THE NATURE AND FUNCTION OF SOIL“The growth of most plants is impossible without soil. Soil tea

THE NATURE AND FUNCTION OF SOIL“The growth of most plants is impossible without soil. Soil teams up with sun and rain to provide our food and clothing. Besides fish and water cultures, there is no other source of food than the crops grown on soil, and it is obvious that fish and water cultures can provide only a small fraction of the food that people need. Our survival depends on the conservation of the body and the fertility of the soil. We gauge, therefore, the value of the soil by its capacity to produce crops.A green plant has the ability to combine carbon dioxide and water from the ground into sugar, other carbohydrates and fat by the process called photosynthesis. Light furnishes the energy necessary for this reaction. Nitrogen, sulfur and phosphorus are required for the synthesis of proteins along with carbon, oxygen and hydrogen. Several other elements are needed for essential plant functions.A green plant is made up of about 80% water and 20% dry matter. The largest part of the dry matter is composed of the elements hydrogen, oxygen, carbon and nitrogen which occur in air and water, while the rest consists of a great variety of elements that originate in the soil. In spite of the small amounts of these components, they are absolutely essential and the complete absence of only one of them makes plant growth impossible.As a medium for plant growth, soil performs four functions:It serves to anchor the roots.It supplies water to the plant.It provides air for the plant roots.It furnishes the minerals for plant nutrition.———Soil consists of solid particles, water, and air and, in addition, contains a teeming population of minute plants and animals. The solids are both mineral and organic. The mineral particles are classified according to their sizes into gravel, sand, silt, and clay. The organic matter consists of fresh plant and animal residues, which are readily decomposed, and of more stable humus. These soil particles do not lie disorganized side by side but are usually associated into smaller or larger groups. These aggregates may be small crumbs or large clods.Of the solids, clay and organic matter are of major importance in the nutrition of plants, since they are chemically active. Gravel, sand and silt are largely inert and contribute little to plant nutrition. Over many years, however, some of these particles weather to release nutrient elements that are held by clay and organic matter.PORE SPACEThe pore space between the solids is taken up by water and air. The water might more appropriately be called a solution because it contains small quantities of numerous minerals. These serve as nutrients for the plants.Air takes up that part of pore space not occupied by water. As the water content increases, the air content decreases. The plant roots require oxygen for their normal functions just as the above-ground plant parts do and as animals breathe. In respiration, plant roots use oxygen and give off carbon dioxide. For this reason, soil air usually contains less oxygen and more carbon dioxide than atmospheric air does. A continuous replenishment is necessary to keep the oxygen content sufficiently high. Large pores and an intermediate moisture content are helpful for this.Millions of microbes live in each ounce of fertile soil. Without them soils would be inactive and soon lose their capacity to support plants. Microbes help to bring plant nutrients into available form and they make soil crumbs stable and resistant to erosion. Creating a hospitable environment for microbes in the soil is an important task of the farmer. Yield and composition of crops depend to a large extent on the properties of the soil. Humans, who eat these crops and the meat from the animals raised on these crops, are truly a product of the soil and reflect in their bodies – and minds – the wealth or the poverty of this land.”Kohnke & Franzmeier, Soil Science Simplified, 4th ed. -- source link

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