Agricultural Engineering · Farm Machinery & Power · also Farm Machinery & Equipment-I, Tillage and Planting Machinery
Machines that prepare the seedbed and put seed and fertiliser in the ground, and how to calibrate and cost them.
In the exams: GATE AG Section 2 Farm Machinery (~11 marks a year 2019–26; seed-drill calibration in 7 of 8 papers); ICAR AIEEA-PG Unit V; ICAR AICE subject 39 Unit 1; PRC ABE; state PSCs
This subject covers the machines that prepare a seedbed and place seed, seedlings and fertiliser in the soil: ploughs, harrows, cultivators and rotary tillers; seed drills, planters and transplanters; and fertiliser distributors. It also covers the arithmetic that decides whether a machine is doing its job and whether it pays: the draft a tool needs, the seed rate a drill delivers, the area a machine covers in an hour, and what each hectare costs. Tillage is usually the most energy-hungry field operation on an arable farm, and sowing is the operation where a mistake costs the most, because a bad stand cannot be corrected later in the season.
The same machines are built and taught very differently around the world. A smallholder in Bihar or Nepal may use an animal-drawn plough, a two-wheel tractor with a rotary tiller and a manual paddy transplanter; a grain farm in Saskatchewan or Western Australia uses a no-till air seeder more than 15 m wide; a Dutch vegetable grower uses a plug-tray transplanter. The physics is the same in all of them: soil fails under a tool in predictable ways, seed metering depends on the geometry of a cell or flute, and field capacity is width times speed times efficiency. This manual teaches the physics first and then says where practice differs by country, soil or crop.
Examiners worldwide lean on a small set of skills. India's GATE Agricultural Engineering paper has asked seed-drill or planter calibration in many recent papers, along with rotary-tiller bite length, plough draft and machinery cost. ICAR's postgraduate and PhD entrance tests and the ASRB NET ask the same content at more depth, including soil-tool mechanics and design. The Philippine ABE licensure and the US NCEES PE Agricultural and Biological exam test power requirements, field capacity and machinery cost using standards such as ASABE D497 and EP496. State public service commissions add local implements and subsidy schemes. Learn the calculations until they are automatic, and learn the reasons behind each machine's shape well enough to explain them to a farmer.
Tillage is the mechanical manipulation of soil to create conditions suited to crop growth. Its classical objectives are to produce a seedbed with enough fine aggregates around the seed for moisture contact while keeping larger clods on the surface against crusting and erosion; to control weeds by burying, cutting or uprooting them; to incorporate crop residue, manure, fertiliser and some soil-applied chemicals; to loosen compacted layers so roots, water and air can move; to shape the surface into beds, ridges or furrows for irrigation and drainage; and, in rice, to puddle the soil. The word tilth describes the physical condition of the soil in relation to plant growth, which depends on aggregate size, porosity, moisture and strength. Every tillage pass costs fuel, labour and time and destroys some soil structure and organic matter, so the modern question is not how much tillage can be done but how little will achieve the objective. Over-tillage leaves a fine, structureless surface that crusts after rain, erodes easily by wind and water, and loses carbon. Tillage at the wrong moisture content, especially when the soil is too wet, smears and compacts the soil instead of loosening it.
Primary tillage is the first, deeper and more aggressive operation after harvest: it cuts and shatters or inverts the soil, typically to 15–30 cm, with a mouldboard plough, disc plough, chisel plough or, for deeper loosening, a subsoiler. It leaves a rough surface. Secondary tillage is shallower and lighter, done after primary tillage to break clods, level the surface, kill weed seedlings and firm the seedbed; implements include disc, spike-tooth and spring-tooth harrows, cultivators, rotary tillers, planks and rollers. Inter-cultivation is tillage between crop rows after emergence, mainly for weeding. Wetland tillage is done in flooded or saturated soil for transplanted rice. Puddling churns the soil with water, destroying aggregates so that fine particles settle into a dense layer. This reduces percolation losses, suppresses weeds, softens the soil for transplanting and helps establish seedlings. The price is poor structure and a compacted plough pan for the crop that follows rice, which is a major concern in rice–wheat systems of South Asia. Puddling is done with cage wheels, rotary tillers and puddlers of various designs.
Conventional tillage means the full sequence of primary and secondary operations common in a region, usually leaving little residue on the surface. Reduced or minimum tillage cuts the number or intensity of passes. Conservation tillage is defined in the United States as any system that leaves at least 30 % of the soil surface covered by residue after planting; this is the threshold used by conservation agencies and is worth remembering. Its forms include no-till or zero-till, where the seed is placed directly into undisturbed soil through residue; strip-till, where only a narrow band in the future row is tilled; ridge-till, where crops are grown on permanent ridges rebuilt each season; and mulch-till, where the whole surface is disturbed but much residue is kept on top. Conservation agriculture, as promoted by FAO, combines three principles: minimum soil disturbance, permanent soil cover and crop diversification. Its benefits are lower erosion, lower fuel and labour use, better water infiltration and timelier sowing. Its challenges are residue handling by the drill, weed control that shifts toward herbicides or cover crops, and slower soil warming in cool climates. In north-west India, zero-till drilling of wheat after rice, and drills that sow into loose or chopped straw, were developed partly to stop burning of rice residue.
