” Soil is a natural body consisting of layers (soil horizons) of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and environmental processes that include weathering and erosion. Soil differs from its parent rock due to interactions between the lithosphere, hydrosphere, atmosphere, and the biosphere. It is a mixture of mineral and organic constituents that are in solid, gaseous and aqueous states.”
Soil particles pack loosely, forming a soil structure filled with pore spaces. These pores contain soil solution (liquid) and air (gas). Accordingly, soils are often treated as a three state system.Most soils have a density between 1 and 2 g/cm³. Soil is also known as earth: it is the substance from which our planet takes its name. Little of the soil composition of planet Earth is older than the Tertiary and most no older than the Pleistocene. In engineering, soil is referred to as regolith, or loose rock material. In agriculture this word is used to describe the thin layer of surface earth that, like some great blanket, is tucked around the wrinkled and age-beaten form of our globe.
The harder and colder earth under this surface layer is called the subsoil. It
should be noted, however, that in waterless and sun-dried regions there
seems little difference between the soil and the subsoil.
Plants, insects, birds, beasts, men,–all alike are fed on what grows in this
thin layer of soil. If some wild flood in sudden wrath could sweep into the
ocean this earth-wrapping soil, food would soon become as scarce as it was
in Samaria when mothers ate their sons. The face of the earth as we now
see it, daintily robed in grass, or uplifting waving acres of corn, or even
naked, water-scarred, and disfigured by man’s neglect, is very different
from what it was in its earliest days. How was it then? How was the soil
Learned men think that at first the surface of the earth was solid rock. How
was this rock changed into workable soil? Occasionally a curious boy picks
up a rotten stone, squeezes it, and finds his hands filled with dirt, or soil.
Now, just as the boy crumbled with his fingers this single stone, the great
forces of nature with boundless patience crumbled, or, as it is called,
disintegrated, the early rock mass. The simple but giant-strong agents that
beat the rocks into powder with a clublike force a millionfold more
powerful than the club force of Hercules were chiefly (1) heat and cold; (2)
water, frost, and ice; (3) a very low form of vegetable life; and (4) tiny
animals–if such minute bodies can be called animals. In some cases these
forces acted singly; in others, all acted together to rend and crumble the
unbroken stretch of rock. Adding amendments like peat moss, low temperature charcoal crushed, Stone meal, bone meal, and compost help to tailor the soil for the plant desired.
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