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Roger Weller, geology instructor

by Michael Polombo
Physical Geology
Spring 2016
                                                                                 Everyday Soil: Geology and the Gardener


In everyday life we seldom give thought to the dirt beneath our feet, yet it is what we live on and prosper from.  From crops to construction, beach vacations to burial plots, soil serves an invaluable utility for mankind.  But it is a substance born of the natural world, and the study thereof is called pedology.  Soil is the part of the regolith down to the deepest penetration of plant roots.  There are around 14,000 types of soils on Earth giving home to vast biodiversity of Flora (Renton, 2015).





less than 10” annual precipitation







excellent for agriculture






Tropical--Hot and Wet  


100”+ annual precipitation

Climate shapes the soil (Renton, 2015)

The arctic and desert regions are places where organisms compete almost entirely against the elements (Darwin, 1859). In Southeast Arizona it can be a bear to keep up a garden; just try putting a shovel to the stubborn hardpan of our high desert terrain, or spending a full summer’s day outside without sunscreen!  Then one can experience firsthand the challenges our native plants endure.  Human help as a geological agent can ensure other species thrive. This is the role of the gardener:

 “…we may see clearly in the prodigious number of plants in our gardens which can perfectly well endure our climate, but which never become naturalised, for they cannot compete with our native plants, nor resist destruction by our native animals.” (Darwin, 1859)


Humans have been able to manipulate the environment in many ways---during months of harsh snow, greenhouses or atriums provide climate control for less hardy plants; utilizing these structures will be a fundamental part of colonizing other planets in the Cosmos.  Irrigation is artificial rain, and is commonly used to deliver moisture directly to plants.  Fencing material can be used to cage out grazing animals and pests.  Constructing good soil with compost or manure can boost agriculture yields. A “good” soil might consist of 25% air, 25% water, 45% mineral matter, 5% organic matter (Caffey, 2013).   Surface organic matter includes large woody material, duff and litter, and humus… is Mother Nature’s mulch, providing the underlying soil with nutrient reserves, and hydrologic function without erosion (Schmitt, 2011) For breaking up hardpan soil, include Chicory, Burnet and Vetch, and Lucerne into your cultivation area (Brunetti, 2013).



          All land creatures struggle with thirst, flora included. This inexpensive meter shows moisture, light, and pH readings.  The guide suggests 500-2000 lumens and a moisture level of six for Croton plants.  



Ecology of the soil is quite complex.  There are enough geologic nutriments in soil to feed generations upon generations of plants, though not all of it is readily accessible (Ingham, 2015).  Plant roots secrete acids so that exposed minerals are dissolved and made available to the plants.  Microbes aid in this mining operation (Vermeij, 2010).  Interestingly enough, microbes are half of the earth’s biomass, yet only a small fraction have been identified by science! (Brunetti, 2013).  Nevertheless, they do a lot of work within soils.  Protozoa eating bacteria release accessible nutriments in the root zone, so too when nematodes and micro-arthropods eat fungi (Ingham, 2015).  Additional nutrients from decaying flesh and leaves get absorbed back into the ground.

Soils are the foundation for much life on planet Earth.  (


A bottom-up collapse of the production means of the food web (plants) for an ecosystem can be caused by large objects colliding with Earth, or volcanic outbursts releasing dust and poisonous gas into the atmosphere (Vermeij, 2010).  Aside from such fearful disasters, sensible agriculture by humans will sustain our dinner plates without depleting the soil.  By fields which mimic natural prairies and forests--polyculture crops and year-round plant cover-- and realize the interconnectedness of organisms, undisturbed by tilling or dousing with artificial chemicals, can we continue the harmony of the earthen land (Archuleta, 2014). 




APA Bibliography

Archuleta, R. (2014) Soil Health Principles  {SARE outreach project}. Retrieved from:
Brunetti, J. (2013, June 30) Soil as a Supra-Organism.  {Landcare Education video}  Podcast retrieved from:
Caffey, J. (2013) Intro to OTC Geology—Chp. 6 Soil {videofile} Retrieved from:
Darwin, C. (1859) The Origin of Species by means of Natural Selection. London: Murray, Albemarle street.

Ingham, E. (2015, January 25) The Roots of your Profits {video file}. Retrieved from:
Renton, J. (2015, March 12). Soils and the Clay Minerals {Lecture 17} Podcast retrieved from:

Rice, J (2015, April 15) Report from soil biology school {Image}     Retrieved from:
Schmitt, G. (2011) Healthy Soils Build Healthy Ecosystems. {USDA Forest Service podcast}
Vermeij, G. The Evolutionary World (2010). New York: St. Martin’s Press.