The mouldboard plough cuts a furrow slice, lifts it, twists it and inverts it, burying weeds and residue. Its working unit is the bottom. The share is the hardened cutting edge that makes the horizontal cut; its point penetrates, its wing cuts the outer edge of the slice, and the throat joins the share to the mouldboard. The mouldboard is the curved plate that lifts and turns the slice. The landside is a flat plate that presses against the furrow wall and resists the side thrust of the turning slice; its rear end is the heel. The frog is the casting to which share, mouldboard and landside are bolted. The shin is the front, lower edge of the mouldboard above the share point, which makes the vertical cut of the furrow wall. A rolling coulter ahead of the bottom cuts residue and the furrow wall vertically; a jointer turns a small ribbon off the corner of the slice so residue is buried cleanly. The share is set with suction, a small downward bend of the point (vertical suction) and an outward bend of the point toward the land (horizontal suction). Vertical suction pulls the bottom into the ground and horizontal suction holds it to its width of cut; worn shares lose suction and the plough floats out. Share types include the slip share, slip-nose share, shin share and bar-point share. The size of a mouldboard plough is stated as the width of cut of each bottom and the number of bottoms.
Mouldboard shape controls how the slice is handled. A cylindrical, steep, short mouldboard breaks and pulverises the slice and suits stubble in friable soil; the stubble type is of this kind. A helicoidal, long, gently twisted mouldboard lays the slice over with little breaking and suits sod and tough grassland; it is called the sod or breaker type. The general-purpose mouldboard sits between them and is a semi-cylindrical or semi-helicoidal compromise. Slatted mouldboards reduce contact area in sticky soils, and high-speed bottoms have shapes that throw the slice less far at speed. A conventional one-way plough throws all slices to one side, usually the right. Working a field in lands therefore leaves a back furrow, a ridge where two slices are thrown toward each other, and a dead furrow, an open trench where two slices are thrown apart. Gathering starts in the centre of a land and works outward, producing a back furrow; casting starts at the edges and leaves a dead furrow in the centre. A reversible or two-way plough carries left- and right-hand bottoms and flips at each headland, so every slice goes the same way across the field and no back or dead furrows are formed; this is preferred on sloping and irrigated land. The traditional wooden or steel-tipped animal-drawn plough of South Asia and Africa cuts a V-shaped furrow and stirs rather than inverts the soil, so several crossed passes are made.
The furrow slice is the block of soil cut and moved by one bottom; its width is the width of cut and its thickness is the depth of ploughing. The crown is the top of the inverted slice, the furrow wall is the vertical uncut face, and the furrow sole is the bottom of the furrow. A rectangular slice of width b and depth a, turned by a mouldboard, comes to rest leaning at an angle on the previous slice. Classical geometric analysis, found in Bernacki's and Kepner's texts, shows that the slice lies stably only if its centre of gravity falls on the correct side of its lower edge. Setting the lean angle by sin δ = a/b and requiring the centre of gravity to lie over the base gives (a/b)⁴ + (a/b)² ≤ 1, so a/b ≤ 0.786, or b/a ≥ 1.27. If the slice is narrower than about 1.27 times the depth, it tends to fall back into the furrow and residue is poorly buried. For this reason bottoms are designed for a width-to-depth ratio above this limit, and ploughing deeper than a bottom is designed for gives poor inversion. The cross-section of the slice, width times depth, is also the area used to compute unit draft. Plough the correct width: if the front bottom cuts too wide or too narrow, the slices are uneven and the field is left ridged. On a mounted plough, the front furrow width is set by moving the cross-shaft of the linkage, and levelling is done by the top link (fore-and-aft) and the lift rod (sideways).
A disc plough replaces the share and mouldboard with a large, concave, rotating steel disc that cuts, lifts and partly inverts the slice as it rolls. Each disc is set at a disc angle, the horizontal angle between the plane of the disc edge and the direction of travel, and a tilt angle, the angle between the plane of the disc and the vertical. Standard disc ploughs are commonly set with disc angles in the low to mid-40s of degrees and tilt angles of about 15–25°; exact ranges vary with the design, so read the implement manual. Increasing the disc angle widens the cut and aids penetration up to a point; increasing tilt aids inversion but reduces penetration. Because the disc rolls, it rides over roots and stones instead of catching on them, and it wears less in abrasive soils. It works in hard, dry soils where a mouldboard will not penetrate, in sticky soils where a mouldboard will not scour, and in land with roots and stones. It does not rely on suction, so it penetrates by weight: disc ploughs are heavy and often carry added weights. The side thrust on the discs is taken by an angled rear furrow wheel, not by a landside. Scrapers keep the concave face clean in sticky soil. Inversion and burial of residue are less complete than with a mouldboard, and the furrow sole is uneven. Vertical-disc or harrow ploughs carry many smaller discs on one gang shaft and do shallower, faster primary tillage.
