover crops annually after every crop keeps living roots in the soil and maximizes the building of organic matter. 

“Keeping soil covered with live plants promotes good soil structure, because there are live roots in the ground year-round,” says Hoorman. “This supports a microbial population that has a healthy balance of bacteria and fungi.”

3 Plant diverse species.

Including diverse species in each planting ensures a wide range of food sources for microbial life. This promotes a healthy balance of bacteria and fungi populations. Diverse species differ in root structure. Each structural type performs a unique service in the soil profile.

“Plant a mixture of legumes, grasses, and brassicas in the cover crops,” says Hoorman. “Grass roots tend to be fibrous and supply carbon and phosphorus. Legume roots tend to have a deeper taproot and supply nitrogen to balance the ratio of carbon to nitrogen. Brassicas tend to reduce weeds and greatly promote beneficial microbial populations.”

4 Cover soil with residue. 

A thick layer of crop residue on the surface of the soil serves as a cushion, reducing the soil-compacting weight of tractors and other field equipment.

“The residue is also important for reducing soil erosion,” says Hoorman. “It improves water infiltration, and it regulates oxygen and carbon levels in the soil. If you remove the residue, it’s like removing the roof on your house or barn.

“Mechanical solutions to soil compaction are short- lived, typically lasting only one year, and may actually contribute to soil compaction and poor soil structure in the long run,” he says. “Taking a biological approach to reducing compaction may be a slower process, but if continued, it is beneficial and long lasting.”

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James Hoorman

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