Primary tillage

Types of plowing

Due to the wide diversity of natural-climatic zones and soil properties, there are various types of plowing; the correct choice determines soil fertility and yield.

Types of plowing:

I — with complete turning of the furrow slice; II — with the furrow slice thrown up; III — with a corner cutter; IV — cultural; V — two-tier; VI — diamond-shaped; VII — non-moldboard; VIII — cultural with a subsoiler; IX — with cutaway plow bodies; X — three-tier. 1 — part of the podzolic layer; 2 — part of the podzolic layer mixed with the cultivated layer; 3 — cultivated layer before plowing; 4 — inclusions of the podzolic layer; 5 — upper cultivated layer; 6 — middle podzolized layer; 7 — lower illuvial layer.

The most common types of plowing are shown in the figure (the cross-section of the furrow slices is shown without taking their deformation into account).

Plowing with complete turning of the furrow slice (Fig. I) is the oldest type of tillage, used in the development of steppe virgin lands. The main task when plowing virgin land is to destroy the vegetation cover and deprive it of vital activity. Plowing with complete turning of the slice achieves these goals, since vegetation buried at the bottom of the furrow is completely deprived of sunlight and dies. Complete turning of the slice is achieved by using working parts with helical surfaces, provided that the slice width b ≥ 2a, where a is its thickness.

Throwing up the furrow slice (Fig. II) began to be used almost two centuries ago for the tillage of cohesive sodded soils. Based on the theory of mineral plant nutrition, the main task of this type of plowing is to provide the greatest arable surface for maximum exposure of the soil to air, heat and light. This type of tillage is obtained when using helical working surfaces, when the slice width b < 2a. When plowing with the slice thrown up, voids (sinuses) form, which disrupt the soil water-air regime, leading to rapid drying. The field becomes ridged, and the viability of the sod is not fully suppressed. At the joints of the slices, unburied sod protrudes; in the depths of the formed furrows, rainwater accumulates, promoting sod regrowth. To eliminate this drawback with a corner cutter, a small three-sided soil slice is cut from the field side and dropped to the bottom of the furrow (Fig. III). As a result, sod is absent at the joints of the slices, and the slice cut by the corner cutter and dropped to the bottom of the furrow covers the joint from below, hindering sod regrowth and its emergence to the surface.

Cultural plowing, or plowing with cylindrical (cultural) working surfaces and skim coulters (Fig. IV), is used for the tillage of light old-arable soils, which during tillage with plows having helical working surfaces do not form a slice but crumble into structural aggregates. The skim coulter or sod cutter (jointer) cuts a four-sided soil prism from the slice and drops it to the bottom of the furrow. At the same time, the main slice, being freed from most of the sod, crumbles better and more completely incorporates plant residues.

The working width of the skim coulter is 2/3 of the working width of the main plow body. If its working width is set equal to b, two-tier plowing is obtained (Fig. V). Two-tier plowing is used for soil tillage under crops requiring increased tillage depth (for example, sugar beet, cotton).

Diamond-shaped plowing got its name from the shape of the cross-section of the slice, resembling a rhombus (Fig. VI). The rhomboid cross-section of the slice is formed by cutting the soil with two shares: one from the side of the furrow bottom, the other from the side of the furrow wall. The latter is made in the form of part of a spherical disk. Diamond-shaped plowing allows a wide open furrow in which the right tractor wheels roll freely. The disadvantages of this type of soil tillage are the high specific material consumption of technical means (1.45–1.9 times higher), insufficiently complete incorporation of plant residues (58–97%), and the possibility of sod emerging to the day surface at the joints of the slices.

Non-moldboard plowing (Fig. VII) is carried out periodically, usually once every 4–5 years, in zones of insufficient moisture, on soils subject to wind erosion and on slopes. It is performed by plow bodies without moldboards. Non-moldboard plowing is a type of deep loosening. The main task is to increase soil water permeability and maximize moisture conservation.

Plowing with a subsoiler (Fig. VIII) is used on sod-podzolic soils with a relatively shallow podzolic layer (podzol). Since bringing podzol to the surface reduces soil fertility, cultural plowing with turning of the slice is carried out to a depth equal to the thickness of the cultivated layer. The podzolic layer is only loosened by subsoilers; as a result, soil-forming processes begin in it and after several years it becomes fertile.

Plowing with plows with cutaway bodies (Fig. IX) is used on sod-podzolic soils. The podzolic layer crumbled by the share passes through the cutout of the moldboard and remains at the bottom of the furrow; the cultivated layer goes onto the moldboard, turns over, crumbles and covers the loosened podzolic layer. Thus, only a small part of the podzolic layer, rising along the bridge between the share and the moldboard, mixes with the cultivated layer, forming inclusions. The resulting soil-forming process leads to the cultivation of the inclusions and an increase in the thickness of the layer.

