A fertile, productive soil is essential to successful gardening. A knowledge of soils and soil fertility should help improve one's gardening.
The typical mineral soil is composed of rock particles, organic matter, water, and air. The solid particles make up about 50 percent by volume, and the water and air each occupy about 25 percent. The exact percentages vary, depending on the nature of the soil and on whether the soil is wet or dry. In addition there are soil microorganisms and plant nutrients in solution.
The rock particles differ greatly in size and are classified as sand, silt, or clay. Sand particles are visible to the unaided eye, and their size ranges from 2.0 to .05 mm. Silt particles are visible under an ordinary microscope and range from .05 to .002 mm. Clay particles are extremely small, less than .002 mm., and can be seen only under an electron microscope.
The term "loam" is applied to a mixture of ingredients, and the terms "sandy loam," "silt loam," and "clay loam" are applied, depending on the texture.
Clay soils are likely to present the greatest problem for gardeners. The very small particles are platelike and become extremely sticky when wet. If such soils are cultivated when wet, large, hard clods result. If the soils are properly handled, the small clay particles adhere in granules or crumbs. This increases the penetration of water and air. Fall plowing or rotovating improves the granular structure, for freezing and thawing action during the winter causes the large clods to break down into granules.
Organic soils are derived from the decomposition of organic matter. If they contain 65 percent or more of organic matter, they are called peat soils; if 20 to 35 percent, muck soils. Peat soils are termed sedge or sphagnum, depending on the source of the organic matter. Compared with mineral soils, highly organic soils are usually low in plant nutrients.
Gardeners must generally start with disturbed soils of low fertility, because the topsoil, characteristic of farm fields, was removed or covered with subsoil during the construction of the home. Fortunately, the productivity of any soil can be improved.
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