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Section 7.3 Guided Notes
Soil forms slowly as a result of _________________________ and
____________________ processes. Soil is the loose covering of _______________________
rock particles and _____________________ organic matter, called _______________, overlying
the bedrock of Earth’s surface, and serves as a _____________________ for the growth of
plants. It is the product of _____________________ of years of chemical and mechanical
___________________________ and _________________________ activity. The
___________ development process begins when weathering ___________________ solid
bedrock into _____________________ pieces. __________________ and other
___________________________ help break down organic __________________ and add
_________________________ to the soil as well as creating ____________________ for air and
water. As nutrients are added to the soil, its ________________ __________________, and the
soil’s _______________________ to hold water ____________________. While all soil
contains some ______________________ ______________________ in various states of
_________________, the amount varies widely among different ______________ of soil.
During the process of its formation, soil develops _______________. Most of the
volume of soil is formed from the weathered products of a _________________ rock, called the
____________________ _______________________. The parent material of the soil is often
the ______________________. As the parent material ___________________, the weathering
products rest on ______________ of the parent material. Over time, a layer of the
______________________ pieces of weathered rock develops _______________ the parent
material. Eventually, living organisms such as _____________________ and
__________________________ become established, and use ______________________ and
___________________________ available in the material. __________________________
seeps through this top layer of materials and _______________________ soluble
________________, carrying them into the _________________ layers of the soil. A soil whose
parent material is the local bedrock is called _______________________ _______________.
_________________________ ___________________ is soil that develops from parent material
that has been moved far from its original _______________________. Agents of
________________ transport parent material from its place of ________________ to new
__________________________. Over time, processes of soil formation transform these
deposits into mature soil layers.
Digging a deep hole in the ground will reveal a soil __________________. A soil profile
is a ___________________ sequence of soil layers. It can take tens of thousands of years for
distinct layers to form in a soil. A distinct layer within a soil profile is called a
___________________ _________________________. There are ______________ major soil
horizons in ____________________ soils.
Label Soil Layers Diagram
Read the definitions below, and then label the soil layers (called soil horizons) diagram.
O Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus
(decomposed organic matter).
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.
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).
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.
R Horizon - The unweathered rock (bedrock) layer that is beneath all the other layers.
Particles of soil are classified according to size as ________________, __________________, or
_________________, with clay being the _____________________ and sand being the
_________________________. The proportions of particle sizes determine a soil’s
_______________. Soil texture affects its capacity to retain _____________________ and
support plant ________________. Soil fertility is the measure of how well a soil can support the
growth of plants. Factors that affect soil fertility include ______________________________,
availability of ____________________ and __________________________, the
______________________ of microorganisms present, the amount of
______________________________ available, and the level of ________________________.
The minerals, organic matter, and moisture in each soil horizon determine its
___________________. Scientists use the ___________________ System of
_________________ __________________________ to describe soil color.
CONCEPT MAP FOR 5 FACTORS OF SOIL FORMATION
CLIMATE
TOPOGRAPHY
PARENT MATERIAL
BIOLOGICAL
ORGANISMS
TIME