LaMotte Soil Texture - Manual (Page 4)

WHAT IS SOIL?
Soil is an important natural substance. Not only does it make up the
natural covering of the earth, it also supports most plant life. Think
what the world would be like without soil or the plants that grow in
soil. There would be no trees, flowers, fruits or vegetables.
Soil is formed over a long period of time from natural forces acting on
rocks and vegetation, a process called weathering. Weathering results in
different size particles that create the texture of soil. You can tell
whether soil is mostly sand, silt or clay by touch. An abundance of sand
gives the soil a gritty feel when rolled between the fingers. Soil with a
high silt content feels silky to the touch like talcum powder. Moist clay
makes soil feel sticky. The soil scientist can distinguish these various
types of particles according to their size; clay particles are the smallest,
silt particles are medium sized and sand particles are the largest. Soil
particles can also be determined by their different settling rates in a
solution.
Soil is composed of a mixture of mineral matter, organic matter and
humus. These materials help to improve the texture and saturation level
of the soil so air, water and nutrients are more easily available for the
plants. Plants absorb nutrients from these materials through small root
hairs and then use the nutrients to create new plant tissue and for
reproduction.
PLANTS AND SOIL
Plants require nutrients to survive and grow. Nitrogen, phosphorous and
potassium are critical to the plants, as are smaller amounts of sulfur,
iron, manganese, calcium, boron, copper and zinc.
It is not only critical that the nutrients are in the soil, but that they are
available to the plants. The availability of nutrients is highly dependent
on the pH of the soil; if the pH is not in the proper range the plants
will not be able to pull the necessary nutrients from the soil. Proper pH
ranges vary from plant to plant.
If soil lacks one or more nutrients, the plants develop mineral
deficiencies, which are signified by spots on the leaves, dead areas along
the leaf margin or stunting of the plant.
Man-made chemicals that are used to control weeds, insects and disease
should be handled with care. Their effect on other living things should
be carefully studied to make sure that they don’t interfere with the
natural process.
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Figure 1.
Adding Dispersing Reagent
40 mL
10 mL