Caso 2 - Background Information
Once you step out onto a piece of ground, you step out onto a
very active piece of real estate. Soil is not just a piece of
dirt. Soil is a complex system composed of living and nonliving
material spread as a very thin layer over the entire surface of
the planet we call earth.
Soil is not just the surface, however, but the entire depth
as it affects plant growth. Soil must provide nutrients, water,
and air and helps to support the plant.
Four major components of soil
The part of the soil we spend most of our time talking about
is the solid part or mineral matter. This solid matter makes up
about 45 percent of what we call soil and is composed of three
particles: sand, silt, and clay. Equally important, however, are
air and water. The two together account for about 50 percent of
soil. The percent of each depends on how much of the pore space--the
space between solid particles-is occupied by water at the time.
Finally there is organic matter. Depending on the soil type, about
three to five percent of soil is composed of organic matter.
Particle size has much to do with a soil's drainage, tilth, and
nutrient holding capacity. Although particle size seems to be
uniformly categorized as small, there is a great difference is
size. The difference can affect soil quality. If a particle of
sand were the size of a basketball, then silt would be the size
of a softball, and clay would be the size of a golf ball.
Soil type descriptions
People describe soil types in all kinds of ways such as heavy,
light, sandy, clay, loam, poor, or good. Soil scientists describe
soil types by the proportion of sand, silt, and clay particles
present. The texture of the soil is determined by the blend of
these various sized particles. By classifying soils in a particular
site, you can help to determine what types of problems you might
encounter when trying to grow plants. It is possible to change
the texture of soils through the addition of various amendments
in specific amounts. Changing composition or texture can help
in providing the proper conditions needed for plant growth that
might not have existed before.
More about sand, silt, and clay
Sand is the largest particle in the soil. When rubbed between
the thumb and finger, it feels rough and gritty. This is because
it has sharp edges. Soils with large amounts of sand are called
light textured. It has little nutrient holding capacity.
Silt is a soil particle whose size is between sand and clay.
These particles feel smooth and powdery. When wet it feels smooth
but not sticky. If silt is rolled between the fingers, it will
break up before a long ribbon is formed.
Clay is the smallest of particles. Clay is smooth when dry and
sticky when wet. When clay is rubbed between thumb and finger,
a long ribbon can be formed. Soils high in clay content are called
heavy soils. They have a high nutrient holding capacity.
Soil for gardening indoors
When growing plants indoors in containers, soil right from the
garden should not be used if you expect good results. The soil
usually contains weed seeds, disease organisms, and drains poorly.
If you want to use soil from the garden to illustrate how different
soils might affect the growth of plants, it must be mixed with
other things or amended. A suggested mix using soil is:
The amendments will help to provide the drainage and aeration
needed for good plant growth. Even better indoor growing media
are the artificial soils or soilless mixes. They are called artificial
because they contain no soil but are made up of peat, perlite,
vermiculite, and nutrients in various percentages. They have many
advantages over soil. They are clean, lightweight, provide for
excellent drainage, and easy to obtain. They are excellent for
growing most plants indoors in containers. Soilless mixtures are
available under several trade names such as Jiffy mix, Redi-earth,
Pro mix, and Sunshine mix. When using soilless mixes be sure to
pre-moisten them before filling your container. Also, because
artificial mixes contain no soil, they don't have a great deal
of nutrient holding capacity. Therefore, you will need to fertilize
plants regularly to maintain adequate nutrients in the soil.
Students can bring in soil samples from their own gardens. These
samples can be visually compared and notes made on how they differ.
A soil collage can be made using the soil samples that students
bring to class. These samples can be put into plastic sandwich
bags and attached to a bulletin board to note visual differences.
Soils that are brought to class can be dissected. Students can
physically separate and sort the samples into their components
and put similar items into piles. They will be able to see differences
in soils brought in from different areas of a neighborhood. Also
they can work up percentages of different items against the whole.
