When you hear him speak on soil, it’s not so much a lecture though he’s been a professor teaching for the University of Arizona for decades. Instead, you hear a passion about Arizona’s climate and soil that stands out. One U of A graduate calls Jeffrey Silvertooth, Ph.D., the “King of Soils.” Dr. Silvertooth was our guest on KTAR’s Rosie on the House this last Saturday highlighting not only Arizona’s climate but the state’s soil type.

According to Silvertooth, “The State Soil of Arizona is the Casa Grande sandy loam that is commonly found in alluvial areas [soils deposited by streams and rivers over centuries] of Pinal, Pima, and Maricopa counties.”

He adds that Arizona soils are geologically young, fertile, and extremely productive if they are reclaimed and managed from excessive salt and sodium, which is a natural part of desert soils, and sufficient water is provided by irrigation.

As always, the “Farm Fresh” hour went fast but was a wealth of information worthy of an entire listen on one of your walks of jogs. We concluded this segment was also a celebration of one of Arizona’s Five C’s, climate.

The entire segment is embedded below, commercial-free.


Fascinating Facts about Soil

  • There is a common saying: “We owe our existence to a six-inch layer of topsoil and the fact it rains.”
  • Soil is considered the “skin of the earth.” Forming the surface of land, soils are complex mixtures of minerals, water, air, organic matter, and organisms that are the decaying remains of once-living things.
  • The main particles that make up soil are categorized into three groups by size: sand, silt, and clay.
  • Soils consist of vertical layers referred to as “horizons” that consist of humus or organic matter, topsoil, eluviated (transported) materials into lower horizons, subsoil horizons, parent material, and bedrock.
  • A quarter of a tablespoon of soil, or one gram, can host up to 10 billion bacterial organisms consisting of approximately 10,000 different species. This same amount of soil contains at least one million actinomycetes organisms and one million fungal organisms.  Soil is literally alive!
  • Only about 1% of the microorganism species found in soil have been identified.
  • Soil is one of the largest reservoirs of microbial diversity on earth; this includes many single-celled organisms, such as bacteria and archaea, as well as certain fungi.
  • 95% of food production relies on the soil.
  • Soils store more carbon than the atmosphere, and all the world’s plants and forests combined.
  • Earthworms are heroes of soil for aeration and more.
  • Soil serves as a medium for the growth of plant life.
  • Soil modifies the atmosphere by emitting and absorbing gases (carbon dioxide, methane, water vapor, and the like) and dust.
  • Soil absorbs, holds, releases, alters, and purifies most of the water in underground systems.
  • Soil is a living filter to clean water before it moves into an aquifer.
  • The relative proportions of sand, silt, and clay form the soil texture.

Arizona’s Climate and Impact on Soil

  • Arizona has 300-plus days of sunshine allowing us to extend our growing season.
  • In Arizona, farmers plant and harvest every month of the year.
  • While the Arizona climate lets us grow year-round, our sun can burn up the soil’s organic matter making farmers’ efforts to incorporate organic matter more challenging but doable. 
  • Our higher temperatures are ideal for certain crops, for example, cotton, that gains much of its growth in the hottest months of an Arizona summer.
  • Due to Arizona’s mild winters, Yuma became the Winter Lettuce Bowl Capitol of the Nation.

Sources on Soil and Climate: The University of Arizona, Dr. Jeff Silvertooth of the University of Arizona, and The Soil Science Society of America and Arizona’s farmers and Ranches.