Soil types vary from region to region, and although so-called dirt might seem the same from one place to another, it’s functional attributes—the components that make it soil—are what sustain a diverse types of life. Simply put: dirt is not simply dirt. Arizona soil, for instance, has three unique factors.
Arizona soils are rich in clay deposits. Clay consists of high phyllosilicate mineral deposits within the soil. When it comes to soil, clay is not the best thing to have. The reason is that these mineral deposits create a heavy, dense material that binds with nearly every material imaginable: hands, feet, shovels. Working in it is nearly impossible.
Although damp clay seems muddy and easily penetrable, what is happening is objects bind to the clay, and the clay slips against itself. The effect is a strangely difficult to dig yet extremely slippery, squishy substance.
In Arizona, however, clay actually helps more than it hinders. In dry climates, for instance, clay stores water along with many nutrients. In times of drought–think Arizona deserts–water and nutrients become precious resources. Arizona plants have evolved to take advantage of this, so a beneficial relationship exists between this specific type of soil and the landscape around it.
Another aspect of Arizona soil is a common sight. Because iron is not absorbed by clay, much of the flora in these clay-rich regions are iron-deficient, resulting in foliage permeated with a yellow hue.
Vast cave systems line Arizona’s undergrounds, calcium carbonate being one of the minerals that contribute to cave formations. In soil, calcium carbonate contributes to the creation of a dense, cement-like soil common throughout the entire state. This type of soil is called caliche.
It is created as carbonate minerals are drawn from the soil, leaving calcium carbonate behind to accumulate, thicken, and spread. It is also created by plants that absorb water and leave behind calcium carbonate. Both processes occur quick enough that caliche can develop fast enough to block drainages.
The caliche substrate can range in thickness of a few inches to up to six feet, making building difficult with anything but heavy machinery. Unlike clay, caliche cannot absorb water, and it is so dense that water cannot move through it. Additionally, floral roots cannot take hold within it. However, like clay, it can inhibit iron absorption in plants.
The one positive aspect about caliche is that although it makes farming difficult, it is so dense that it can be mined and used in a variety of building and landscaping projects.
Arizona soils are heavily infused with salt minerals. The department of agriculture estimates that nearly 275,000 acres are heavily infused with salt minerals. When salt is combined with clay, it gives rise to the most predominant soil in Arizona, Casa Grande soil.
The science behind Casa Grande soil
Casa Grande soil displays at 700 to 2,000 feet above sea level and is distributed across two types of rock substrates: fan terraces and relict basin floors. Unlike caliche, it is a slow-forming soil and very old, resulting from a process called Alluviam. Alluviam involves the salt-clay mixture, along with silt, sand, and gravel, to be deposited via slow-moving water sources around just about any surface or formation.
Taxonomically, the most widespread type of soil in Arizona is known as a Natrargrid. Generally speaking, a Natrargrid is defined according to the soil makeup, the environment, and the amount of clay and salt within the soil. Specifically, a Natrargrid is a soil, heavy in salt and clay content distributed in extremely arid areas, e.g., deserts.
The layers of Casa Grande soil reveal sandy loam in the upper layer, or A horizon. This upper layer typically consists of no more than one or two inches of sandy soil. Beneath the A horizon is the B horizon, a layer consisting of a thick clay. This clay is high in alkaline levels, which can reach as high as 9.6 pH.
Interesting factoids about Casa Grande soil
Ability to boil (well, sort of)
One interesting tidbit is that the alkaline levels in Casa Grande soil are so high that when someone pours vinegar on it, the surface will bubble as if in a boil.
A cautionary tale
Generally, the value of Casa Grande soil is educational. Specifically, the educational component is one of caution. Named after the Casa Grande region in which it was discovered, this type of soil results after heavy irrigation. Water is removed, and the salts are left behind.
When the Hohokam natives originally irrigated their crops, over 1,000 years ago, they were eventually left with the soil now known as Casa Grande soil. As the salts became more infused within the soil, the tribes were left with the inability to farm and survive. Eventually, they had to migrate out of their home regions in search of more hospitable, less-alkaline laden soils.
As a soil–nearly worthless
Soil scientists refer to Casa Grande soil as a “limited soil” in that it cannot be readily used for one or more of soil-related defined functions. The more things a soil cannot be used for, the more limitations it is said to have. Casa Grande is listed as a soil with multiple limitations.