A chisel plough has rigid or spring-loaded shanks, each carrying a narrow point, spaced across a frame. It shatters and loosens soil without inverting it, leaving much of the residue on the surface, so it is a standard primary implement in reduced and conservation tillage. Spring-cushioned shanks trip over stones; rigid shanks hold depth in hard ground. Points may be straight chisels for deep shattering or twisted shovels that mix more residue. The chisel plough needs less draft per unit width than a mouldboard plough in many soils and leaves a rough, cloddy surface that resists erosion. Shank spacing and depth must be matched so that the loosened zones meet below the surface; if the shanks are too far apart for the depth, ridges of untilled soil remain between them. Chisel ploughs are also used to open land before a disc harrow in dryland systems, and a pass across the slope leaves ridges that slow runoff. Wear of the points changes their rake and depth, so points are checked and replaced as a routine.
A subsoiler is a heavy, narrow tine designed to loosen soil below normal plough depth, to break a plough pan, a traffic pan or a natural hardpan. It works well only when the soil at working depth is dry enough to shatter; in wet subsoil it simply cuts a slot and smears it. Soil failure under a narrow tine was analysed by Godwin and Spoor. Near the surface the soil fails in a crescent that lifts upward and forward, loosening a wedge wider than the tine. Below a critical depth, the soil can no longer escape upward and flows sideways around the tine, compacting rather than loosening. Critical depth increases with tine width and decreases as the soil gets wetter; for a given tine the working depth should stay above it. Wings fitted to the foot and shallow leading tines ahead of the deep tine raise the critical depth and increase the loosened cross-section per unit of draft, which is why modern low-disturbance subsoilers carry them. Rake angle, the angle of the tine face to the horizontal, strongly affects draft and lift: steep rake angles raise draft. Subsoiling is expensive in power and time and its effect lasts only until traffic re-compacts the soil, so controlled traffic is often paired with it. A mole plough is a related drainage implement: a cylindrical foot, the mole, with an expander drawn behind, is pulled through a plastic clay subsoil to form an unlined channel that carries water to field drains.
A disc harrow carries several smaller concave discs mounted on a common shaft to form a gang. The gang is set at a gang angle to the direction of travel; larger gang angles cut and throw more soil and penetrate more, at higher draft. A single-action harrow has two gangs end to end throwing soil outward. A tandem or double-action harrow adds two rear gangs that throw soil back, leaving the surface level. An offset disc harrow has one front gang and one rear gang working in opposite directions, set to one side of the tractor centre line; it can work under tree branches in orchards and, being heavy, is often used for primary tillage of residue-laden land. The side forces of its two gangs are not automatically balanced; balance depends on offset, gang angles and hitch position, and an unbalanced harrow crabs sideways. Spike-tooth harrows drag rigid pegs through the surface to break clods, level and kill weed seedlings. Spring-tooth harrows have curved spring steel teeth that vibrate and suit stony or trashy ground. Blade harrows, such as the bakhar used in the black soils of central India, cut beneath the surface with a horizontal blade to break the crust and kill weeds. Planks and rollers crush clods and firm the seedbed.
A cultivator is a tined implement used for secondary tillage and for weeding. Tines may be rigid, spring-loaded or of spring steel, and carry replaceable soil-working tools: reversible shovels, sweeps that undercut weeds with a wide flat blade, and duck-foot sweeps. The field cultivator used for seedbed preparation covers the full width; the row-crop or inter-row cultivator is guided between crop rows and its tool spacing must be adjusted to the row spacing. Tines are usually staggered in two or three rows so that residue can flow between them. Tine cultivators leave a rougher surface than rotary tools and need tractor drawbar pull rather than PTO power. Hand and animal-drawn versions, such as wheel hoes and multipurpose tool bars, are important in smallholder systems. Depth is held by gauge wheels or by the tractor hydraulics. Speed matters: shovels and sweeps throw more soil at higher speed, which can bury small crop plants in inter-row work, so row-crop cultivation is done with shields or at moderate speed. A cultivator works best on soil that is moist but friable; in dry, hard soil tines ride out, and in wet soil they smear and leave clods.
A rotary tiller has a horizontal rotor, driven from the tractor power take-off, carrying blades on flanges. The blades cut slices of soil and throw them against a rear shield, giving a well-broken seedbed in one pass. L-shaped blades are common for general and wetland work; C-shaped and J-shaped blades suit other conditions. The rotor normally turns in the same direction as the wheels (down-cut), which helps push the machine forward, so the drawbar pull needed is small or even negative, but the total power drawn through the PTO is high. Two numbers describe its action. The kinematic parameter λ is the ratio of blade tip peripheral speed to forward speed, λ = ωR/v; it must exceed 1 for the blade to cut forward, and typical machines work with λ several times larger than 1. The bite length, the forward distance advanced between successive cuts made by blades working in the same plane, is L = v·60/(n·Z), where v is forward speed in m/s, n the rotor speed in rev/min and Z the number of blades acting in one plane per rotor revolution. Written with angular speed ω in rad/s, the same result is L = 2πv/(ωZ). Shorter bite gives finer tilth but more power and more pulverisation. Rotary tillers work well in wet soils and for puddling and residue mixing, but repeated use can over-pulverise the soil and smear a compact layer at blade depth. On two-wheel tractors the rotary tiller is the main implement across much of Asia.
