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Arizona Soils

The state of Arizona is characterized by great diversity in weather patterns. This diversity is readily experienced in a drive from Phoenix to Flagstaff. In November, you might start out the drive in shorts and sandals in Phoenix, where the daily high temperature can easily be in the 80-90 oF range. However, it wouldn't be that surprising to find snow in Flagstaff later that night!

Topography plays a role in the temperature change we experience between Phoenix and Flagstaff; ambient air temperatures decrease with increasing elevation at a rate of approximately 3 oF per 1000'. This phenomenon is described in greater detail in the Climate module of this website. The vegetation communities we observe on the trip from Phoenix to Flagstaff reflect the differences in both climate and elevation. The soils of Arizona can also be organized along these temperature and precipitation gradients.

One characteristic used to organize soils into classes is the amount of moisture available for plants to access over the course of a year. This characteristic is termed the soil moisture regime, and ranges from aquic, representing soils that are saturated year-round, to aridic, used to describe soils that are dry for at least half of the growing season.

Temperature is another feature used to describe soils. Soil temperature is measured at a depth of 50 cm. The soil temperature regime is a characterization based on three measurements:

  • Mean annual soil temperature
  • Mean summer temperature
  • Difference between mean summer and winter temperatures

Arizona can be readily split into four soil temperature zones:

Soil Temperature Zone

Mean Annual Soil Temperature at 50 cm

Hyperthermic

22 C (72F) or greater

Thermic

15 - 22 C (59 - 72 F)

Mesic

8 - 15 C (47 - 59 F)

Frigid

8 C (47 F) or less

 

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