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The Life of Soil

Posted by Beth Allhands -

"... I cannot conceive of the time when knowledge of soils will be complete. Our expectation is that our successors will build on what has been done, as we are building on the work of our predecessors." - R.S. Smith, Director of the Illinois Soil Survey, 1928

R.S. Smith was right, there is still so much to learn about soil, and scientist are discovering new things all the time for this often over-looked substance. Soil is as essential as water, air and sunlight to sustain life, but what is it made of?

  • · Soil is a dynamic combination of minerals, water, gases, organic matter, macro-organisms and microorganisms.
  • · Minerals comprise the largest percent; about 45%-50%.
  • · Water and gases fill about 45% of the spaces between the mineral derived particles; the ratio of water to gas present at any one time depends on soil texture, precipitation, and other factors such as topography.
  • · Organic matter, which is decayed plant and animal tissue, makes up 1-5% of the soils.
  • · Microorganisms are the final basic building block of soil. They only contribute 1% or less to the volume of soil, yet they are super high in numbers.

Soil Microbiology and Soil Biosphere is the fastest growing research in soil science. Many symbiotic relationships of roots and microbes are known to affect nutrient uptake ability and in decomposing organic matter back to the original elemental building blocks for plant growth. Other functions include buffering water flow, filtering contaminants, carbon storage, biological control of harmful pathogens,antibiotic development and even new research into microbes that actually can work like serotonin to enhance mood.

A decade or less ago researchers were estimating that one thimble of soil may contain more than 20,000 microbial organisms. Today, researchers now estimate that there billions of microbes in that amount; in fact there are more microbes in one teaspoon of soil than there are people on earth. Besides the sheer number of microscopic life; different locals of even a few meters apart has widely different species of microbial life present, with an estimate of 10,000 to 50,000 species per gram of soil.

Each teaspoon is literally a gigantic microscopic world of nematodes, bacteria, actinomycetes, algae, fungi, protozoa's and other life forms; most of which is not yet understood.

Enough is known to understand that without this life, soil is essentially dead and would not even have the wherewithal to anchor roots in the ground.

While we are waiting for new discoveries of what's teeming underfoot, there are simple ways you can keep the soil healthy and support the wonderful diversity found in it.

  • Add organic matter to you soil. Things like mulch, compost, shredded leaves, and grass clippings are food for the trillion or so new friends we are just becoming acquainted with.
  • Reduce tilling the soil, when possible. Tilled soil releases carbon back into the atmosphere, and disrupts natural channels, patterns and networks underground.
  • Keep the ground covered. Mulch and cover crops reduce soil erosion.
  • Don't compact the soil by staying off of it when too wet. Compaction forces all the air out between soil particles, and roots, bacteria and all the other life forms underground need oxygen to live.

At the beginning of this article, I likened soil to a substance as important as air,water and sunlight in sustaining life. However, it behooves us to remember that soil is not comprised of inert particles of minerals, gas and water. Within that structure, it is actually a living blanket on earth's surface of far more diverse life than easily imagined, with more being discovered all the time.

Here is a romantic poem to celebrate the diverse richness of the often under-appreciated ground we walk on- that medium from which life sprouts.

"A rainbow of soil is under our feet; red as a barn and black as a peat. It's yellow as lemon and white as the snow; bluish gray. So many colors below. Hidden in darkness as thick as the night; The only rainbow that can form without light. Dig you a pit, or bore you a hole, you'll find enough colors to well rest your soil." - A Rainbow of Soil Words (by F.D. Hole, 1985)

For further reading, start here.

http://www.sare.org/Learning-Center/Books/Building-Soils-for-Better-Crops-3rd-Edition/Text-Version/The-Living-Soil/Soil-Microorganisms

http://articles.extension.org/pages/54401/basic-soil-components



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