an agricultural machine for shallow cultivation of soil and the care of plants. The earliest known use of the harrow is during Roman times (Italy, first century B.C.). It was widely used among Slavic tribes no later than the end of the first millennium A.D. The first written mention of the harrow is contained in Russkaia pravda (11th—12th centuries). The most ancient form of harrow in Rus’ was the sukovatka—the trunk of a fir tree with the branches cut off to a length of 50–70 cm. The types of harrows used later included bow harrows, made of bound trimmings of tree trunks with branches 35–50 cm long; wattled harrows, consisting of a number of wooden beams and stakes tied with bast fiber; harrows with wooden frames and metal teeth and also with metal frames and metal teeth; and disk harrows. All these harrows were drawn through the fields by draft animals. As a rule, present-day harrows have metal frames and metal working parts. They are usually coupled to tractors.
Present-day harrows are divided into toothed and disk types and into types for general and specific use.
Toothed harrows are used for cultivation of the top layer of the soil after plowing, for breaking up the soil crust in the spring on plantings of winter crops and for harrowing seedlings, for embedding seeds and applying mineral fertilizers, for leveling fields before sowing, and for destroying weeds. The working parts of these harrows are steel teeth (square, round, rectangular, or knifelike). The teeth are attached rigidly or hinged to the frame or to a spring base. A zigzag frame has been adopted for toothed harrows, which ensures symmetrical placement of teeth and less jamming of equipment. These harrows are divided, according to the load capacity of each tooth, into heavy (16–20 newtons [N]), medium (12–16 N), and light (5–12 N; 1 N ≈ 0.1 kg force).
Types of toothed harrows include the “Zigzag,” smoothing, latticed, spring-tooth, weeding, grassland, and rotary-knife. The Zigzag consists of three toothed units; they are produced either as trailers or tractor-mounted. A smoothing harrow consists of two units. Each unit has a steel blade (grader), a harrow with one row of teeth, and a rake of four bars. The grader shears off ridges and clods, the teeth crumble them, and the bars of the rake pulverize clumps and level the surface of the field. The latticed harrow has teeth of circular steel that are hinged and form a latticework that adapts well to irregularities of the field. Latticed harrows may be trailers or tractor-mounted. The latticed thinning harrow (currycomb) is designed for thinning shoots of sugar beets and for weeding sugar beets and corn. The harrow consists of two sections with irregularly bent links ending in teeth. The spring-tooth harrow consists of three bars with attached spring teeth. The weeding harrow has elastic spring teeth with sharp ends, which are used to simultaneously cultivate the protective zones around plants and the space between rows. The meadow harrow is equipped with platelike, scraper-type blades that break up clumps of earth, level molehills, comb out rotted roots of herbs, and so on. The rotary-knife harrow is designed for work on soils littered with stones. Its working parts are platelike blades attached to rotating shafts. The harrow adapts well to irregularities in the field and overrides obstructions (stumps and stones) up to 35 cm high. The characteristic features of toothed harrows made in the USSR are presented in Table 1.
Disk harrows are used mainly for the cultivation of grass-covered layers and for breaking up large clods and clumps of soil. Their working parts are smooth or serrated disks 450, 510, or 660 mm in diameter. The disks are mounted in gangs.
| Table 1. Characteristics of toothed harrows | |||||
|---|---|---|---|---|---|
| Type | Modal | Working width (m) | Depth ot cultivation (m) | Weight (kg) | Productivity (ha/hr) |
| Heavy | ZBZTU-1.0 | 2.8 | 5–6 | 140 | 2.0 |
| Medium | ZBZS-1.0 | 2.9 | 5–6 | 100 | 2.0 |
| Seeding | ZBP-1.0 | 1.8 | 5–6 | 47 | 1.4 |
| Smoothing | ShB-2.5 | 25 | 3–5 | 110 | 0.9–1.0 |
| Latticed | BS-2.0 | 2.0 | up to 6 | 96 | 1.3 |
| BSO-4.0 | 4.0 | 4–8 | 93 | 2.6 | |
| BSP-4.0 | 4.0 | 4 | 140 | 1.15 | |
| Spring-tooth | PB-9A | 0.9 | up to 10 | 68 | 0.37 |
| Meadow | BLSh-2.3 | 2.3 | — | 260 | 1.8 |
| Pasture | BPSh-3.1 | 3.1 | — | 202 | 2.2 |
| Rotary-blade | BNV-3.0 | 3.0 | up to 10 | 320 | 1.5 |
| With palmate teeth | ZBZL-1.0 | 3.0 | 4–6 | 260 | 1.8 |
| Table 2. Characteristics of disk harrows | |||||||
|---|---|---|---|---|---|---|---|
| Type | Model | Working Width | Depth ol cultivation (cm) | Weight (kg) | Disk diameter(mm) | Productivity (ha/hr) | |
| Swamp | |||||||
| Tractor-mounted | BDT-2.5A | 2.5 | 25 | 1,600 | 660 | 1.2–1.4 | |
| Trailer | BDNT-2.2 | 2.2 | 20 | 850 | 660 | 1.0 | |
| Field | |||||||
| Tractor-mounted | BD-4.1 | 4.1 | 9 | 1,270 | 510 | 3.4 | |
| Semitrailer | BDP-4.1 | 4.1 | 12 | 1,180 | 510 | 2.5 | |
| Trailer | BDN-2.0 | 2.0 | 12 | 425 | 445 | 1.0 | |
| Orchard | |||||||
| Semitrailer | BDN-2.2M | 2.2 | 11 | 665 | 510 | 1.2 | |
| Trailer | BDN-1.3 | 1.3 | 10 | 315 | 450 | 1.1 | |
The disks, which are placed at an angle to the direction of the machine’s movement and rotate as they work, cut the layers of soil, crumble it, turn it over, and push it aside. Disk harrows are divided into swamp, field, and orchard types, trailers, semitrailers, and tractor-mounted. Field harrows have gangs equipped with ballast bins to which weights are added, increasing the weight of the harrow with a view to better cultivation of the soil. The gangs of orchard harrows for working the soil between rows and around tree trunks and berry bushes are placed asymmetrically in relation to the longitudinal axis of the harrow, as a result of which the point of attachment is shifted to one side, making it possible to remove the tractor to a distance of 1.5–3.5 m from fruit trees. In addition, the harrows are equipped with a device for diverting the gangs to the space between rows when they touch a fruit tree. The characteristic feature of disk harrows made in the USSR are presented in Table 2.
I. M. PANOV