September 7, 2020
Think about crop residue and cover crops protecting the soil surface as soil armor. Just what is armor? Let’s go to the source!
From the Merriam-Webster dictionary, “armor” is defined as: 1) a defensive covering for the body; especially: covering, as of metal, used in combat; 2) a quality or circumstance that affords protection, and/or; 3) a protective outer layer, as of a ship, plant or animal, or a cable.
If you walked up to the average person and asked them what armor is, they probably would give some version of the first definition: a covering of metal or some more modern material used to protect the human body. In soil health circles, the word is used as it applies to the soil. All three definitions are appropriate when talking about armor in the context of soil.
Soil health applications
The definition calling armor a defensive covering is most common and obvious. The soil is very susceptible to erosion, both by water and wind, when left unarmed. How does one arm the soil? By keeping it covered 365 days a year with cash and cover crop residue, and by growing a cover crop through winter when heavy, intense rains cause severe erosion.
Having residue act as a shield against heavy raindrops and allowing growing roots to hold soil together is armor as a defensive covering. This defensive covering is physical — something you can see and know is valuable and important.
Armor as a quality or circumstance is a bit more ambiguous. How does this apply to no-till, cover crops and soil health? Soil armored by crop and cover crop residue is protected from the sun, providing two benefits.
The most obvious is slowing down evaporation from the soil surface and holding moisture in the soil so your crop can take advantage of it during periods of dry weather. What is a half-inch of moisture worth at the right time during a dry stretch of summer? Old-timers call them “million-dollar rains.”
Soil temperature is also impacted greatly by armor. The biology in the soil normally likes a constant warm temperature, not exceeding 100 degrees F. Many unarmored soil temperatures can reach 125 degrees or more, driving biology deeper in the soil or into dormancy. That biology is what converts nitrogen in the soil into a usable form for your crop. No conversion equals crop stress, which equals lost yield and lost profit.
As a protective outer layer, the third definition, armor on the soil provides a food supply for macrobiology and microbiology in the soil. Residue on the surface is the sole food source for earthworms, which break down residue and start the process of feeding millions of tiny organisms in the soil. These tiny organisms turn residue into usable and available nutrients for your cash crop.
Lack of surface residue correlates to a greatly reduced number of earthworms in the soil, which leads to less available nutrients for your crop. Less available nutrients from the soil means you need more commercial fertilizer. That eats into profit.
Donovan is a district conservationist with the Natural Resources Conservation Service. He writes on behalf of the Indiana Conservation Partnership.
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