Soil health goes to the microbes

Soil health is a hot topic nowadays, but what does it mean? According to soil scientist, Dr. Dena Marshall, “Soil health is emphasizing the overall diversity of soil biology, which then enhances the resiliency of the soil.”

Dena Marshall

Dr. Dena Marshall with soil monoliths — preserved soil samples of cover crop roots.

Soil health

Not only do soil microbes aid in the cycling of nutrients during decomposition of plant materials but they also secrete glomalins (a sugar/protein substance), which acts like a glue to bind soil particles together to improve soil structure and stability.

The million-dollar question is “how do we increase microbe numbers and diversity”? Dr. Dena Marshall has a few suggestions….

“Soil health is easily achieved using Never Till and planting Cover Crops to increase microbe biodiversity,” says Marshall.

Soil health & never till

“Research is finding Less is MORE!” says Marshall about the Never Till (or No-Till) practice. “The least amount of disturbance benefits the soil microbes most!”

The microbes that Marshall is referring to include: bacteria, fungi, protozoa, mites, nematodes and earthworms. All of these microbes contribute to building healthy soil.

“Both tillage and the non-judicious use of pesticides can harm these important organisms,” says Marshall.

“Tillage = habitat destruction! You know the wonderful smell of freshly turned earth? That’s actually the smell of billions of microbes dying…”

Microbes are the workhorses in the soil biology cycling system. Without them, the cycle is broken.

Soil health & cover crops

Cover crops not only provide a food source for microbes, but they also provide shelter and stability for microbes.

“It’s wildlife management on a microscopic level!” says Marshall.

Cover crops also:

  • Reduces pollution of our waterways because cover crops scavenge left over fertilizers.
  • Increases organic matter in the soil. OM increases available water-holding capacity in the soil. During drought, water-holding capacity is critical to planting success.
  • Decreases erosion.
  • Suppresses weed growth.
  • Provide valuable pollinator habitat (i.e. clover).


What cover crops can we use? USDA has a good list of cover crops. Dr. Marshall recommends a mixture of cover crops.

“A mixture of grasses and legumes is often best,” says Marshall because different cover crops scavenge different nutrients. “Grasses tend to prefer nitrogen and legumes and other broadleaves prefer phosphorus.”


Soil health with never-till & cover crops

“Various cover crops can be utilized to “till” the soil naturally,” says Marshall. “For example, tillage or daikon radish is useful for breaking up soil compaction.”

Annual or cereal rye also has deep roots that work well. Warm season grasses work well in long term situation.

Deep rooting cover plants open channels through compacted layers, which allows air and water to flow a little better through the soil.

Using never-till and cover crops eventually lead to soil that absorbs and retain water better (because of higher organic matter) as well as better air and water movement deeper into the soil. As compacted soil loosens up each year, the soil biology improves!

Final word

“Under intense management soil organic matter can be increased by 1% in as little as 5-10 years,” says Marshall.

As a gardener, 5-10 years seems like a long time. For a soil scientist, Dr. Dena Marshall, 5 to 10 years is “a microsecond in soil formation.



NRCS Soil Health website

The Real Gardener Blog: No-till tool for clay soil: daikon radishes

USDA list of Cover Crops

Wisconsin University State Extension. Using Cover Crops and Green Manures in the Home Vegetable Garden


Written by Cristina da Silva
Tuesday, May 27, 2014 in Plants & Soils

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