A tillage tool moving through soil must overcome the soil's shear strength (cohesion and internal friction), soil–metal adhesion and friction, the weight of soil lifted, and the force needed to accelerate soil. The first three depend on soil type, moisture and density; the acceleration force rises with the square of speed. Reece expressed the force on a wide blade in the universal earthmoving equation, where the force is the sum of terms for soil weight (proportional to the square of depth), cohesion and adhesion (proportional to depth) and surcharge, each multiplied by a dimensionless factor N that depends on the tool geometry and friction angles, all times the tool width. The resultant soil force on a tool is resolved into three components: draft, the horizontal component parallel to the direction of travel; the vertical component, upward or downward; and the side (lateral) component. A mouldboard plough has a downward suction force and a side force toward the unploughed land. Draft is what the tractor must pull; power at the drawbar is draft times speed. Unit draft, or specific draft, is draft divided by the cross-sectional area of the furrow, usually quoted in N/cm² or kPa; it is a soil and implement property that lets draft be scaled to other widths and depths. Unit draft values vary widely with soil texture, moisture and speed; clay soils need several times the draft of sandy soils.
For planning, the ASABE standard D497 gives the draft of common implements as D = Fᵢ[A + B·S + C·S²]·W·T, where Fᵢ is a dimensionless soil texture adjustment (fine, medium and coarse soils), A, B and C are machine-specific parameters, S is forward speed in km/h, W is machine width in metres or number of tools, and T is tillage depth in cm for major tools (seeding and minor tools omit T). The standard lists the parameters with a range of expected variation that is often ±25–50 %, and the PE examination supplies the standard rather than expecting the values to be memorised. The quadratic speed term shows why doubling speed more than doubles power. From draft, required drawbar power is draft × speed; the tractor engine or PTO power needed is larger, divided by tractive efficiency and transmission efficiency, which belong to the traction subject. The same standard gives the draft of seeding implements per row and of minor tools per unit width. When local measurements exist, they are better than the standard, because soils outside the conditions of the original data can differ greatly; a dynamometer between tractor and implement, or a three-point hitch force transducer, gives the draft directly.
The centre of resistance of a tool is the point through which the resultant soil force can be taken to act. For a trailed implement to run steadily without crabbing or tipping, the line of pull from the tractor hitch point must pass through the implement's centre of resistance. When the tractor wheel tread is wider than the plough cut, the hitch point cannot be placed directly in front of the centre of resistance, so the line of pull is angled in plan view and a side draft results; this side force is carried by the landside or furrow wheel and adds friction and wear. In side view the line of pull is inclined upward from the implement toward the drawbar. If the pull P acts at angle θ above the horizontal, the draft is P cos θ and the vertical component P sin θ lifts the implement and presses down on the tractor's rear axle. On a three-point linkage the upper and lower links, projected in side view, meet at a virtual hitch point; the line of pull runs from the centre of resistance through it. Moving the virtual hitch point changes how much implement weight and soil reaction is transferred to the tractor rear wheels, which is the basis of weight transfer and draft control. Draft control senses force in the top link or lower links and raises or lowers the implement to keep draft nearly constant; position control holds the implement at a set height relative to the tractor. Three-point hitch dimensions are standardised by category in ISO 730.
A seed drill meters seed in a continuous stream and places it in rows at a controlled depth; it is used for small grains such as wheat, barley, rice (direct-seeded), oats and many pulses and grasses. A planter meters individual seeds at a set spacing within the row, which is called precision or single-seed planting; it is used for maize, cotton, soybean, sunflower, sugar beet, groundnut and vegetables. A broadcaster scatters seed over the surface and is followed by a harrow to cover it. A seed-cum-fertiliser drill carries two hoppers and two metering systems and places fertiliser near the seed, often in the same furrow or in a separate band. The main parts of a drill are the frame, seed hopper, metering mechanism, seed tubes, furrow openers, covering devices and press wheels, the ground drive wheel with its chain and sprocket or gear transmission for setting the rate, depth control, and row markers. Seed tubes may be flexible polymer, rubber or spiral steel; they must not kink or block, and their length and shape affect how evenly seeds arrive in the furrow, which matters more for planters. Zero-till drills and no-till planters have heavier frames, strong openers and residue-cutting coulters or row cleaners, because they must cut through residue and untilled soil. Air seeders meter seed centrally and blow it through hoses to many openers; they allow very wide machines.
The furrow opener opens a slot at the right depth for the seed, and its design largely decides seed placement, residue handling and draft. A shoe or runner type opener slides through prepared soil and makes a shallow, clean slot; it needs a clean, well-tilled seedbed. The hoe or tine type (including shovel and chisel openers) penetrates hard or dry soil and is common on Indian and Australian drills; it can place seed into moist soil below a dry surface layer, but it drags residue and bunches it. The single-disc opener cuts through residue and penetrates well; the double-disc opener, two discs meeting at the front to form a V, cuts residue and makes a neat slot and is standard on planters and no-till drills in residue. The inverted-T opener, a narrow tine with a horizontal foot, cuts a slot with a wider base underground and disturbs little soil; it is the typical opener of zero-till drills for wheat after rice in South Asia. Discs need weight to penetrate, and in wet soil they can compact and smear the side walls, which causes poor seed–soil contact and slot opening. Behind the opener, covering devices such as chains, drag bars or closing wheels close the slot, and press wheels firm soil over the seed. Depth uniformity is set by depth-gauge wheels close to the opener; seed depth is a key agronomic target that varies by crop and soil moisture.
