Introduction
Most Material in soil comes from a Bedrock below it. Soil has many
different layers (with himus-rich soil on top, sediment below, and
bedrock on the bottom) because of the way soil forms.
These layers are known as Horizons.
Horizons tell you how these layers are horizontal. There are 3 different
types of horizons. Each horizon is around a few centimeters to a few
meters in thickness. The first two layers is what really makes up soil.
Horizon A- This is the layer that contains the
Topsoil. The topsoil consists of more Humus than the other 2 horizons.
In this layer when water travels through it, it carries fine-grained
materials and drops it off in horrizon B.
Horizon B- this is the layer that is often known as
the Subsoil. In this layer clays and dissolved substances from horizon
A collect.
Horizon C- This layer consists of partially weathered bedrock,
this layer is usually the parent (adult) rock of the soil in horizon C.
Physical and Chemical Composition
Physical and chemical compositions of
the three soill horizons can change, depending on the way the soil
develops. There are many different ways that soil can be developed.
The most important factor controlling the way soil is developed is
Climate. The reason why is beacause climate has a control over other
factors. Like what kinds of plants can grow in that type of climate or
weather.Temperature also controls the types of chemical and physical weathering
that take place in soil. In order for soil to form a solid rock has to begin
weathering, weathering is also what plant growth depends on the most. But
in some places the process is very slow, so the soil will be less developed.
Soil in cold places seem to be less developde than soils in warmer places.
Farming
Soil can
be used for many different ways, one way is farming. In farming soil
is defined as a thin layre of very looes earth materials from weathered
minerals. Soil has a very inportant role in planting, because in order
to plant you need soil. It provides alot of nutrients and it also provide
air and water for plant growth.
The
breakdown of rock into smaller and smaller pieces is called weathering.
The rocks that are on the earths surface are undergoing weathering mostly
all the time. They do this by ither Chemiacl means or Physical means.
Chemical
weathering happens when minerals in rocks start to chemically change, and
then they began to decay. When rain increases it speeds up the chemical
weathering of minerals in rocks. This can be seen on graves, monuments and
lots of the statues in Central Park.Water takes a very important part in
in chemical weathering. When temperature increases it has a chemical reaction
that causes minerals to degrade. This is part of te raeson why hot, climates
have a highly weatherd landfoms, soils, and buildings.
Physical
Weathering Processes
Rocks
that have been broken down by another process other than chemical alteration
are physically or mechanically weathered. Arock broken into small parts
that shows more surface area of the origanl rock. Increasing the the surface
area of a rock will increase it’s weathering potential.
Earthworms
and animals cause a whole lot of weathering. They do this by burrowing through
the soil and then moving soil partticles around. This showsfresh surfeces
to continued weathering. Believe it or not, some kinds of tropical worms
travel at aproximatly 100 metric tons of soil per acer every year. Mostly
any animal the burrows through soil causes maechanical weathering. Ants,
mice, coyotes, and rabbits all contribute. When the animals mix and dig
often contributes to another type of weathering. This is called chemical
weathering.
There
are three different types of soil, they are Sand, silt, and clay. The spaces
between soil particles are called pores. The number of pores per unit volume
os soil is called Porosity.. Soil with large and numerous spaces between
particles has a high porosity. Soil with fewer and smaller spaces betweenn
particles has a low porosity. The porosity of soil affects the way that
water moves throgh the soil.
Horizon A: High Porosity
Horizon B: Low Porosity
Horizon C: Low porosity
Silt: Low porosity
Clay: Low Porosity
Sand: High Porosity
Here are some websites you can go to for more info on Soil
http://Go.hrw.com
Keyword:HSTWSF
Scilinks.org
Topic:Weathering
Scilinks Number:HSTE233
Topic: Rates of Weathering
Scilinks Number: HSTE235
Topic:Soil and climate
Scilinks Number: HSTE240
Topic: Soil Types
Scilinks Number: HSTE245
Teachers click here for some fun
soil activities!