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What is Soil?

Properties

Soil can be defined as a natural body that occupies earth’s surface that supports many forms of life. It is the upper biologically, physically or chemically altered portion of the unconsolidated material above bedrock.

How does soil form? Soil is the result of climatic and biological factors on parent material over a long period of time. Rock and other sediments are eroded by things such as rain, wind, plant growth, rivers, solar energy, etc. As it ages it becomes discernibly different than its parent material because it is dynamic. Its components are constantly changing.

A sample of soil can be divided into 4 main components (Ward, 2016):

  • Mineral matter – 45-49%
  • Organic matter – 1-5% (in general the higher the OM the darker the soil)
  • 25% pore space filled with water
  • 25% pore space filled with air

The mineral matter – otherwise known as soil texture – is further divided into sand, silt, clay and sometimes gravel (figure 1). Anyone can roughly determine soil texture by performing a simple texture feel test (figure 2).

I would rather be tied to the soil as a serf…than be king of all these dead and destroyed.”

—Homer, Odyssey

 

“Man and man’s earth are unexhausted and undiscovered. Wake and listen! Verily, the earth shall yet be a source of recovery. Remain faithful to the earth, with the power of your virtue. Let your gift-giving love and your knowledge serve the meaning of the earth.”

—Friedrich Nietzche

Figure 1. Soil texture is defined by it material composition.

Figure 2. Soil texture feel test helps determine what kind of soil you have. See “Guide to Texture by Feel” on the USDA website.

Conservation

It should be noted that soil is not the same as dirt. Soil contains microorganisms, macro-organisms and other organic matter. Dirt, on the other hand, is basically dead soil. It is with utmost importance that we conserve our soils. By using conservation methods we can increase our organic matter, prevent erosion, increase water holding capacity, decrease operating/fertilizer costs, and, in some in cases, increase profits.

 

Here are some hard facts and why we need conservation efforts:

  • The world’s prime farmland is finite
  • There have been drastic draw-downs of groundwater reserves due to plowing marginal lands unsustainable for sustained cultivation and by over irrigating.
  • Cropland is shrinking as highly erodible lands are abandoned.
  • One-third or more of the world’s agricultural land is losing soil faster than it is being replenished. It takes from 200 to 1000 years to form one inch of soil (Brown 2008).
  • Topsoil loss has a direct negative impact on cropland productivity

 

Conservation efforts aid in turning dirt back into soil. So where does one begin, how do we fix the problem? We can implement cover crops. Cover crops help build the soil and feed the micro/macro-organisms. Cover cropping also moderates soil temperatures, which leads to less evaporation and higher plant productivity. We can also implement no-till/minimal tillage. Heavy or constant tillage can lead to compaction and poor water infiltration. Further, leaving residue on the field can “armor” the soil to prevent erosion. Residue also adds to the carbon stores in the soil, which is pertinent to plant growth.

 

Although you might think cover crops will use too much water that might have otherwise been used for your main crop, it is important to note that for every 1% increase in organic matter, soil can hold an additional 16,500 gallons of plat available water per acre of soil. It is also important to note that reducing the use of fertilizer is essential to sustainable agriculture. Heavy fertilizer can actually harm the soil by disrupting natural nutrient cycles and actually contributes to erosion. Some studies suggest that future per-acre yields, even with chemical inputs, will begin to drop permanently if trends aren’t reversed (Smil, 1991).

 

How healthy is your soil?

“…As a farmer, man himself became closely attached to the landscape, firmly rooted to the soil that supported him. At times the soil seemed bountiful and kindly and again stubborn and unfriendly, but it was always a challenge to man’s cunning.”

—Charles E. Kellogg

 

“Soil erosion is as old as agriculture. It began when the first heavy rain struck the first furrow turned by a crude implement of tillage in the hands or prehistoric man. It has been going on ever since, wherever man’s culture of the earth has bared the soil to rain and wind.”

—Hugh H. Bennett and W.C. Lowdermilk, circa 1930s

Figure 3. Relationship of how using conservation methods creates a positive feedback for increased OM and productivity.

Soil Testing

Where does your soil stand? What areas are lacking? West Greeley Conservation District (WGCD) can provide those answers. We do soil sampling for FREE. WGCD performs site visits and soil probing. Generally, we take 15-20 samples in each area of concern. Then the samples are sent to a laboratory that can perform readings on NPK, pH, Salinity, Organic Matter, CO2 Respiration, and many other parameters. They can give recommendations on what cover crop may be best for a specific situation as well.

 

Sampling is done in a grid or random pattern and samples are taken at 0-8 inches. The filed is divided into sampling units according to topography. For example, side-slopes are represented with one sample, low areas with another, hilltops with another and so on. Areas of a field that have had different crops, fertilization or liming should also be sampled separately. Sampling should occur when conditions are stable; climate, year, etc. Sample odd areas separately.

“To be a successful farmer one must first know the nature of the soil.”

—Xenophon, Oeconomicus, 400 B.C.

 

“If the soil is destroyed, then our liberty of action and choice are gone…”

—W.C. Lowdermilk, 1953

 

“Whoever could make two ears of corn or two blades of grass to grow upon a spot of ground where only one grew before, would deserve better of mankind, and do more essential service to his country than the whole race of politicians put together.”

—Jonathan Swift, Gulliver’ s Travels, 1726

Figure 4. Correct soil sampling. (A) Aerial photograph of a field (B) Zones partitioned based on characteristics and topography (C) Equal sized field grids (Rains and Thomas, 2001)

Brown, Lester (2008). Plan B 3.0: Mobilizing to Save Civilization. Earth Policy Institute. New York: W.W. Norton.

Nadakavukaren, Anne (2011). Our Global Environment: A Health Perspective. Waveland Press, Inc., 7th edition.

Rains, G.C. and D.L. Thomas. 2001. Soil-Sampling Issues for Precision Management of Crop Production. The University of Georgia, College of Agricultural and Environmental Sciences, Bulletin 1208.

Smil, Vaclav (1991). Population Growth and Nitrogen: An Exploration of a Critical Existential Link. Population and Development Review 17, no. 4.

USDA website (2016). Modified from S.J. Thien. 1979. A flow diagram for teaching texture by feel analysis. Journal of Agronomic Education. 8:54-55. Retrieved from http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/edu/?cid=nrcs142p2_054311

Ward, Raymond (2016). Ward Guide, Soil Properties. Ward Laboratories. Retrieved from http://www.wardlab.com/WardInfo/WardGuide

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