Organic Soil and Analysis

Soil formation is a slow process, estimated to require 10,000 years or more to form one foot of depth. The best soils provide 10 feet or more of effective depth for root zone.

Rocks are variable in composition but contain several minerals such as feldspars. micas, apatite, hornblend and others that are important in forming soils. As the solid rock disintegrates, the minerals are liberated to dissolve partially in water.

Taking orthoclase feldspar mineral as an example, one of the results of the dissolving action of water is some soluble potassium. Another result is the freeing of some silica which may become ordinary sand. Still another product of the reaction with water is the clay material of the soil, a new mineral derived from the feldspar-water reaction.

These reactions are typical of those that account for two important mechanical soil parts, sand and clay. The third mechanical constituent is the silt which is composed of tiny pieces of minerals ranging in size from live hundredths of a millimeter to live thousandths of a millimeter in diameter. Clay particles are smaller than this range and sand particles are larger, up to one millimeter in diameter. The relative proportion of sand, silt and clay, determines soil texture.

Breaking Down Soil – A Part of Systems

The disintegration of rocks is partly physical and partly chemical. When a glacier grinds rocks to flour, or when the alternate heating and cooling breaks big rocks into little ones, those are physical processes. Hydration, solution, and oxidation are chemical processes.

After rocks are disintegrated and the minerals undergo various changes by chemical reactions, the fine materials are subject to some sorting and redistribution by wind and water. Streams and lakes redistribute the sand, silt and clay, sometimes leaving sand predominantly in one location and perhaps clay mostly in another. Or the wind picks up silt and carries it far from the original source and covers the earth sometimes several feet deep with fine material. This then becomes a fertile and highly productive loess soil.

Soil is not only a mass of minerals in various stages of weathering that gives sand, silt and clay particles, but it contains two to four per cent, or more (by weight) of organic matter that is mostly humus, partially decomposed remains of plant roots, and various kinds of litter and organisms. The humus of the soil, chemically. is largely lignin, hemicellulose, and protein materials. The lignin in part, at least in combination with the protein and the humus mass, is partly in combination with the clay. This humus-clay combination takes on a sponge-like structure and forms water-stable granules, until, with abundance of humus as on the forest floor, the whole mass of soil becomes an accumulation of granules and crumbs, readily permeable to roots, water, and air – an ideal condition for supporting plant growth.

Soil is never an inert mixture of minerals and organic matter. It is a living system full of bacteria, fungi, and animal organisms such as earthworms, ants, and arthropods, all of which contribute something to the quality of the soil. These organisms decompose the organic matter and help mix the minerals and humus of the soil to form the granules. The larger organisms. such as ants and earthworms, make channels and burrows through the soil that are effective in admitting air and water and that provide openings for roots to penetrate.

Continued with Organisms Liberate Nutrients for Plants

By R Stephenson

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• Soil Testing – What’s Your Soil Flavor?
• Know Your Garden Soil
• Tips on Building Garden Soil
• Soil pH Makes the Difference