LaMotte Water & Soil pH - Manual (Page 3)

WHAT IS SOIL?
Soil forms the natural covering of the Earth and supports plant life. It is
formed by weathering, or the breakdown of rocks into smaller particles by
natural forces. Wind, rain, freezing and thawing are all important forms of
weathering. Weathering is a continual process, but it is slow, and the
formation of new soil takes hundreds of years. Therefore, it is important to
conserve existing soil and use it wisely.
Weathered rocks are not the only the components of soil. Soil also
contains nutrients necessary for plant growth and survival. These
nutrients come from weathered rocks, and from dead decomposed plant
and animal material. Plant and animal waste left in soil are decomposed by
bacteria and fungi living in the soil, adding nutrients to the soil. The
practice of plowing or spading plant leaves into the soil, or adding humus
to the soil, will also add nutrients. Humus, composed of decayed organic
material, not only adds nutrients to the soil, it helps improve the texture
and water-holding capacity of the soil.
Since there are many types of rocks, and varying amounts of vegetation,
many different types of soil are formed. Soil types are classified by the size
of the particles; clay particles are the smallest, silt particles are
medium-sized, and sand particles are the largest. Each type of soil has a
unique feel. Sandy soil feels gritty when rubbed between the fingers, silty
soil feels silky or powdery, and clay feels sticky and moist. Many soils are a
combination of these three particles, and are called loam. The percentage
of each type of particle in loam can be determined by measuring settling
rates; sand particles settle fastest, and clay particles settle slowest.
In addition to covering the Earth, soil provides the nutrients necessary for
plants to survive. Plants require many different nutrients. Some nutrients,
such as nitrogen, phosphorus, and potassium are required in large
amounts, while only small amounts of others, such as sulfur, iron,
manganese, and calcium, are necessary. It is important that these nutrients
are not only present in the soil, but that they are in a form available to the
plants. Availability is dependent upon several factors, particularly the pH
of the soil. For instance, if the pH is too high iron will not be in a form
plants can use; it will not be available to the plants.
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