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Soil Food Web Analysis Shows Biological Life & Balance

The soil is home to a host of creatures. Many, like earthworms and dung beetles, are clearly visible. Other species are much smaller – even microscopic. They run the gamut from bacteria and protozoa to mycorrhizal fungi.

“The biological life in the soil can perform its work most effectively when there’s a large population and when the species are in balance with each other,” says Jay Fuhrer, district conservationist with the Natural Resources Conservation Service, Bismarck, North Dakota.

Building soil

Building healthy soil is the work of the soil critters. Working in balanced unison, they cycle nutrients and build soil aggregates, thus, increasing water filtration. The result is healthy soil that withstands drought and heavy rains, and requires fewer purchased inputs.

If the balance in species is disturbed, beneficial services to soil health diminish.

“The soil fauna are like creatures in a jungle,” says Fuhrer. “For instance, when there are inadequate levels of protozoa (they’re like lions) but high levels of bacteria and fungi (they’re like wildebeests), you won’t have much nutrient cycling going on in the soil.”

A soil food web analysis is a test that appraises populations of soil biology and evaluates the extent to which species are present in balanced proportions. The test results can point the way to management changes that will build increasing populations of diverse soil life.

In recent years, Fuhrer has run biological soil analyses on several farms, using the testing services of Ward Laboratories in Kearney, Nebraska. Large and diverse populations of soil life are present on farms where crop rotations and cover crops are most diverse.

Soil life

After several years of testing for soil biology along with growing cover crops, McKenzie, North Dakota, farmer and rancher Jerry Doan has seen steady increases in soil life. Besides cover crops, his crop rotation includes corn, sunflowers, wheat, and alfalfa.

He grows cover crops annually on 15% of his farmland. These covers are season-long, multispecies crops, planted at least by mid-June and allowed to grow throughout the growing season. He grazes half the acres, leaving the balance of the cover crops to stand over winter. He no-till plants into the residue in spring.

The cover crops grow as tall as 6 feet and yield 5 to 6 tons per acre of forage. Soil food web analyses show high levels of soil biology after the season-long cover crops.

“When we grow cover crops that include as many as 12 species of plants, the soil biology doubles or even triples compared to the biology present after planting a less-diverse cover crop,” says Doan.

Nutrient availability

The spike in biological activity translates into greater soil fertility.

“After growing cover crops for two years on the same field, I planted it to sunflowers that yielded 2,200 pounds to the acre of flowers with 42.5% oil content,” says Doan. “That was on land that had trouble growing that kind of a crop before.”

Because a high level of biological activity in soil makes nutrients more available to growing plants, Doan was able to grow the bumper crop despite cutting back on N inputs by 25% from soil-test recommendations.

A number of commercial laboratories now do soil food web analyses.

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