Land is the part of the world not covered by the oceans, while soil
is a mixture of minerals, organic material, living organisms, air, and water.
Soil is a thin covering over the land.
The five major components of soil are mineral, organic material, living
organisms, air, and water.
Soil is formed by the physical fragmentation and chemical changes
in the parent material through a process known as mechanical and chemical
weathering.
Physical processes include freeze and thaw, glaciers, wind, and moving
water. Chemical weathering includes oxidation, hydrolysis, and the chemicals
released during growth of lichens and the decomposition of dead and decaying
material.
Other characteristics that determine a soil's usefulness include the
size of the particles, or texture, the way the soil clumps together, or
structure, its moisture content, biotic content, and chemical composition.
Soil composed of various-sized particles
has spaces for both air and water and allows excess water to drain out.
Soil composed of uniformly small particles has less space for air and water
will not drain out. Soil with only large particles has a tendency to lose
all of the water it receives. Since roots require air, water, and good
drainage, the soil with the various-sized particles would be better able
to support crops.
A soil profile is a series of horizontal
layers of different chemical composition, particle size, and amount of organic
material.
Erosion is the wearing away and transportation
of soil by water or wind.
Soil conservation practices include contour farming, in which tilling
is performed at right angles to the slope of the land; strip farming, in
which strips of closely sown crops like wheat are alternated with strips
of row crops like corn; and terracing, in which level areas are constructed
at right angles to the slope to retain water.
Other uses of soil include grazing, wood production,
wildlife production, and recreational purposes.
