Soil and Plants Study Guide
Soil
Soil is the loose material in which plans can grow in the upper
layer of Earth. There are many types of soils (such as silt, sand,
and clay). Soils can be very different in color, grain size, and how
much water the soils hold. Soil is a mixture of four different
materials: weathered rock that contains minerals, humus, air, and
water. Soil provides nutrients for plants to grow. Soil is a natural
resource and should be conserved (saved and taken care of).
Vocabulary
Topsoil: Topsoil is a natural product of subsoil and bedrock. It is
the top layer of soil made up of the smallest grains and the most
humus.
Loam: Loam is a type of topsoil. It is rich with lots of humus. It
has a lot of water and air. This makes it good for planting. Most
farm soils are loam.
Humus: Humus is a type of soil that is mostly found in topsoil. It
is made up of decayed parts of once-living things. It is a rich type
of soil
Subsoil: Subsoil is the layer of soil just below topsoil. It is above
the bedrock layer.
Bedrock: Bedrock is the solid rock that is under soil.
Weathering: The process by which rock is worn down and
broken apart. Bedrock gets “weathered” and breaks down into
smaller grains of soil.
Soil Layers (from top to bottom)
Topsoil
Subsoil
Bedrock
Clay is made up of very small grains. When clay dries after a
rainfall, it often forms hard clods. Clods break up and feel like
powder. But, clay traps water and stays so wet and heavy that it is
hard for roots to grow there.
Sand is also in soil and is a type of soil. It is very loose grains of
worn rock. Very sandy soil does not hold water. Water drains out
very quickly.
Soil Conservation
Key terms to know:
Natural Resource: a material found in nature that living things
use.
Conservation: saving resources by using them carefully.
Strip cropping: planting strips of thick grass or clover between
strips of crops.
Contour plowing: planting rows of crops around the sides of hills
instead of up and down.
Tilling: turning over soil, the process of turning over soil
Key Ideas:
Read about conservation, strip cropping and contour plowing
on page C76.
What are two ways we can conserve soil?
Strip cropping
Contour plowing
How does strip cropping work: How is it helpful?
Farmers plant strips of grass between crops to keep the water in the
soil. This stops the soil from washing away.
How does contour plowing work? How is it helpful?
Farmers plant rows of crops around sides of hills instead of up and
down. This keeps water from running off in a straight line, so soil
isn’t washed away.
Soil Vocabulary
Topsoil
A natural product of subsoil and bedrock.
It is the top layer of soil made up of the
smallest grains and the most humus.
Loam
A type of topsoil. It is a rich soil made up of
of sand, silt and clay. This makes it good for
planting.
Humus
Is made up of decayed parts of once-living
things. It is mostly found in topsoil. It is a
rich type of soil with lots of minerals and
nutrients.
Subsoil
The layer just below the topsoil. It is
above the bedrock layer.
Topsoil
Bedrock
The solid rock under the soil.
Bedrock
Clay
Is made up of very small grains. After a
rainfall, clay traps water and stays wet
and heavy. When dry, it forms hard clods
and cracks. This makes it difficult for
roots to grow in clay.
Sand
Is a type of soil. It is very loose grains
of worn rock. Very sandy soil does not
hold water. Water drains out very
quickly.
Weathering
Is the process by which rock is
worn down and broken apart.
Contour Plowing
Plowing on “contour” or gentle slopes.
Strip Cropping
Planting strips of grass or clover
between crops is one technique for
reducing erosion.
Crop Rotation
Crop Rotation is changing the type of
plant grown on a particular piece of
land from year to year or season to
season. This prevents one crop from
using up certain nutrients in the soil
year after year.
Erosion
The wearing away of a surface by
physical means.