Reading Practice 7

[1] Living organisms have an important function in the formation of soil. The numerous animals and plants that live in the soil use minerals found there, and in turn create organic matter that aids in the translocation (movement) and aeration of the soil, and helps protect the soil from erosion. Various types of organisms which dwell in the soil substantially influence the soil’s chemical and physical characteristics. In fact, for mature soils found around the world, this important type of natural growth is thought to have the greatest direct impact on soil characteristics. For this reason, a soil scientist can understand quite a bit about the attributes of the soil in any given place simply by understanding what sort of flora the soil supports. Thus prairies and tundra regions, which have characteristic vegetation, also have mature soils.

 

[2] The quantity and total weight of soil vegetation typically exceed that of soil fauna. Far and away, the most common and smallest of the plants dwelling in the soil are bacteria. In favorable conditions, over a million of these tiny, single-celled plants can inhabit each cubic centimeter of soil. Beyond that of any other organism, bacteria allow rock or other parent material to undergo a gradual, yet regular transformation to the soil. Some microorganisms produce natural acids that immediately attack parent material, breaking it down and releasing plant nutrients. The second group of microorganisms decomposes natural waste (debris) to shape humus (nutrient-rich organic matter). The third group of bacteria inhabits the root systems of flora called legumes. Included in this are many well-known agricultural crops, such as alfalfa, soybeans, peas, clover, and peanuts. Legumes host bacteria within their root nodules (small swellings on the root) that converts nitrogen gas from their surroundings into nitrogen compounds that flora is able to metabolize in a process known as nitrogen fixation, which results in more fertile soil.

 

[3] There are other life forms that play a vital role in soil development. For example, in rather acidic soils where few bacteria can survive, fungi frequently emerge as the main decomposers of organic matter. More complex varieties of vegetation are also essential to the development of the soil. Trees, grass, and various other types of vegetation provide the bulk of the soil’s humus. The minerals released as these plants decompose make up an essential nutrient supply for succeeding generations of flora as for other soil organisms. In addition, timber can extend its roots deep within the soil and carry vitamins up from a long way under the surface. When the tree loses its leaves, or when it dies and decomposes, this will result in the enrichment of the soil with vitamins. Finally, timber performs the indispensable function of slowing water runoff and keeping the soil in place with its root systems, consequently combating erosion. The increased erosion that often accompanies the agricultural use of sloping land is mainly induced by eliminating its protecting layer of natural vegetation.

 

[4] Animals also have an effect on soil composition. The faunal counterparts of bacteria are protozoa. These single-celled organisms are the most commonly found members of the animal kingdom, and, like bacteria, more than a million can inhabit each cubic centimeter of soil at a time. Protozoa feed on organic matter and hasten its decomposition. The earthworm is in all likelihood the most essential among the soil-dwelling inhabitants. Under fairly favorable conditions, up to a million earthworms (with total body weight exceeding about 450 kilograms) may inhabit an acre of soil. Earthworms ingest large quantities of soil, chemically alter it, and excrete it as organic matter called casts. The casts form an incredible natural fertilizer. In addition, earthworms mix soil both vertically and horizontally, improving aeration and drainage.

 

[5] Under favorable climatic and soil conditions, insects such as ants and termites may also be numerous. In addition, local mammals such as mice, gophers, moles, and prairie dogs are occasionally present in sufficient numbers to have an enormous impact on the soil. These animals chiefly work the soil mechanically. As a result, the soil is aerated, broken up, fertilized, and brought to the surface, hastening soil development.