Colorado Reader Feb. 2020: Soil, Water, and Air Stewardship | Page 2

Soil - MORE THAN DIRT!
We interact with soil every day, even when we aren’t thinking
about it! We walk on it, we dig into it, we build with it, and we
grow things in it. But what is soil? Is it just dirt that gets under
our fingernails and stains our clothes when we play in it? No!
Soil is a mixture of minerals, dead and living organisms, air,
and water. Soil is one of our most useful natural resources.
Soils are limited natural resources. That means that while
they are renewable because they are constantly forming,
they do so at an extremely slow rate. One inch of topsoil
can take hundreds or even thousands of years to develop.
A few ways soil can be negatively impacted are:
• Erosion – The wearing of soil by water,
wind, and human actions.
• Urban development – Moving soil around or
removing the soil to construct buildings and roads.
• Contamination – When harmful objects, chemicals, or
substances pollute the soil in a way that causes harm
to other living things or destroys the soil ecosystem.
• Compaction – The pressing together of soil particles
causing the soil to become hard and usually very dry.
What are the Layers of Soil?
Soil is made up of distinct horizontal layers; these layers are called horizons. Using the descriptions below, can
you identify the soil layers? Write the letter of the Horizon name next to each soil layer in the graphic.
A Horizon - The layer called topsoil; it is found below the O
horizon and above the E horizon. Seeds germinate and plant
roots grow in this dark-colored layer. It is made up of humus
(decomposed organic matter) mixed with mineral particles.
B Horizon - Also called the subsoil; this layer is beneath the E Horizon
and above the C Horizon. It contains clay and mineral deposits (like
iron, aluminum oxides, and calcium carbonate) that it receives from
layers above it when mineralized water drips from the soil above.
C Horizon - Also called regolith; the layer beneath the B Horizon and above
the R Horizon. It consists of slightly broken-up bedrock. Plant roots do not
penetrate into this layer; very little organic material is found in this layer.
E Horizon - This eluviation (leaching) layer is light in color; this layer
is beneath the A Horizon and above the B Horizon. It is made up
mostly of sand and silt, having lost most of its minerals and clay
as water drips through the soil (in the process of eluviation). Bonus: Can you
O Horizon - The top, organic layer of soil, made up mostly of
leaf litter and humus (decomposed organic matter).
name what this line
is pointing to?
_____________
R Horizon - The unweathered rock (bedrock) layer
that is beneath all the other layers.
2 - Colorado Agriculture in the Classroom