The A horizon or topsoil is thus also called the humus layer. 2) A Horizon – (Topsoil)įound below the O horizon, it has a dark brown color as it contains the maximum organic matter of the soil. The O horizon is thin in some soil, thick in some others, or absent in the rest. Due to high organic content, this layer is typically black brown or dark brown. This layer is the uppermost layer of the soil rich in organic matter, such as the remains of plants and dead animals. Immature soils lack some of these layers. These layers or horizons are represented by alphabets O, A, E, C, B, and R. The sizes of rock particles in a soil have a very important influence on the properties of that soil.There are six different layers or horizons that make up a mature soil profile. All these soils have different proportions of rock particles of different sizes. So, depending on its composition, a soil can be classified as sandy soil, clayey soil or loamy soil. The main rock particles present in the top-soil are sand, clay and silt. In a good top-soil, gravel is present in very small amount. The amount of gravel present in a good top-soil is very small. (4) The largest sized rock particles present in soil are called gravel. And because of its large sized particles, sand is coarse to touch. Being quite large, sand particles can be easily seen by us. (3) The rock particles in soil which are larger than silt particles form sand. The size of silt particles is bigger than that of clay particles but smaller than those of sand particles. Actually, the size of silt particles is in-between that of clay and sand. Due to its slightly bigger sized particles, silt is not so smooth. (2) The rock particles in soil which are a little larger than clay particles form silt. Thus, silt is made up of rock particles somewhat bigger than that of clay. Because of its very small particles, clay feels smooth to touch. On the basis of their sizes, the rock particles present in soil can be divided mainly into four groups: Clay, Silt, Sand and Gravel.ġ) The smallest rock particles present in soil form clay. The rock particles present in soil are of different sizes and chemical compositions. The soil is made up of six components: Rock particles (of different sizes), Minerals, Humus (Organic matter), Air, Water and Living organisms. Sub-stratum is made up of small lumps of broken rocks (or stones) formed by the partial weathering of bed-rock (or parent rock).īelow the C-horizon we have unweathered solid rock called bed-rock (or parent rock).It is this bed-rock (or parent rock) which has produced the soil over a long period of time. The layer of soil which is just below the sub-soil is called C-horizon. Due to this, sub-soil is much less fertile as compared to the top-soil. The sub-soil has very little humus (decayed organic matter). The roots of some of the trees are, however, able to reach sub-soil. The sub-soil contains very little living organisms. Sub-soil is also lighter in colour than the top-soil. It is somewhat harder and more compact than the top-soil. The sub-soil is made up of slightly bigger rock particles than that of top-soil. The layer of soil which is just below the top-soil is called B-horizon. The nature of any soil depends on the rocks from which it has been formed and the type of vegetation that grows in it. These tiny rock particles then mix up with humus to form fertile soil. In weathering, rocks are broken down very slowly by the action of sun’s heat, wind, rain, flowing river water, etc. Soil is formed from rocks by the process of weathering. Humus contains nutrients (like nitrogen and phosphorus, etc,) which are needed by the plants for their growth. The organic matter formed by the decomposition of dead plants and animals by the micro-organisms (like certain bacteria and fungi) is called humus. The process by which huge rocks are broken down into small particles by the action of sun’s heat, wind, rain and flowing river water, etc. (5) Soil is used to make earthenware or pottery (such as matkas, surahis, etc.), crockery (cups and plates), toys and statues, etc. (4) Soil is used to make bricks and mortar for building houses. Soil is also used to grow mulberry trees for rearing silkworms which provide us silk for making silk clothes. (3) Soil is used to grow cotton plants which give us cotton clothes. (2) Soil is used to grow trees for obtaining wood for building purposes (timber), for burning as fuel (firewood) and for making paper.
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