Three-tier soil tillage (Fig. X) is used on solonetzic and podzolic soils. In columnar solonetzes and podzols, three genetic horizons often stand out: the upper humus fertile layer (marked 5 in the figure), the middle solonetzic or podzolized infertile and even harmful layer for plants (6 in the figure), and the lower carbonate or illuvial layer rich in gypsum, lime and calcium (7 in the figure). Of the three different methods of soil tillage proposed by different authors, the most widespread is the method of Academician V. P. Mosolov. It is based on the use of lime, gypsum and calcium contained in the lower carbonate or illuvial soil layer. According to this most economical method of reclamation, the upper fertile layer 5 is turned and loosened but remains in place; the middle infertile solonetzic or podzolized layer 6 moves down, and its place is occupied by the lower carbonate or illuvial layer.

Smooth plowing — plowing without backfurrows and dead furrows, carried out with plows intended for smooth plowing: reversible, frontal, shuttle, turnable, key and balance plows. The plowed field has a leveled surface, thereby providing more favorable conditions for plant growth and for the operation of machines performing subsequent technological operations. The yield of cultivated plants under smooth plowing increases by 5–10%, machine productivity by 10–15%; in addition, harvesting losses are reduced.

In addition to the listed types of plowing, under some conditions special types of soil tillage are used, for example, on slopes stepped, combined and combined-stepped tillage. In stepped plowing, the plow bodies, alternating every other one, have elongated standards and, consequently, till deeper, forming a stepped furrow bottom. In combined plowing, non-moldboard and moldboard bodies alternate. As a result, along the passes of the non-moldboard bodies stubble remains, and the moldboard bodies bury it, forming ridges. Combined-stepped plowing is a combination of the two listed types. The main task of such types of plowing is to reduce water runoff along the slope, that is, to prevent water soil erosion.

Agrotechnical requirements

Autumn plowing of old-arable lands and primary plowing of virgin lands are performed with share plows with skim coulters. Replowing of fallow and incorporation of manure are carried out without skim coulters. Sodded soils are treated with turning, but without loosening the slice (other implements are used for loosening).

Plowing depth is determined by zonal features, the thickness of the arable layer and soil type, crop characteristics, as well as the depth of primary tillage under preceding crops and weed infestation.

Depending on the depth, plowing is divided into:

• shallow — less than 20 cm,
• normal — 20–23 cm,
• deep — 24–40 cm,
• plantation — more than 40 cm.

Soil tillage depth is determined by the requirements of the cultivated crop, the structure and thickness of the arable layer and other factors. For most crops, the optimal plowing depth is 20–22 cm. Soils with an insufficient arable layer are plowed to its full depth, gradually increasing it with subsoilers, for example, for sod-podzolic soils by 4–5 cm annually. Sod-podzolic soils are usually tilled to a depth of 20–22 cm, well-cultivated and gray forest soils to a depth of up to 26–28 cm, and chernozem soils under row crops are plowed to a depth of up to 28–32 cm.

On fields with a fertile layer thickness of less than 20 cm, plowing is carried out to a depth equal to the thickness of the fertile layer, and the subarable layer is simultaneously treated with subsoilers to break the plow sole and gradually increase the thickness of the fertile layer.

As a result of annual plowing, the plow sole becomes compacted. To break it, the plowing depth is periodically increased to 25–27 cm or loosening with chisel plows is carried out.

Plowing dates depend on soil-climatic conditions, soil moisture and the cultivated crop. Autumn tillage for spring crops is carried out after harvesting the predecessors; spring plowing is performed at physical ripeness: for clay soils — 50–65% of minimum moisture capacity, for loamy soils — 40–70%. More moist soils crumble worse, stick to wheels and working parts, as a result of which the traction resistance of the plow and energy costs for plowing increase. For winter crops — 2–3 weeks before sowing.

On stony soils, plows with safety devices are used; a corner cutter is installed on the plow bodies, cutting off the corner of the slice during its movement along the moldboard.

For intensive crumbling of the soil slice, plowing can be combined with additional treatment by attachments TMCR-2.3 and TMCR-3.5, hitched to the plow. When soil moisture is more than 70%, instead of these attachments, tooth harrows are attached to the plow.

Plowing speed should correspond to the speed established for the used bodies: 1.4–2.2 m/s for conventional and 2.2–3.3 m/s for high-speed.

Determining the plowing direction

The direction and method of movement of the unit depend on the size, configuration of the field, length of the run, slope and other conditions.

Plowing along the long side of the field is more productive than along the short side. For fields wider than 300 m, it is recommended to change the plowing direction annually, which improves the soil condition.

