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2.1 Physical Characteristics
Restrictive Layers
Within a soil profile, one can encounter a
restrictive layer that impedes movement
of water and air or root growth. Restrictive
layers formed by vehicle and agricultural
machinery are further discussed with regard to
compaction (page 34).
In New Mexico restrictive layers are most
commonly bedrock, due to the shallow
nature of our soils, or caliche. Caliche is a
whitish soil layer of cemented carbonates
of calcium and magnesium, like chalk. It
is commonly formed in arid environments
due to high evaporation and/or plant water
demand. This high water demand removes
water from the soil and leaves behind
carbonates that act like cement, partially
restricting water, air, and root growth. Caliche
also affects soil chemistry, elevating the pH
and altering nutrient availability.
Components of a Soil
In the rest of Section 2.1, we will discuss the components of a soil (think of the boards, nails, and
paint that are the building materials of a house) and how they fit together and affect function (think
of how metal and wood combined make a door hinge, allowing the door to open and close). We
start with the mineral component, organic matter component, and air component because those
characteristics together affect the structure of a dry soil. We then address the soil water component
because a soil’s structure affects how water moves through it.