"The earth is the mother of us all - plants, animals and men. The phosphorus and calcium of the earth build our skeletons and nervous systems. Everything else our bodies need except air and sun comes from the earth." -Henry A. Wallace, in the Foreword to "Soils and Men," the 1938 Yearbook of the United States Department of Agriculture.
Without soils, no life could exist on earth. The lowly bacterial cell and the massive pachyderm both owe their being to this basic stuff of life. A bird in flight, a mole burrowing beneath your lawn, borers eating blindly into the heart of a great oak - all are linked by their common dependency on the elements of existence they draw from the soil.
Of earth's living creatures, man alone modifies the land to better suit his ends. Not satisfied with soil as he finds it, he tears its surface, incorporates organic and mineral materials and alters age-old structures. He often keys his actions to two false but widely held ideas: 1, that soils are simply clay and decaying vegetable matter - a mechanical support for plants - and 2, that the easy-digging quality of the soil means more than its chemical-biological quality. The error of this overall viewpoint was thrown into sharp focus not so many years ago by the controversy concerning the use of synthetic chemical soil conditioners. These products often made soil easier to till but with no resulting improvement in quality of plant growth. The "organocultists", those who believe only in organic gardening, have much to say about all this.
Tips on Types
Soil type is important. Type is determined largely by texture, a word often used in the wrong sense. It means simply particle size, such as fine sand, gravel, silt, clay, and so on.
Particle sizes in soils range something like this (mm = millimeter; 25 millimeters equal one inch):
Clay - 002 mm or smaller
Silt - 002 mm to .05 mm
Fine sand - 05 mm to .25 mm
Sand - 25 mm to 1.0 mm
Gravel - 1.0 mm to 32 mm
Stones - over 32 mm
Organic matter in soils may range in size from as large as entire plants that have been dug under to as small as humus particles so fine that they form colloidal solutions. (In a colloidal solution the minute particles do not settle out, but float indefinitely.)
Based on the preceding information, here is a soil classification according to particle size:
Stony loams: soils containing more than 50 per cent stones over 1 inch in diameter. If remainder is sufficiently fertile, this soil type may have gardening value, although it will be hard to work.
Gravels: soils with over 50 per cent gravel and much sand. Practically no garden value.
Sands: soils with more than 75 per cent sand. Low garden value.
Fine sandy loams: soils with 50 to 75 per cent fine sand mixed with much silt and some clay. Fairly good garden soils.
Sandy loams: soils with 50 to 75 per cent sand and much silt, some clay. Among the better light garden soils.
Loams: soils with 35 to 50 per cent sand mixed with much silt and some clay. Most of the better garden soils fall in this class.
Silt loams: soils with more than 50 per cent silt and less than 15 per cent clay. Are too "tight" to be good soils without some modification.
Clay loams: soils with 15 to 25 per cent clay, much silt and little sand. Usually are good garden soils if not worked when wet.
Clays: soils with more than 25 per cent clay, usually with much silt. Can be good if handled properly.
Mucks: soils with 15 to 25 per cent partially decomposed organic matter with much clay and silt. Good for certain crops, but modification is usually needed for general garden use.
Peaty loams: soils with 15 to 35 per cent organic matter mixed with much sand and some silt and clay. If acid, are good for broadleaved evergreens.
Peats: soils with 35 per cent or more organic matter, mixed with some sand, silt and clay. Need more mineral matter to be suitable for garden use.
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