Match the machine to the crop, seedbed and residue. Small grains in a tilled seedbed can use a simple tined drill with fluted rollers; sowing into heavy residue needs discs or a straw-managing design; wide-row crops need singulating planters. Row spacing is set by opener position on the tool bar. Machine width should suit tractor power and field size. Before sowing, check that every opener is at the same depth, that tubes are clear, and that the metering drives turn freely. Calibrate the rate (chapter 8). In the field, stop after a short run and dig to check seed depth and spacing, because a stationary calibration does not check placement. Forward speed matters: most plate and fluted-roller planters lose spacing accuracy at higher speed as seeds bounce in the tube, so manufacturers state a speed range; vacuum and belt-delivery planters tolerate more speed. Testing standards for single-seed drills, such as ISO 7256-1, and national test codes set out how spacing, depth and damage are measured.
The fluted roller or fluted feed is the most common drill metering mechanism. A roller with straight longitudinal flutes rotates in the bottom of the hopper; seed fills the flutes and is carried over a lip into the seed tube. Seed rate is changed by sliding the roller to change the exposed length of flutes and by changing roller speed through the gearbox or sprockets. Over most of its range, delivery is close to proportional to exposed length and roller speed, but not exactly at very short exposures, which is why calibration is always done at the working setting. The fluted roller handles a wide range of seeds but can crack large or fragile seeds such as soybean and groundnut if the flute clearance is too small. The internal double-run feed has a wheel with a coarse ribbed face on one side and a fine one on the other; seed runs through the inside of the wheel, and the choice of side suits large or small seeds. In the cup feed, small cups or spoons on the rim of a vertical disc lift seeds out of a hopper and drop them into funnels leading to the tubes; cup size is chosen to suit the seed. Other bulk meters include brush feed, the stationary-opening gravity feed with an agitator, and the metering rollers of central-hopper air seeders, where a single meter feeds a fan-driven stream that is split into rows by a distribution head.
Precision meters try to deliver exactly one seed per cell. The horizontal plate planter has a rotating plate with cells or notches around its edge under the hopper; each cell picks up a seed, a spring-loaded cut-off removes excess seeds, and a knock-out or ejector pushes the seed into the tube. Plates are chosen to match seed size, and graded seed gives the best results. Inclined plates, set at an angle, pick seeds from the bottom of the hopper and are gentler on seed and less sensitive to seed shape. Vertical rotors and cell wheels work similarly. Finger pick-up meters use spring-loaded fingers that trap seeds against a plate. Pneumatic meters use air. In a vacuum meter, a disc with small holes rotates against a vacuum chamber, seeds stick to the holes, a singulator or doubles eliminator knocks off extra seeds, and each seed drops when the vacuum is cut off. Positive-pressure meters use air pressure to hold seeds in cells and blow excess away. Pneumatic meters handle ungraded and irregular seed better and suit higher speeds. For vegetables and potatoes, belt meters, pickers and cup elevators are used. The seed spacing from any cell-type meter is s = distance travelled per meter revolution divided by cells per revolution; with a ground wheel of diameter D, drive ratio i (meter turns per wheel turn) and N cells, s = πD(1 − skid)/(i·N).
A planter's spacing accuracy is measured by recording the spacings between successive seeds on a sticky belt in a laboratory stand or between seedlings in the field. With a theoretical spacing X, Kachman and Smith defined the miss index as the percentage of spacings greater than 1.5X, the multiples index as the percentage of spacings not greater than 0.5X, and the quality-of-feed index as 100 minus both, the percentage of singles. Precision is the coefficient of variation of the spacings classified as singles. These indices are used in ISO 7256-1 style testing and in research. Misses reduce plant population; multiples waste seed and create competing doubles. Other test measures include seed damage (visual cracks, germination loss after metering), flow-rate uniformity between rows for drills, and consistency of rate as the hopper empties and on slopes. Fluted-roller drills are tested for the variation of delivery among rows and for sensitivity to slope and vibration.
Calibration makes the drill deliver the intended seed rate. The standard stationary method is examined often. First, measure the ground drive wheel diameter D and the effective working width W, which for a drill is the number of rows times row spacing, not the frame width. Decide the area to be simulated, for example 1/25 or 1/10 of a hectare. The distance per wheel revolution is πD, corrected for wheel skid or slip. The number of revolutions for the chosen area A is N = A / (πD(1 − s)·W) under the common textbook convention that the effective travel per revolution is reduced by the skid percentage s. Jack up the drill so the drive wheel turns freely, fill the hopper at least partly, set the metering, place a container or bag under each tube, mark the wheel, and turn it N times at about the speed it turns in the field. Weigh the seed from all tubes. Seed rate in kg/ha is the mass collected divided by the area in hectares. If the rate is wrong, adjust exposed length or gear ratio and repeat. Check delivery from each tube; unequal tubes point to a worn or misassembled roller.
