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the basic procedure for the mechanical working of soil with moldboard plows. In plowing, there is the simultaneous turning over, loosening, and intermingling of the soil. Turning over the soil buries the sod, fertilizers, weed seeds, many agricultural pests, and the causative agents of diseases. In the lower portion of the topsoil that is brought to the surface by plowing, the content of nutrients accessible for the plants increases under the effect of aeration, repeated moistening, and the rapidly activating useful soil microflora. Plowing makes it possible to maintain a small-clot composition of the topsoil. The degree of turning depends upon the shape of the moldboards and the ratio of the depth of working to the width of the furrow. Plows with helical moldboards (used on heavy clay and heavily grassed earths) turn the furrow most completely but break up the soil little. With cylindrical moldboards, the soil is broken up well, but the furrow is not turned over satisfactorily. With a cultivation form of the moldboard, the furrow is turned over well and broken up on soils of medium cohesiveness (with skim-colters and on grassed soils).
There are three forms of plowing: furrow slice inversion, breaking, and cultivation plowing. In furrow slice inversion, the soil is plowed in a slice up to 40 cm wide, with relatively shallow plowing with a helical moldboard and with the soil being turned 180°. This is the oldest type of plowing sod. Numerous additional tillings are required (harrowing, cultivation, discing, and rolling), which lead to the excessive pulverizing of the soil. The term “furrow slice inversion” in agricultural production can also mean the second plowing of virgin land, fallow land, or a field of perennial grasses. In breaking, or first plowing, the furrow slices are turned 135° by moldboards of the semihelical type; the slices lie closely to one another and lie at a 45° angle to the soil surface. With the breaking of virgin land or fallow, the sod does not break down for several months. Such plowing cannot be used on long-plowed lands, and in addition it requires repeated discing and harrowing. Cultivation plowing is carried out with a plow, each body of which has a skim-colter. The skim-colter cuts the surface soil layer and rolls it to the bottom of the furrow. The moldboard of the basic plow body raises a rigid soil layer, with which it covers the upper layer that has been turned to the bottom. This is the most modern type of plowing. The surface of the plowed field is even, which facilitates the subsequent presowing tilling (the skim-colter is taken off only in plowing manure under or in replowing a fallow field).
The depth of plowing is set depending upon the thickness of the plow layer, the biological features of the plants being raised, the working of the soil for the preceding crops, the degree and character of field weediness, and the presence of pests and diseases of agricultural plants. Plowing to a depth of 20 cm is considered normal; to a greater depth it is called deep plowing, and to a lesser depth, shallow plowing. Plowing at the same depth will often lead to the formation of a compacted layer (the plow pan) on the bottom of the furrow, which disrupts a normal water regime in the soil and impedes the development of the plant root system. For this reason, it is expedient periodically to plow somewhat deeper than usual in each field of the rotation. Deep plowing is one of the most important conditions for obtaining high and stable yields. On soils with a plow layer of less than 20 cm, which limits the depth of plowing, a thick cultivated plow layer is gradually created. Here, as with the case of deep plowing, plowing with a subsoil plow that loosens the soil horizon can make a significant difference.
The time of plowing depends upon the zonal soil and climatic features, the farming methods for the crops being raised, the sowing time, and a number of other conditions. The most modern method is early fall plowing, which helps to improve moisture and nutrient accumulation in the soil in a form accessible for the plants. Summer plowing is essential in preparing occupied fallow for planting and in sowing winter crops on nonfallow land that has already been cropped. Plowing for spring crops of the same sowing year is known as spring plowing. The spring and summer plowing, and some-times the autumn plowings, should be accompanied simultaneously by harrowing (for reducing moisture losses from evaporation).
Plowing-in land (strip plowing) is the most widespread method of plowing. The field is divided up beforehand into individual long areas or strips, the length of which is determined by the size, configuration, and relief of the field. The width of the strip should be a multiple of the width of the working reach of the unit, and it should be uniform along the entire length. At the ends of the strips, turning areas are struck off. The plowing is done inside-out and outside-in. Inside-out plowing is begun in the middle of the strip. The unit, having made the first pass, makes a noncutting turn to the right, and the second furrow is made next to the first. In resting against one another, the slices form a crest. Subsequently the unit turns thus only to the right; it ends the plowing at the edges of the strip, where one furrow is formed. Outside-in plowing, on the contrary, is begun at the edges of the strip. In making the first pass, the unit turns to the left, and then makes the second pass on the other edge of the strip, and so forth. In this instance, the furrow is in the middle of the strip, and the crests are along its edges. There is also the method of smooth plowing, where there is no need to stake out turning strips. This plowing is done using swivel plows with a double set of bodies (the furrow slices are laid down only to one side). On the plowed land, separate furrows and heaped-up crests are not formed. This method of plowing is usually used on areas with a significant incline. There is also figure plowing (round plowing), with which there inevitably are lapses, a poor quality of tilling, and excessive compacting of the soil with the turning of the unit.
The direction of the plowing can also be of great agronomical significance. If it is essential to retain the courses of thaw and rainwater and to prevent the washing away of the soil, then it is advisable to plow across the slopes. Situations of light soils and strong winds call for plowing perpendicular to the direction of the prevailing winds. In the spring and summer seasons this weakens the winnowing of the topsoil, and during the winter it helps to retain snow on the fields. In each specific instance, the direction of plowing should be determined by the farm agronomist, considering not only the terrain but also the procedures of subsequent farm work on the given field.
The quality of plowing depends upon the technical properties of the soil, that is, on its coherence, plasticity, and adhesiveness to the working parts of the plow. These properties are determined chiefly by the mechanical composition of the soil. In plowing clayish and loamy soils, the degree of their moistness must also be considered. In plowing heavy unstructured soils, it is essential not to delay for even several hours; the work must be started as soon as the soil acquires a state of mellowness. Among the basic indicators for the quality of plowing are depth, the presence of lapses, ridginess, the degree of breaking up, dumpiness, and the straightness of the furrows. Plantation and stage plowing are other varieties of plowing.
Under certain soil-climatic and farming conditions, it is often advisable to use moldboardless cultivation instead of plowing.
REFERENCEZemledelie. Edited by S. A. Vorob’ev. Moscow, 1968. Pages 204-14.
L. N. BARSUKOV
a method of narrow-web coal mining in which the bed is broken and the coal loaded onto a face conveyor by a coal plow. Plowing is usually used in extracting soft coals and coals of medium hardness in gently sloping (up to 25°) seams, usually 0.5–2.0 m thick; in some cases, it may be used for steep seams up to 1.2 m thick. Roof control is achieved during plowing by caving in or walling up the area that has already been worked. In order to make plowing more efficient, the coal body may be weakened ahead of time by forcing water into the seam at pressures up to 30 meganewtons per m2 (300 standard atmospheres) through blast-holes or boreholes. When the coal has been moistened, dust formation is also lessened.
The chief advantages of the plowing method are an improvement in the grade of the coals and anthracites extracted, reduced dust formation during mining, the possibility of excavating seams where there is a danger of a sudden release of coal and gas, and the relative simplicity and reliability of the equipment used.
Plowing is most common in the Federal Republic of Germany, the Netherlands, and Belgium. In the USSR it accounts for approximately 4 percent of underground coal mining. As of 1976, plowing was being used to a significantly greater extent, particularly for working very thin, sloping seams.
V. N. KHORIN