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News Release

Cover Crops Equal Real Benefits

Dan Gillespie



BATTLE CREEK, Sept. 17, 2014 - The topics of soil health and cover crops seem to be in every farm magazine you pick up these days. In every case, the featured farmer is talking about how he or she is improving the soils on his farm and also improving his or her crop yields. Let's take a look at a few of the main reasons why this is happening.


Physical soil improvements - The first step to soil improvement is to simply park the tillage equipment and let Mother Nature restore the soil to its original structure. Tillage implements work by forcing soil over sweeps or against blades to invert the soil. In the process, the required pressures destroy soil aggregates and decrease the pore space that the freeze-thaw events of the past winter have created.

The destruction of the pore space drastically inhibits the infiltration of rainfall or irrigation water. Limited pore space will not allow air to escape readily from the soil profile. Without this gas exchange capability the water cannot readily enter the soil profile.


Residue cover is key - Raindrop impact on the bare, tilled soils literally bombs the exposed soil aggregates into its smaller components: silts, sands and clays. The lighter silts and clays then float in liquid suspension to the small pore spaces and plug them. 

The protective crop residues no-tillage leaves on the soil surface deflect the energy of the raindrops and prevents the soil surface from becoming sealed. Step one is harvesting more of the free moisture received and storing it in the soil for crop use.


Lower soil temperatures - Soil surface temperature is a key factor in crop water use throughout the season. Evapotranspiration, or ET, is a combination of the soil water lost through leaf and soil surface evaporation and soil water transpired by the plant in the process of photosynthesis. Crop residue and cover crops provide surface shade and drastically lower the soil temperatures at the surface and further down below. 

Mid-day surface temperature readings under full sunshine comparisons will show residue-covered soils in the middle 70s to middle 80s, while bare sandy soils can read up to 140 degrees. Our soil livestock, which are the bacteria and microbes, like to be in the shade as much as we do on a hot summer day.


Here are some interesting soil temperature facts:

  • At 70 degrees soil temperature, 100 percent of the soil moisture is used for plant growth.
  • At 86 degrees, soil microbial activity begins to decline.
  • From 95 to 113 degrees, 15 percent of soil moisture is used for plant growth and 85 percent for ET.
  • At 113 degrees, soil bacteria start to die.
  • At 130 degrees, 100 percent of soil moisture is lost through ET.
  • At 140 degrees soil bacteria, the genesis of the soil biology, die.


Growing plants and living roots - So where do cover crops enter the picture? Mother Nature built our prairie soils to the pre-cropping era 4-7 percent organic matter range by capitalizing on every moment the soil temperature was able to support root growth, which can be up to nine months of the year.

In our Northeast Nebraska corn and soybean crop rotations, we have living roots actively growing in the soil profile for four to five months of the year. Cover crops extend this period of active soil biology and allow us to emulate Mother Nature's way of soil building. Her game plan is to always have plants photosynthesizing and roots growing.

The photosynthesizers are the first level of the soil food web. The plant sugars produced in photosynthesis are leaked out of the roots to be fed on by bacteria, protozoa, fungi and nematodes that also feed on each other. The waste - root residues and metabolites resulting from this interaction - become plant-available nutrients and the components of soil organic matter.

By introducing cover crops that have different rooting structures than corn and soybeans, producers can improve soil structure up to 3 feet or deeper into the soil profile. Improved soil structure means improved water infiltration and storage.  A 1 percent increase in soil organic matter can store an extra two-thirds of an inch of water in that foot of soil. 

Cover crops provide more soil surface cover in the spring and early summer when the cash crops have not yet reached canopy and are unable deflect raindrop energy and shade and cool the soil surface. Corn and soybean seedlings enjoy a cooler micro environment with less wind under a cover crop's protection. The cooler soil environment also supports fungi communities that are active in breaking down the previous year's crop residues.

The carbon dioxide released in the residue cycling is released into the plant canopy, making a carbon-rich environment that allows for the plant stomata to intake the needed carbon quicker. The reduced time the stomata are open makes for more efficient transpiration.

The biggest role cover crops may play in the future is in fixing nitrogen and sequestration of plant nutrients, primarily nitrogen and phosphorous. Any agricultural area where plant nutrients have the potential to leave fields through runoff and leaching through sandy soils or tiled cropland will likely see a push to alleviate those problems with the use of cover crops. 

As we so often observe, doing the things that emulate Mother Nature can solve or mitigate problems and, at the same time, improve profitability for farmers.