Textbooks and examiners differ in how they treat skid. The physical fact is that a ground wheel that skids or slides turns fewer times than a rolling wheel over a given distance; some books therefore divide by (1 − s) and others multiply, depending on whether s is defined relative to the rolling distance or to the actual travel. The safe practice is to measure travel per revolution in the field, by counting revolutions over a measured distance of 30–50 m in the working condition, and to use that value. In an examination, read the question's wording and apply it consistently. Other common errors are using radius instead of diameter, using frame width instead of rows × spacing, forgetting to convert cm to m and m² to ha (1 ha = 10 000 m²), and giving the mass per tube instead of the total. When the rate must be proportional to seeds rather than mass, as for planters, convert using the thousand-seed mass, germination and expected field emergence. Seeds needed per hectare equal the target plants per hectare divided by the fraction expected to establish (germination times field emergence). The seed rate in kg/ha then equals target plants per m² × thousand-seed mass in grams / (100 × establishment fraction). For example, 250 plants per m² of a seed with a thousand-seed mass of 40 g and 85 % establishment needs 250 × 40 / 85 ≈ 118 kg/ha.
After stationary calibration, sow a measured area in the field, for example 100 m of run, and weigh the seed used from a marked hopper level, or refill to the mark and weigh the refill. This catches errors from wheel slip, vibration and speed. Fertiliser metering in seed-cum-fertiliser drills is calibrated the same way, but the target is set by nutrient: kg of product = kg of nutrient needed divided by the nutrient fraction of the product. For example, urea contains 46 % nitrogen, so each kg of N needs about 2.17 kg of urea. Fertiliser flow varies with humidity, granule size and hopper level more than seed flow does, and fertiliser is corrosive, so clean the metering after use. For planters, calibration checks spacing rather than mass: count seeds dropped over a set number of wheel turns, or measure spacing on a test run, and compare with the spacing given by the plate cells and drive ratio. Plant population per hectare equals 10 000 divided by the product of row spacing and within-row spacing in metres.
Transplanting rice gives the crop a head start over weeds and allows a shorter main-field period, and it has traditionally been done by hand, which needs a large amount of labour at a single peak. Mechanical transplanters were developed in East Asia and are now common across South and South-East Asia. Most machines need seedlings raised as a mat nursery: pre-germinated seed is sown densely on a thin layer of soil in trays or on a polythene sheet, producing a mat with interlocked roots that can be cut into blocks. Young seedlings, commonly two to three weeks old at the two- to three-leaf stage, are used; the ideal age and height depend on the machine and variety, and older or taller seedlings jam the pickers. The main field is puddled and levelled and allowed to settle, so that the machine floats and the planted seedlings stand upright; it is transplanted with shallow standing water. Poor levelling is the most common cause of missing and buried hills.
A mat-type transplanter carries the seedling mats on an inclined tray that moves sideways step by step. A rotary or crank-type picking fork (planting finger) descends, cuts a small block of seedlings from the bottom edge of the mat, carries it into the soil and releases it. The tray then shifts sideways by a fixed amount and the mat is fed downward so the next pick takes fresh seedlings. The number of seedlings per hill is set by the lateral shift and vertical feed, which fix the size of the block picked. Hill spacing along the row is set by the ratio of planting-arm speed to forward speed, usually through a gear lever. Row spacing is fixed by the machine's design; many walk-behind machines use about 30 cm, while some use narrower spacing. Walk-behind machines commonly plant four to eight rows; riding types plant more and are faster. Floats or sledges support the machine on the puddle. Manual transplanters, pushed and operated by hand, also exist. Performance is judged by field capacity, missing-hill percentage, buried and floating hills, damaged seedlings, seedlings per hill, planting depth and hill spacing uniformity. Hill density per m² is 1 divided by the product of row and hill spacing in metres.
Vegetable seedlings are transplanted as bare-root plants or, increasingly, as plugs raised in cell trays. Semi-automatic transplanters are the most common type: one operator per row drops seedlings into cups on a rotating carousel, into flexible grippers on a rotating disc, or between chain-mounted fingers, and the mechanism releases each plant into a furrow opened by a shoe, after which press wheels firm the soil and water may be added. Output per row is limited by how fast the operator can feed plants, so these machines work slowly and need crews. Fully automatic transplanters extract plugs from trays with needles or pins and are used in high-value vegetables where tray and plug dimensions are standardised. Mulch-laying transplanters punch holes through plastic film. Plant quality at transplanting, uprightness, planting depth and missed plants are the usual test measures. Related machines include potato planters, which use cups on a belt or picker arms to place tubers, and sugarcane cutter-planters, which cut canes into setts, place them in a furrow with fertiliser and chemical treatment and cover them.
