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2.1 Physical Characteristics
How does water enter soil?
Water enters a soil through its pore spaces,
and thus knowing the bulk density and
condition of pore space is essential to
understanding how water gets into a given
soil. This is a matter of concern for ranchers
and farmers because how quickly or slowly
water enters the soils they steward determines
levels of runoff, and controlling runoff is a way
to mitigate drought and prevent erosion.
In New Mexico and Colorado the majority
of our rain events occur in the summer
and are characterized by high intensity
precipitation—lots of rain and/or hail in a short
amount of time. For producers this makes it
important that water enters the soil quickly,
so that it will be available to plants rather than
lost to runoff.
Glossary
Infiltration Rate
the rate at which water enters the pore
spaces in a given area of soil, often measured
in inches of water per hour.
Soil Water Component
In compacted soils, the infiltration is limited,
as the size and number of pores is limited.
Water instead flows off the surface of the
soil, carrying soil particles and organic matter
away and thus resulting in erosion. Soil
compaction can occur through the action
of animals, vehicles, and human foot traffic.
Soil can be compacted on the surface, and
this can be evident through the formation of
surface physical crust, or it can be compacted
below the surface. Subsoil compaction is
common in agricultural soils and is sometimes
called “plow pan,” referring to the effects of
agricultural machinery. Water may infiltrate
the surface of these soils but will not move
throughout the soil profile. Then, once the
surface layer is saturated, water will run off.
On ranches and farms in New Mexico and
Colorado, compaction is common along
access roads. This has led to surface runoff
and erosion problems that can become quite
severe. Hydrologist Bill Zeedyk offers ideas
for effectively addressing access road soil
compaction in his technical manual,”A Good
Road Lies Easy on the Land,” and some of his
approaches to restoration and erosion control
are included in the Quivira Coalition’s “Erosion
Control Field Guide.”