UDK -63(631.427)

Soil as an essential component

Nurtaeva A – student of  the group AP12-2k

Toleshova M.T. – senior teacher

Kazakhstan, Shymkent

M.Auezov SKSU

 

Soil formation. Soil is produced from rock  by the process of weathering and by the activities  of plants, animals, and man. Primitive or igneous rocks, formed  by the soil deification of the magma  in the process of the cooling of the earth consist of aggregates  of mineral  crystals  which are  large or small according to the rate  at which cooling  took place. Each mineral is a chemical compound with specific chemical and physical  properties. As soon as igneous rocks  are exposed to changing  temperatures, moisture, etc. slow processes of disintegration and decomposition  begin.

            The weathering of a rock is generally due to a combination of physical and chemical actions. The weathered  products of rock alone do not constitute a soil. Plants establish themselves  very soon after weathering  begins, and  the mineral material thus becomes mixed with plant remains. These remains, in the process of decay, form and addition to the  products  of rock weathering. Soil is therefore  a mixture of organic and inorganic material containing  a large and  complex population  of living  things.

            The general character  of a soil depends to a considerable extent on the nature of the parent material. Thus a coarse-grained sandstone will generally produce a sandy soil, and a stratum of shale a “heavy” soil.

            Soil and Subsoil. Natural soils that have been long undisturbed are composed of rather clearly defined layers or “horizons”. Soil scientists distinguish  three main horizons the uppermost(A), from which material has been removed by leaching; the second (B), in which has been deposited  some of the material removed from (A); and the third (C), which consists of the parent material, e.g.. the partly  disintegrate  rock.

            The top soil is dark because of its high  content  of decaying vegetable matter (human) while the subsoil  varies  from reddish or yellowish  to a pale grey tint. Another usual difference is that the top soil is coarser  grained than the subsoil, the difference being caused by the washing  down of a proportion of the finer clay and silt particles.

            In general the top soil will be richer in nitrogen and phosphate than the subsoil, since  manures and fertilizers  are largely held in the former, but the subsoil  may frequently contain more potash.

            Soil particles. Typical soils (excepting peats and black fen types) are composed largely of particles and fragments of mineral matter. We must remember that these particles  are not all free one from another- indeed it is  obvious  that they are often bound together to form clods or crumbs. Nevertheless the character of a soil  depends  very much  upon the sizes of the particles  of which  it is composed.

            An important distinction is to be drawn  between sand and silt on the one hand and clay on the other. The coarser fractions in general form the “skeleton” of the soil.

            Primary elements. Of the eleven essential elements obtained from the soil by plants, six are used in relatively large quantities.

            They are nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. Because they are used by plants in relatively  large amounts they are sometimes called the primary elements. Plant growth may be retarded  because these elements  are lacking  in the soil, because they become available too slow, or because they are not balanced  by other nutrients. This is very often true with nitrogen.

            When nitrogen, phosphorus and potassium are artificially applied to the soil, they are usually  added as farm manure and especially as commercial  fertilizers. Therefore, they are often called fertilizer elements. In the same way calcium and magnesium are applied as lime and are called lime elements. Sulphur  usually goes into the soil as an incidental  ingredient of such fertilizers  as farm manure, superphosphate, and sulphate  of ammonia.

            Microelements. The other nutrient elements (iron, manganese, copper, zinc and boron) are used by higher plants in very small amounts and therefore  are sometimes called trace or microelements. These elements are just as important for the growth of plants as the primary elements.

            Fineness of Soil particles. We shall examine that part of the soil which is cultivated and which is called the top soil.

            What are the effects of the constant ploughing, harrowing, rolling, and other operations of tillage on this portion of the soil? Examine a handful of soil. You will see that it contains particles  of  various sizes. Small stones, gritty particles, and a certain amount of very fine earth will be present. Rootlets will also be seen and the mass will have an earthy smell. This is due to the presence of vegetable matter, the dark stuff that coast all the soil particles. Soils are  classified according to the fineness  of the particles  present.  The coarse particles are those of gravel and sand.

            Soils in which these predominate  are not fertile, they cannot retain water and contain little plant food. The finest particles in the soil are the clay particles. As the proportion of these increases  the nature  of the soil change. If the soil is mostly sand but has sufficient clay and vegetable matter, it may have some value as a market garden. With  more clay and other favourable  conditions potatoes can be  grown as on sandy loams. Loams are soils with sufficient  sand, clay and vegetable matter.

            When the proportion of clay is very large, then the soil becomes more difficult to cultivate. Often such soils  have to be  drained. They are more suited for crops such as wheat  and mangels. When they are too difficult or too expensive  greatly improved by applications of lime.

            By cultivating the soil its surface area is greatly increased. It can absorb water to a greater  extent; air can enter and bring about necessary chemical changes; the plant root have not to draw the food they require  from the small surface of a large lump or cold which they try to penetrate, but can spread over the vast area made by the surface of the fine particles to which the root hairs become so firmly attached.          

            Movement of Water in the Soil. Water passes down the cracks in clay soil and through the pore  spaces in sands and silts. It has been found that if the water-level was 12 inches below the surface the growth of grass was good, but was poor when the water was at 20 inches depth and that  the grass failed when water was 26 inches below. A clay  soil may be seen cracking with drought when only a few feet away from a stream.

            Formerly it was thought that the rise and movement  of water was brought about by capillarity, by the agency of thin films of water, and the transfer of water from thick films at lower depths to the thin films near the surface where water had been lost by evaporation. It was considered  that water could rise in this way several feet.

            While it is still true that capillarity the down-ward flow of water by gravity, it is not sufficient to bring  the water to the surface nor to distribute the water.

            The supply of water to the plant  depends on the rainfall and on the absorbing and retaining  power of the soil. The value of humus or organic matter for this purpose will therefore be realized.

            Physical properties of the soils. Soils are classified and mapped generally on the basis of physical characteristics which the surveyors  can recognize by visual inspection. Many of the important chemical and biological properties are reflected by the physical properties of the soil. Further more, the physical properties of soils determine  to a large  extent their  productive capacity. The aeration and moisture  relations, as well as area of root penetration, are  determined largely by the physical makeup of soils profile.

 

 

 

           

References

1.      Muller, Franz. Agrochemicals: Composition, Production, Toxicology, Applications. New York: VCH Publishing, 2000.

2.      Plimmer, Jack R. Encyclopedia of Agrochemicals. New York: John Wiley & Sons, 2002.

3.      Spearks, Donald L. Environmental Soil Chemistry. 2nd ed. New York: Academic Press, 2002.

4.      Soil Microbiology, ecology and biochemistry in perspective.  E.A. Paul    2007.

5.      Ïîñîáèå ïî àíãëèéñêîìó ÿçûêó äëÿ ñåëüñêîõîçÿéñòâåííûõ òåõíèêóìîâ Ìîñêâà 1979.

6.      Àíãëèéñêèé ÿçûê : ýêîëîãèÿ è îõðàíà îêðóæàþùåé ñðåäû. Î.À. Ïèñüìåííàÿ Ìîñêâà 2007.

7.      Modern Agriculture  Moscow 1972.