Granular fertilisers are applied by broadcasting over the whole surface or by placing them in bands or points near the seed or root zone. Centrifugal (spinning disc) broadcasters drop fertiliser onto one or two rotating discs with vanes that throw it over a width much wider than the machine; pendulum or oscillating-spout spreaders swing a tube from side to side. Pneumatic spreaders meter product centrally and blow it along a boom to deflectors, giving a more even pattern that is less affected by granule properties. Full-width drop or gravity spreaders meter through openings along a hopper. Placement devices, on seed-cum-fertiliser drills and separate applicators, use fluted rollers, star wheels, auger feeds, edge-cell wheels, belts or chains to meter product into tubes. Deep placement of urea granules or briquettes in puddled rice, by hand or by simple applicators, is used in parts of South and South-East Asia to reduce nitrogen loss.
A spinning disc throws each granule a distance that depends on granule size, density, shape and surface, disc speed, vane shape and drop point. The pattern across the swath is roughly triangular or trapezoidal, heaviest in the centre, so adjacent passes must overlap. The bout width, the distance between tractor passes, is chosen so that the overlapped pattern is even; it is less than the total throw width. Uniformity is measured by laying collecting trays across the swath and computing the coefficient of variation of the amounts, for example under ASABE S341 or the ISO 5690 test methods. Acceptable CV targets differ by country and product, so use the local guideline. Blends segregate when granules of different size or density are thrown different distances, so different nutrients can land in stripes. Calibration of a broadcaster: measure the mass flow rate Q from the opening at a setting, then application rate (kg/ha) = Q (kg/min) × 60 × 10 / (bout width in m × speed in km/h), because width times speed divided by 10 gives ha/h. Edge-spreading devices limit throw at field boundaries and next to water.
Liquid fertilisers are applied with sprayer-type boom equipment using streaming nozzles, dribble bars, or injected into soil with knives; they meter accurately and blend easily. Anhydrous ammonia, used mainly in North America, is a pressurised liquid injected through knives and sealed in the soil; handling it requires specific safety training and equipment because it is toxic and causes severe burns. Solid manure is applied with rear-discharge spreaders with beaters, and liquid slurry with tankers; low-emission methods such as trailing hose, trailing shoe and shallow injection are required in several European countries to reduce ammonia loss. Fertilisers are hygroscopic and corrosive. Store them dry, avoid caked product, which meters erratically, and wash and dry metering parts after use. Hoppers and metering parts are made of stainless steel or plastics for this reason. Operators should wear gloves and avoid inhaling dust. Before each season check spinner vanes for wear, because worn vanes change the throw and the pattern, and repeat the tray test when the product or granule size changes. Keep a record of settings for each product so that the calibration does not start from zero every time.
Field capacity is the rate at which a machine covers land. Theoretical field capacity is the rate if the machine worked all the time at full rated width and speed: TFC (ha/h) = w (m) × v (km/h) / 10. The factor 10 arises because 1 m × 1 km = 1000 m² = 0.1 ha. Effective field capacity is the actual area covered divided by the total time spent in the field, including turning, overlapping, refilling seed and fertiliser, adjustments, unclogging and small repairs. Field efficiency is the ratio of effective to theoretical field capacity, expressed as a percentage. Material capacity, used for harvesting and handling machines, is mass processed per unit time. Field efficiency falls when fields are small or irregular, when rows are short so turns are frequent, when hoppers must be refilled often, and when the operator overlaps too much. Seeding and planting equipment usually has lower field efficiency than tillage because of stops to fill and check; ASABE D497 tabulates typical ranges and representative values for each implement, and these vary with farm conditions.
The width used in field capacity must be the effective width actually worked. For a mouldboard plough it is the number of bottoms times the width of cut per bottom. For a seed drill it is the number of rows times row spacing. For a disc harrow or sprayer it allows for overlap between passes. For a spinning broadcaster it is the bout width, not the total throw width. Where overlap is a percentage of width, the effective width is the width times (1 − overlap fraction). Speed must also be the actual ground speed; wheel slip of the tractor reduces actual speed below the theoretical speed from engine revolutions and gear ratio. Measure it by timing the machine over a marked distance in working condition, for example 50 m, and dividing. For a rotary tiller or cultivator working alongside the previous pass, a small overlap is deliberate to avoid missed strips; the effective width is what remains after that overlap. Getting effective width right matters more than any other input, because an error in width carries straight into seed rate, field capacity and cost per hectare.
Field capacity lets a manager answer two practical questions. How long will a job take? Time (h) = area / EFC. What width is needed to finish in the available time? Solve w = 10 × area / (v × field efficiency × hours available). Hours available are the number of suitable days in the operating window times the working hours per day, and the probability of a day being workable depends strongly on climate and soil, so machinery management uses local records of workable days. Timeliness cost, the yield or quality lost when an operation is done later than the optimum, is the reason a larger machine can be cheaper overall: a larger machine costs more to own but finishes sooner. In smallholder regions the same logic drives custom hiring, where one machine serves many farms, and the time window for sowing after the previous harvest, such as wheat after rice, often decides which machine is chosen.
