Cover crops benefit soil health through microorganisms


Wheat and red clover roots ... Pictured above, wheat and red clover roots. Photo taken April 24, 2019. Submitted photo.

Nematode and bacteria ... A nematode and bacteria (the little dots) under magnification. Submitted photo.

Beneficial in so many ways ... Decaying turnip and worm castings (waste) provide a cyclical benefit to one another and the soil. Submitted photo.

Last fall was far from ideal for getting cover crops seeded.  The late crop harvest caused many producers to get cover crops planted very late, resulting in little or no fall growth. The few producers who planted cover crops following small grains or corn silage had the best opportunity for fall growth.

Depending on what was seeded, those cover crop fields may be carpets of green this spring.  One of the main soil health principles is to keep soil covered as much of the year as possible.

It makes sense that cover crops protect the soil surface from rainfall impact and erosion. But we don’t often think about what is going on below the surface. The cover crop roots help break up compaction but also provide food for soil microorganisms like bacteria and fungi. Because soil microorganisms are so small, we very rarely think about them; out of sight, out of mind. These miniscule organisms play very important roles in nutrient cycling.  Billions of microbes can be present in a teaspoon of healthy soil.

The best way to know what is going on beneath the surface is to get out and look at the soil with a shovel, use a penetrometer to test for compaction, and look at a sample under a microscope.  The Waukon NRCS office has a microscope and our Soil Conservationist, Alisha VanderWoude is very knowledgeable about identifying soil organisms. Most crop soils are bacterially dominated. Corn and soybeans thrive in soils with mixtures of fungi and bacteria. Fungi are incredibly important because they spread out through the soil and deliver nutrients and minerals to the plants. If you are interested in what’s living in your soil, take a small sample (around a tablespoon worth) from the top few inches, close to where plant roots are and bring it to the office for Alisha to look at with you.

In late April, we went to look at a few cover crop sites to see how the cover crops were growing. The first site was seeded to cereal rye last September following corn silage harvest.  The field looked like a carpet of green, 6-8” tall rye. Manure had been injected into it the previous week and injection lines were barely noticeable.  The penetrometer was used to test for compaction. We compared the reading in the tire tracks to the rest of the field and found no difference, indicating that the cover crop roots and aggregation are likely helping to protect against compaction.

A soil sample was mixed with water and a droplet was observed under the microscope. As expected, we found millions of bacteria, but were pleased to find a few beneficial fungi as well. While there can be harmful fungi in the soil leading farmers to apply fungicide, there are many more types of beneficial fungi that can keep the harmful fungi in check and provide many benefits for our crops, specifically playing a huge role in bringing nutrients to the crops.  The fungi also help create the glues that help the soil aggregate and hold together. Tillage destroys fungi, so the less disturbance, the better. Having living roots as much of the year as possible is especially important for the plants to provide food (sugars) for the microbes.

The second site had been seeded to a diverse mix of cover crops after wheat harvest at the end of July.  While most of what was seeded was winter-kill, there was a lot of volunteer wheat and red clover that was growing and armoring the soil. Decaying turnips covered the field and provided food for many beetles, worms and other insects.  There was a lot of diversity of critters visible to the naked eye.  When a sample of worm castings (poop) was observed under the microscope, many beneficial nematodes (little worm-like organisms) were present. These bacteria-eating nematodes release nutrients back to the plants.

If you have interest in having someone from the NRCS office bring a soil health bucket to look at some basic soil health principles in the field and look at a soil sample under the microscope, contact the office at 563-568-2246 ext. 3 or stop by 635 Ninth Street NW in Waukon.

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