|
|
|
|
Identification and Classification of Soil |
OBJECTIVES:
VOCABULARY: MATERIALS:
·
wand magnets
·
hand lens
·
beakers
·
measuring spoons
BACKGROUND: Soil is composed of organic matter and broken down rocks. The
organic matter is from other surrounding life that has started to mix with
the small rocks. Many soil dwelling organisms spend their lives
breaking down dead animals and plants, releasing nutrients for use by
growing plants. These decomposers, sometimes called reducers, are
responsible for the fertility of the soil. The constituents of soil are extremely variable in
size, shape and chemical composition.
The size of particles is one of the most significant
characteristics. Water
absorption, air movement, rate of solution and ease of tillage are a few
things that are affected by particle size.
The texture of soil refers to particle sizes and is
classified on an arbitrary scale.
It can be coarse, sandy, or clayey.
Sand would be about the size of sand, coarse would refer to soil
that is larger and clayey would be smaller.
You can also describe the structure of soil by how the soil
particles tick together. When
particles are rather porous and small, the soil is considered to have a
granular or crumby structure, which is characteristic of many soils high
in organic matter. Soil that
is lumpy usually sticks together. Sometimes
soil has magnetite in it, a magnetic mineral that is attracted to a
magnet. Humus, the partially decayed organic matter
accumulated in soils, is a dark-colored structure less material.
Making compost would simulate and speed up nature’s way of making
humus. Soil horizons can be different for high productive areas versus low productive areas. PRODUCTIVE A. contains more organic matter in most areas, most weathered and leached at
all levels, loose, easily
tilled, fertile
B. Yellow layer containing small quantities of clay
and easily penetrated by air, water, and
plant roots
C. slightly weathered, permeable, calcareous
NON PRODUCTIVE
A. light gray layer, low in fertility and difficult
to till
B. heavy clay layer impermeable to air, water, and
plant roots, massive stable aggregates of
small particles
C. heavy clay parent matter In a process called photosynthesis, plants use energy
from the sun to change carbon dioxide (CO2 - carbon and oxygen) and water
(H2O- hydrogen and oxygen) into starches and sugars. These starches and
sugars are the plant's food. Photosynthesis means "making things with light". Since plants get carbon,
hydrogen, and oxygen from the air and water, there is little farmers and
gardeners can do to control how much of these nutrients a plant can use.
The 13 mineral nutrients, which come from the soil,
are dissolved in water and absorbed through a plant's roots. There are not
always enough of these nutrients in the soil for a plant to grow healthy.
This is why many farmers and gardeners use fertilizers to add the
nutrients to the soil.
The mineral nutrients are divided into two groups:
macronutrients and micronutrients.
Macronutrients can be broken into primary and
secondary nutrients. The
primary nutrients are nitrogen (N), phosphorus (P), and potassium (K).
These major nutrients usually are lacking from the soil first because
plants use large amounts for their growth and survival.
The secondary nutrients are calcium (Ca), magnesium (Mg), and
sulfur (S). There are usually enough of these nutrients in the soil so
fertilization is not always needed. Also, large amounts of Calcium and
Magnesium are added when lime is applied to acidic soils. Sulfur is
usually found in sufficient amounts from the slow decomposition of soil
organic matter, an important reason for not throwing out grass clippings
and leaves.
Micronutrients are those elements essential for plant
growth which are needed in only very small (micro) quantities . These
elements are sometimes called minor elements or trace elements. The
micronutrients are boron (B), copper (Cu), iron (Fe), chloride (Cl),
manganese (Mn), molybdenum (Mo) and zinc (Zn). Recycling organic matter
such as grass clippings and tree leaves is an excellent way of providing
micronutrients (as well as macronutrients) to growing plants. Notice that all the components are ultimately
composed of chemicals. However, there are inorganic components that are "given" or specific to an
area. The ecosystem has to
build itself on soil (organic matter + rock).
Organic matter is carbon based, but rocks can be made of a variety
of chemical compounds which add character to a particular soil. Remember,
minerals make-up rocks, and minerals can be composed of elements or
compounds.
PROCEDURE:
1. Go over the Soil Formation
powerpoint.
Pass out the worksheet that will be used for both parts of the lab.
2. Activity--TESTING
DENSITY BETWEEN MINERALS, COMPOST AND TOPSOIL. Tell students "first we are
going to test the density of minerals, soil and compost."
Have a beaker of water ready for teams of students.
They will also need measuring spoons and three soil samples (can do
3 students together so two beakers per table)
·
Students will add 5 ml of
sand to the water and observe whether it sinks or floats
and record it on their worksheet (it should sink).
They can stir the mixture after they make their first observation.
·
They should then add 5ml
of compost (can be taken from the science garden) and record whether it
floats (it should mostly float).
·
Lastly they should add 5m of
topsoil (can be taken from the garden) and record whether it sinks or
floats (it should do both).
·
Have them tell you their
results
3.
Activity:
DETERMINING THE SOIL LAYER BY AMOUNT OF ORGANICS. Remove the water
from the tables and give the students soil samples in bags.
Student must leave the soil
samples in the bags. Just
observe through the plastic.
They can use hand lens to make observations.
For each soil sample the students
should
·
describe the sample (does it have plant
debris or animal remains in it? what color is it?)
·
based on their observations and the key
on the worksheet, hypothesize what soil layer the sample corresponds to
(O, A, B or C)
·
Have them tell you their results
They can then look at the soil from the school (in trays rather
than bags). They can touch
this soil. What layer do they
think it is from and why?
4.
Activity --
Students use a wand
magnet over the
outside of the soil sample bags to see if there is any that have
magnetite, a magnetic mineral.
If the soils have magnetite they will see small bits respond to the
magnet. The presence of
magnetite means that the parent rock may have been granitic.
Magnetite erodes out of the rock and is left in the soil.
final wrap up:
Ask students if
they remember the four main components of soil.
(Minerals, water, air and organic material).
What is compost
(only organic material).
Does decay happen naturally (yes just usually takes longer).
Remember, Soil
formation is complex! It takes
a long time to form so we need to take care of soil.
Adding compost helps keep the soils healthy.
They will get to put the class compost in the garden in the next
lab.
|