The cost of owning and operating a machine is split into fixed (ownership) costs, which occur whether or not the machine is used, and variable (operating) costs, which rise with use. Fixed costs are depreciation, interest on the investment, and taxes, insurance and housing. Depreciation is the loss in value with age and use. Straight-line depreciation is (P − S)/L per year, where P is purchase price, S salvage value and L life in years. The declining-balance method takes a fixed fraction r of the remaining value each year, so the value after n years is P(1 − r)ⁿ; if salvage is to be reached at the end of the life, r = 1 − (S/P)^(1/L). The sum-of-years-digits method depreciates year k by (L − k + 1)/[L(L + 1)/2] × (P − S), giving large early and small later charges. The sinking-fund method treats depreciation as an annual deposit that grows with interest to P − S. Interest on investment is commonly charged on the average investment, (P + S)/2 × i, where i is the interest rate; a more exact approach uses the capital recovery factor, which combines depreciation and interest into one uniform annual cost. Taxes, insurance and housing are often charged as a small percentage of the purchase price each year; the percentage differs by country. Many textbook problems assume a salvage value of 10 % of purchase price; this is an assumption, not a law.
Variable costs are repair and maintenance, fuel, lubricants and labour, plus for implements the wear parts such as shares, discs and sweeps. Repair and maintenance costs rise with accumulated hours; ASABE D497 expresses accumulated repair cost as a fraction of purchase price, RF1 × (h/1000)^RF2, with repair factors listed for each machine type. In simple problems repairs are often taken as a fixed percentage of the purchase price per 100 hours or per year. Fuel cost is fuel consumption per hour times fuel price; lubricant cost is often taken as a percentage of fuel cost. Labour cost is the wage times hours, usually multiplied by a factor above 1 for time spent on travel, servicing and preparation. The cost of an implement operation should include the share of the tractor's cost that drives it. Wear parts on tillage tools, such as shares, sweeps, points and discs, can be a large part of implement operating cost in abrasive sandy or stony soils, and are best costed from local replacement records. Where fuel is subsidised or labour is family labour, economists may use shadow prices rather than market prices; say which basis is used.
Cost per hour = annual fixed cost / annual hours of use + variable cost per hour. Cost per hectare = cost per hour / effective field capacity. Because fixed cost is spread over use, cost per hectare falls sharply as annual use rises; a machine used for only a few hours a year is very expensive per hectare. The break-even use between owning and hiring is the annual area at which the costs are equal: area = annual fixed cost / (custom hire charge per ha − variable cost per ha of owning). Below this area it is cheaper to hire; above it, cheaper to own, other things being equal. Timeliness, availability of hire services when needed, and the operator's skill also enter the decision. Custom hiring centres, promoted in India under farm mechanisation schemes and common elsewhere as contractor services, make expensive implements such as zero-till drills, laser levellers and transplanters available to small farms by spreading fixed cost over many users. Machinery replacement decisions compare the rising repair cost of an old machine with the ownership cost of a new one; replace when the average annual cost is at its minimum.
As a student you will be asked to name the parts of a plough bottom, explain suction and disc angles, sketch metering mechanisms and, above all, calibrate a seed drill and cost a machine. Practise the calibration on a real drill in the workshop: measure the wheel, count rows, jack it up, turn it the computed number of times and weigh the seed. Do the same field-capacity and cost problems until you can solve them in two minutes without notes. Keep a sheet of the formulas and the unit conversions (1 ha = 10 000 m²; km/h to m/s divide by 3.6), because most exam errors are unit slips, not physics.
After five years in extension, a custom hiring centre, a dealer's service team or a testing station, your work is choosing, setting and checking machines in real fields. You calibrate drills before each season and each seed lot, set plough suction and hitching so the implement runs straight, match implement width to tractor power, decide between tined and disc openers for residue, check transplanter missing hills, and prepare cost-per-hectare figures for hire rates. You explain to farmers why stationary calibration must be followed by a field check and why a worn share or blocked tube ruins a stand.
With twenty-five years' experience you design mechanisation programmes and test protocols. You decide which implements a subsidy or hire scheme should support in a region, based on soils, cropping calendars, workable days and farm sizes; set test codes and acceptance criteria for drills, planters and transplanters; judge conflicting test reports; and manage fleets where timeliness, repair cost and replacement age drive profit. You also weigh the soil effects of tillage systems, such as plough pans from puddling or rotary tillage, against short-term convenience.
At doctoral level with long field experience you work on the mechanics and the evidence. Research areas include soil–tool modelling (analytical, finite-element and discrete-element methods) for low-draft tines and openers, residue–opener interaction in no-till, pneumatic and electric-drive precision metering with variable-rate control, seed-tube dynamics at high speed, and field experiments that link placement accuracy to yield. You design long-term tillage trials, review draft datasets behind standards, and advise policy on conservation agriculture, stubble management and small-farm mechanisation with honest statements of uncertainty.
This manual does not give numerical unit-draft values, D497 A/B/C parameters, repair factors or field-efficiency tables, because they vary by soil, machine and edition and must be taken from the current standard or local test data. It does not give the exact location of a plough bottom's centre of resistance, which textbooks state differently. Detailed design of plough bottoms, disc geometry and metering plates, animal-drawn implement ergonomics, sugarcane and potato planters, and country-specific test codes (BIS, PAES/PNS, OECD) are covered only briefly. Traction, tractor hydraulics and full machinery management are in their own subjects.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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