What Lies Beneath The Soil

This week NRCS State Agronomist Gordon Mikell dug a soil pit in Dillon as part of a cover crop field day at Carl Coleman’s farm.  Gordon’s aim was to create a visual for those in attendance to see what lies beneath the soil surface.  We rarely get a look at, or even think about what is happening below the top 6 inches of the soil profile.


Gordon Mikell, NRCS State Agronomist

Traditionally we’ve only studied the top 6 inches since that’s where the majority of the plant roots are, but that doesn’t necessarily mean there’s nothing going on below that.  There can be significant amounts of nutrients down deeper in the profile as a result of leeching; however, yearly cultivation destroys soil structure and can create a hard pan that is difficult for roots to penetrate.  In an effort to rebuild the soil structure and alleviate the hard pan, a number of growers have switched to no-till systems and are experimenting with cover crops.


Cover crop of oats, vetch, and clover.

The field where the pit was dug (pictured above) hasn’t seen any form of cultivation in 4 years.  It has been in continuous cash crop and cover crop rotation.  The once existent hard pan is now gone and there is good structure in the topsoil.  In the photo below, you can see Gordon pointing to a root that has managed to grow down about 4 feet since there was no hard layer restricting it.  There were many others down there with it.


Roots visible 4 feet down.

Water infiltration is another concern that no-till/cover crop growers are looking to improve.  All of us have seen fields where pools of water collect after a significant rain event, especially this past fall.  In a soil with good structure, small channels exist that allow more excess water to drain through the profile rather than pool on the surface.  No-till/cover crop systems seem to be doing a good job of allowing the soil structure to rebuild in fields that had been cultivated regularly.  As a result, we are seeing better infiltration and much less water pooling in these fields.  Below is another pit Gordon dug just a few feet away from the first.  Using pond dye to make the infiltration visible, he simulated a 3″ rain event on the left and a 1″ rain event on the right.


3″ on left, 1″ on right

As to be expected in a heavy soil, the 3″ rain event spread  out more, but the water still penetrated several inches into the clay layer.  That’s impressive considering this field had a bad water holding problem several years ago.

Interest in cover crops has taken off in recent years.  Growers are seeing benefits in weed suppression, nutrient cycling, maintaining organic matter, infiltration, increased biodiversity, etc.  For more info on cover crop systems, you can contact your local Clemson Extension Agent or the NRCS.

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2 Responses to What Lies Beneath The Soil

  1. Carl Coleman says:

    Awesome job Justin. Thanks for all you do.


  2. Pingback: Pigweed Worse in No-till or Conventional? | Pee Dee Ag News

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