Tillage implements
How ploughs, harrows, cultivators, rotavators and subsoilers work, mouldboard plough parts, disc and tine tools, with draft and bite length sums.
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A tillage implement is a tool for applying force to soil in a particular way: cutting, lifting, inverting, breaking, mixing or firming it. The shape of each tool, mouldboard, disc, tine or blade, determines what it does to the soil, how much power it needs, and which soils and conditions it suits. Knowing how implements are built and adjusted helps farmers get a good seedbed with less fuel, less soil damage and less wear.
Tillage implements, their parts and their adjustment are standard practical topics in farm machinery courses. The purposes of tillage and the choice between conventional, conservation and zero tillage are covered in a separate article on tillage.
Primary tillage implements
Mouldboard plough
The classic inversion plough. Each bottom has:
- Share: the cutting edge that slices the furrow horizontally; it wears fastest and is replaceable.
- Mouldboard: the curved surface that lifts, turns and inverts the furrow slice. General-purpose mouldboards suit most soils; stubble types with a short, steep curve break the slice more; sod (breaker) types with a long, gentle twist turn grassland cleanly; slatted mouldboards reduce soil sticking.
- Landside: bears against the furrow wall to resist side thrust and keep the plough straight.
- Frog: the frame to which share, mouldboard and landside are bolted.
- Coulter (disc or knife) ahead of the bottom cuts the slice vertically and residues.
Adjustments include suction (vertical and horizontal clearance of the share point, which helps the plough enter the soil and hold width), width of cut, depth, and levelling. Reversible ploughs carry left- and right-hand bottoms so all furrows can be turned the same way.
Disc plough
Large concave discs, tilted and angled to the direction of travel, roll through the soil, cutting and partly inverting it. They suit hard, dry, sticky, stony or root-filled soils where a mouldboard would be damaged or would not scour, but leave a rougher finish.
Chisel plough and subsoiler
- Chisel ploughs have rigid or spring-loaded tines with narrow points that shatter and loosen soil to 20 to 40 cm without inverting it, leaving residue on the surface.
- Subsoilers (rippers) are heavy single tines, sometimes with winged points, pulled 40 cm or deeper to break compacted layers and plough pans, best when the subsoil is dry enough to shatter.
Rotary tiller (rotavator)
A PTO-driven rotor carries L-shaped or C-shaped blades that chop and mix soil and residue. It can produce a seedbed in one or two passes and works well in wet rice fields (puddling), but uses much power per unit of soil worked and can destroy structure and form a pan if overused.
Secondary tillage implements
- Disc harrows: gangs of smaller discs; single-action, tandem (two pairs of gangs throwing soil in opposite directions, leaving the field level) and offset (heavy, one front and one rear gang) types break clods and cut residues.
- Tine (spring or rigid) harrows and cultivators: tines with sweeps, shovels or duck-foot points stir the soil, kill small weeds and prepare the seedbed; also used between crop rows.
- Rollers and packers (smooth, ridged or ring rollers) crush clods and firm the seedbed.
- Levellers, planks and land planes, including laser levellers, smooth the field for even irrigation.
- Ridgers and bed formers make ridges, furrows and raised beds.
Matching implement to soil and power
Draft depends on soil type and moisture, depth, width, speed and the implement's design. As a guide, typical specific draft values for mouldboard ploughs range from about 20 to 50 kN per m2 of furrow cross-section in sandy and loam soils, to 70 kN per m2 or more in heavy clays. Implements must be matched to the tractor's drawbar or PTO power, and set up to work at the right depth with minimal side draft.
Plough draft and rotavator bite length
Plough draft. A three-bottom mouldboard plough cuts 30 cm per bottom at 20 cm depth in a loam with a specific draft of 60 kN per m2.
- Furrow area per bottom = 0.30 × 0.20 = 0.06 m2; total = 0.18 m2.
- Draft = 60 × 0.18 = 10.8 kN.
- At 5 km/h (1.39 m/s), drawbar power = 10.8 × 1.39 ≈ 15 kW. On tilled soil, where drawbar power is about two-thirds of PTO power, the tractor needs at least about 22 kW at the PTO, plus a margin.
Rotavator bite length. The bite length, the length of soil slice cut by each blade, controls how fine the tilth is:
Bite length (m) = forward speed (m/s) × 60 ÷ (rotor speed in rpm × number of blades per flange cutting in the same plane)
- Forward speed 3 km/h = 0.833 m/s; rotor 200 rpm; 3 blades per flange.
- Bite length = 0.833 × 60 ÷ (200 × 3) ≈ 0.083 m (8.3 cm).
Driving faster or slowing the rotor makes bites longer and the tilth coarser; slower travel or faster rotation gives a finer, more powdery seedbed but uses more fuel and harms structure.
Care and maintenance
- Replace or sharpen worn shares, points and blades; worn shares increase draft and reduce penetration.
- Keep mouldboards polished so soil slides off (scouring).
- Check bearings on discs and rotors, and tighten bolts.
- Store implements clean, greased and under cover.
Key points
- Primary tillage: mouldboard, disc and chisel ploughs, subsoilers and rotary tillers; secondary tillage: disc and tine harrows, cultivators, rollers, levellers and ridgers.
- Mouldboard bottom parts: share, mouldboard, landside, frog, and coulter ahead.
- Disc ploughs suit hard, sticky, stony soils; chisels and subsoilers loosen without inversion; rotavators chop and mix with high power use.
- Draft = specific draft × furrow area; drawbar power = draft × speed.
- Rotavator bite length = speed × 60 ÷ (rpm × blades per flange).
What the exams ask
- School-leaving and entrance papers: names and uses of primary and secondary tillage implements.
- Degree and research-fellowship entrances: parts of the mouldboard plough, types of mouldboards, disc plough versus disc harrow, suction and adjustments, and rotavator blades.
- Agricultural engineering examinations: draft and power calculations, bite length, implement–tractor matching, and design of tillage tools.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
What is suction in a plough?
The small downward and sideways clearance of the share point relative to the landside. It helps the plough bite into the soil and hold its depth and width. Worn shares lose suction and ride out of the ground.
Why does a disc plough suit stony soil?
Its discs roll over obstacles instead of catching them, so they are less likely to break, and they cut through roots and hard soil that would stop a mouldboard.
Is a rotavator bad for soil?
Used occasionally and at the right moisture, it prepares a fine seedbed quickly. Repeated, high-speed rotavation pulverises aggregates, forms pans and speeds loss of organic matter.
Sources
- Kepner, R. A., Bainer, R. and Barger, E. L. Principles of Farm Machinery, 3rd edition. AVI Publishing, 1978.
- Srivastava, A. K., Goering, C. E., Rohrbach, R. P. and Buckmaster, D. R. Engineering Principles of Agricultural Machines, 2nd edition. ASABE, 2006.
- ASABE. Agricultural Machinery Management Data (ASAE D497). American Society of Agricultural and Biological Engineers.
- Hunt, D. and Wilson, D. Farm Power and Machinery Management, 11th edition. Waveland Press, 2016.
- Bernacki, H., Haman, J. and Kanafojski, C. Agricultural Machines: Theory and Construction, volume 1. US Department of Commerce translation, 1972.
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