Soils that are brought in can be separated out in to the particles
that make up the soil by putting a cup of soil into a quart jar,
adding water to one inch of the top, sealing the jar, shaking
it vigorously, and letting it sit. The heavier particles (sand)
will settle out first, followed by the lighter particles. This
will result in bands or layers of various thicknesses. Soils from
different areas will produce different sized bands depending on
the percentages of the different particles present. With this
activity the students can produce graphs, charts, and figure percentages.
The actual process of soil mapping consists of walking over the
area at regular intervals and taking notes on soil differences
and all related surface features such as slopes, land use, vegetation
types, and other features.
A school soil map can be developed as a class project by systematically
surveying and taking notes of features on the grounds. Before
starting, establish a pattern or grid (divide area into units)
so it can be easily transferred to paper. In addition to physical
features, soil samples can be taken at regular intervals. These
samples can be separated into sand, silt, and clay as was done
in previous activities. Students can see if the percentage of
each component changes in the area that is being surveyed.
Composting takes advantage of the natural cycle of plants living,
dying, and decomposing to pass their vitality to new generations
of plants. Compost, the end product, is a valuable source of nutrients
for plants that also helps to improve the texture and fertility
of the soil.
There are many different types of materials that can be used
in compost, and each has its own good and bad points. Think of
compost as the soil's diet. The diet should be balanced between
materials that are strong in nitrogen and those strong in carbon,
between wet and dry materials, and between acidic and basic materials.
It is important that certain elements be provided. A ready-made
compost is created based upon the compost maker's assumptions
regarding what nutrients the soil needs and what materials are
available to the compost maker. The whole composting process starts
with the natural interaction of organic materials and microorganisms.
There are four basic ingredients in a compost pile:
Carbon, which provides the energy food for microorganisms
Nitrogen, which provides the protein microorganism need to
break down the carbon
Water and oxygen, which microorganisms need in large quantities
in order to do their job efficiently.
The basic compost pile consists of layers of organic matter,
sprinkled with a little soil and fertilizer, kept moist and turned
to introduce oxygen. The composting process can be hastened by
making the size of the material added to the pile small and by
Composting with critters
Studying about composting in the classroom can be made more exciting
by utilizing one of nature's best composters, the redworm. Redworms
lend themselves well to indoor units that can be used to integrate
all aspects of the curriculum. Science, math, nutrition, reading,
and art can all be integrated into a worm composting unit of study.
Worm bins are easy to set up and will not produce objectionable
odors when managed properly.
Basic principles of worm composting is to start with a container.
The container can be any size and made of any type of material.
Shallow (eight to nine inches) containers are best. Be sure there
are drainage holes in the bottom and aeration holes on the side.
Be sure to cover these holes from the inside with fiberglass screen
or old pantyhose to keep the worms in the box. Worms need bedding
to live in. The best and easiest to use is old shredded newspapers.
It takes about four to six pounds to fill a 2" by 2"
box. Moisture is also critical. Worms need it to help them breath.
Also keep in mind that a worm is about 75 to 90 percent water.
Pre-moisten the bedding before introducing worms. A general rule
of thumb is to use a ratio of three parts water to 1 part bedding.
So , if you use four pounds of shredded newspaper, you need to
add 12 pounds of water (1 pint = 1 pound).
The best worms to use are called red wigglers. These worms can
handle the warm temperatures of a classroom very well and thrive.
How many worms you need to start your worm composter depends on
the amount of garbage you think you will generate each day.
Generally, it takes about two pounds of worms to consume about
1 pound of garbage a day. Once established, worms are heavy feeders.
Worms do best at temperatures between 55 degrees F and 75 degrees
F. Worms will eat a variety of vegetable waste. Meat waste should
not be used in the bin. General maintenance consists of monitoring
the moisture levels (don't let it get too dry), providing food,
keeping it at the proper temperature, and occasionally removing
the castings (worm manure) that is produced and replacing it with
fresh bedding. The castings that are produced can be used in various
science related projects dealing with plant nutrition. A variety
of good reference manuals are available to help with class activities
and worm biology.