Reducing Soil Compaction with Roots and Cover Crops

By Andi Anderson

Soil compaction is a sign of poorly functioning soil, often caused by excessive equipment use, insufficient biological activity, and excess nutrients. Brian Dougherty, an Understanding Ag consultant, highlights how compaction can hinder plant growth by restricting root penetration, water movement, and gas exchange.

Well-aggregated soil, resembling black cottage cheese, has good pore space for air, water, and nutrients, while compacted soil becomes dense and unyielding.

For plants to thrive, roots need to penetrate the soil to access water and nutrients and ensure adequate gas exchange. This process relies on a natural cycle where roots exchange oxygen and carbon dioxide to break down food. However, reduced oxygen and carbon dioxide exchange, caused by compacted soil, limits plant growth and crop yields.

Roots, along with earthworms and other soil organisms, help maintain interconnected pore spaces that allow water, nutrients, and gases to flow freely through the soil. These interconnected spaces are vital for root growth, nutrient absorption, and water infiltration.

Roots also contribute to soil aggregation by releasing sugary exudates and supporting the growth of beneficial fungi that produce glomalin, a substance that helps bind soil particles together.

When aggregates are destroyed, it leads to excessive nutrient release and soil compaction. Without living roots, soil structure deteriorates, and compaction worsens. “No living roots, no glues, no aggregates!” Dougherty stresses.

Deep tillage is often seen as a solution, but it only offers short-term benefits. While it initially improves water infiltration, it eventually destroys soil aggregates, worsens compaction, and increases the risk of erosion. “Deep tillage only produces a yield gain about 25% of the time according to long-term university trials,” Dougherty notes.

Cover crops offer a sustainable solution by increasing root mass year-round and continuously forming soil aggregates. Over a span of 3 to 5 years, cover crops can heal compacted soils and improve water infiltration down to 36 inches. With good growing conditions, cover crops can break through up to 12 inches of compacted soil per year.

Dougherty advises farmers to reduce compaction by keeping equipment loads as light as possible, aiming for no more than 10 tons per axle load on well-aggregated soils. Keeping tire pressure low (around 10 psi) further reduces compaction.

University studies show that controlled traffic reduces fuel consumption by 25%, requires less horsepower, and reduces soil compaction.

Excess nutrients, particularly nitrogen, magnesium, and potassium, can also contribute to compaction. Ensuring balanced nutrient levels, particularly adequate calcium, is essential for maintaining soil aggregation and preventing excessive compaction.

Earthworms play a crucial role in soil health, requiring ample calcium and helping to till the top 6 inches of soil over time. Their slime and castings enrich the soil with nutrients and improve water infiltration by up to 70%.

Dougherty emphasizes the importance of using cover crops to increase live roots, improve soil structure, enhance water infiltration, and reduce soil compaction, ultimately promoting healthier soils and better crop yields.

Photo Credit: gettyimages-sasiistock