On simple slopes, plowing is carried out perpendicular to the slope runoff, that is, across the slope or along the contour. On complex slopes — along contours, the so-called contour plowing. On leveled fields, it is done in the direction perpendicular to the previous plowing. Under wind erosion risk — perpendicular to the prevailing winds. Under excessive moisture with a slope of up to 1–2°, field plowing is carried out along the slope; with a greater slope, for more uniform runoff of excess water — diagonally across the field.

On slopes, plowing is recommended with reversible or shuttle plows.

When plowing with frontal plows, division into plots is not required, since movement is carried out in a shuttle manner.

Plots

Before tillage, the field is divided into plots (areas) with parallel sides, ensuring straight-line movement of the unit. The strip of the first pass is marked with pegs (stakes) installed 50–80 m apart.

Determining the optimal width of plots depending on the length of the plot and tractor power.

The width of the plot depends on the length of the run, the method of movement of the unit and the number of plow bodies. For this, reference data or a graph are used.

Sizes of headlands for turning units:

• for tractors MTZ-80, MTZ-82 with a three-body plow — 0–12 m;
• for DT-75, T-74 with a four-body plow — 12–15 m;
• for T-150K, K-701 — 24–30 m.

Making a backfurrow:

A — in two passes of the unit, B — in three passes of the unit, a — position of the plow and soil during the first pass, b — position of the plow and soil during the second pass.

On all odd plots, plowing of the backfurrow is performed. As a rule, it is done by backfurrow plowing in three passes. During the first pass, the plow is adjusted so that the first body moves on the soil surface and the last plows to the specified depth. During the second pass, all plow bodies are set to the specified depth and guided so that the first body follows the track of the penultimate one, partially covering the open furrow from the first pass. During the third pass, a low backfurrow is formed in accordance with the requirements.

For better leveling of the field, plots are recommended to be plowed alternately in backfurrow and dead furrow. The backfurrow should be straight, and the plowing depth under it should be not less than half the specified depth; its height should not exceed 10 cm.

The highest quality of plowing is obtained in four passes of the unit: after the first two passes (dead furrow), at the place of the future backfurrow, a dead furrow is formed with a width equal to twice the working width of the plow body; the third and fourth passes are performed in the reverse direction respectively along the second and first passes. As a result, a relatively level field surface is obtained. The dead furrow should be straight and equal to the working width of the plow body.

For laying the first furrows and backfurrow plowing the boundaries of headlands, the first passes of the unit must be performed by backfurrow plowing in three passes or dead furrow plowing in four passes of the unit. The plow for the first pass of backfurrow plowing is set so that the first body slides on the field surface and the last plows to the specified depth. The second pass is performed so that the first body, set to the specified plowing depth, follows the track of the penultimate body. The third pass is performed as in ordinary plowing. For the first and second passes of dead furrow plowing, the plow is adjusted so that the first body slides on the field surface and the last is buried to half the specified plowing depth. After that, all plow bodies are adjusted to the specified tillage depth and the third and fourth passes are made, directing the first body along the track of the penultimate body respectively during the second and first passes. This fills the dead furrow and forms a small backfurrow.

After plowing all plots, the headlands are treated in dead furrow and the split furrows are filled. For filling furrows, the plow is adjusted so that the first body plows to the specified depth or 5–6 cm deeper and moves next to the open furrow, while the rear body slides on the field surface.

Methods of unit movement

Scheme of plot loop plowing with alternation of plots in backfurrow and dead furrow:

I-IV — plot numbers, 1-8 — pass numbers, C — width of plots.

When plowing a field, the following methods of unit movement are most often used:

• loop with alternation of plots in backfurrow and dead furrow;
• combined loopless;
• non-plot circular.

With the loop method, regardless of the number of plots on the field, odd plots are plowed in backfurrow, even plots in dead furrow, or vice versa. When starting treatment from the middle of the plot, a backfurrow forms in its center, and furrows at the edges. Conversely, when starting plowing from the edges, a dead furrow forms in the middle of the plot. By alternating plots in backfurrow and dead furrow, the number of backfurrows and dead furrows on the field decreases.

With a short run length, the combined loopless method of movement is used, in which the first plot is plowed in dead furrow until loopless turning is possible; the remaining part of the plot is plowed together with the nearby plot.

On leveled fields of rectangular or square shape with an area of not less than 50 ha, the non-plot circular method is used. Plowing with this method is done in circles, starting from the middle of the field to the periphery and vice versa. In the center of the field, a plot in backfurrow is marked out. Then, with a plot width of 30–40 m, it is plowed in circles with a left turn at the corners.

Scheme of movement of the tillage unit with the non-plot circular method from the center to the edge (a) and from the edge to the center (b):

L — length of the area, B — width.

The non-plot circular method allows ensuring a leveled field surface without backfurrows and dead furrows, increasing unit productivity and reducing fuel consumption. The limitation of this method is the complexity of dividing the field and uneven wear of machinery with constant left turning.