Unit 4: Sowing and planting machines - Subjective Questions

A seed metering mechanism is the part of a sowing or planting machine that removes seed from the hopper and delivers it to the seed tube or furrow at a controlled rate.

Main functions:

• Pick or release the required quantity of seed from the hopper.
• Maintain a uniform seed rate per unit area.
• Provide the required seed-to-seed or hill-to-hill spacing.
• Minimize seed damage, missing, and multiple dropping.
• Deliver seed continuously under varying field conditions.

Requirements of an efficient mechanism:

• Accurate metering over the desired range of seed rates.
• Suitability for the size, shape, and physical properties of the seed.
• Uniform operation despite changes in hopper seed level or machine speed.
• Low seed damage and low power requirement.
• Easy calibration, adjustment, cleaning, and maintenance.
• Resistance to clogging and wear.

Seed metering mechanisms may be classified as follows:

• Fluted-roller mechanism: A rotating roller containing longitudinal flutes carries seed from the hopper to the seed tube. The seed rate is changed by varying the exposed flute length or roller speed.
• Internal double-run mechanism: A feed wheel has coarse and fine seed passages. The coarse side meters large seeds, while the fine side meters small seeds.
• Cup-feed mechanism: Cups mounted on a rotating disc or chain pick up seeds and discharge them into the seed tube. It is generally used for bold seeds.
• Cell or plate mechanism: Cells on a horizontal, inclined, or vertical plate select individual seeds and release them at regular intervals.
• Pneumatic mechanism: Vacuum or positive air pressure holds individual seeds against holes in a rotating plate or drum and releases them at the required location.
• Auger or screw mechanism: A rotating helical screw conveys and meters seed continuously, particularly in specialized drills.

Fluted rollers and double-run mechanisms normally provide continuous metering, whereas cell plates and pneumatic mechanisms can provide precision singulation.

Construction:

• It consists of a cylindrical roller with longitudinal flutes.
• The roller is fitted at the bottom of the seed box.
• A shaft driven by the ground wheel rotates the roller.
• An adjustable gate and feed cup guide seed toward the seed tube.

Working:
As the roller rotates, seeds enter the exposed flutes. The flutes carry a measured volume of seed out of the hopper and discharge it into the seed tube. The amount delivered is approximately proportional to roller speed and exposed flute length.

Seed-rate adjustment:

• Increase or decrease the exposed length of the flutes.
• Change the drive ratio using sprockets or gears.
• Adjust the feed gate to suit seed size.

Advantages:

• Simple, durable, and inexpensive.
• Provides reasonably uniform continuous seed flow.
• Suitable for cereals and many small grains.
• Easy to calibrate and maintain.

Limitations:

• Does not accurately place single seeds.
• May damage very delicate seeds.
• Performance can be affected by seed size variation, excessive speed, or improper gate setting.

An internal double-run mechanism consists of a rotating feed wheel mounted below the seed box. The wheel has two sets of seed passages on its inner surface:

• Coarse passages for large seeds such as wheat, peas, and gram.
• Fine passages for small seeds such as mustard and other small grains.

Working:

• Seed enters the selected side of the feed wheel through an adjustable opening.
• Rotation of the ground-wheel-driven feed shaft carries seed through the internal passages.
• The seed is discharged into a funnel and then passes through the seed tube to the furrow.
• The unused side may be closed or reversed according to the seed being sown.

Suitability for different seeds:
The two differently sized passage systems allow the same mechanism to meter both coarse and fine seeds. The seed rate can also be altered by changing the feed-wheel speed or the opening of the seed gate.

Advantages:

• Versatile for a wide range of seed sizes.
• Positive and reasonably uniform feed.
• Compact and dependable.

Limitations:

• Less precise than cell-type mechanisms for single-seed placement.
• Incorrect selection of the coarse or fine side may cause irregular feeding or seed damage.

Thus, mechanical plates are economical and suitable for graded seed, while pneumatic mechanisms are preferred where high precision and uniform plant spacing are required.

Let:

• = effective width of the drill in m,
• = diameter of the ground wheel in m,
• = number of ground-wheel revolutions,
• = simulated area in ha,
• = mass of seed collected in kg.

The distance traveled in revolutions is:

The area covered in square metres is:

Since :

Therefore, the seed rate is:

For a drill having openers at row spacing :

Stationary calibration procedure:

• Fill the seed box to a representative level.
• Raise the drill so that the ground wheel rotates freely.
• Place collection bags under all seed tubes.
• Mark the ground wheel and rotate it through a selected number of revolutions.
• Collect and weigh the discharged seed.
• Calculate the seed rate using the above equation.
• Adjust exposed flute length, gate opening, or sprocket ratio.
• Repeat until the desired rate is obtained.

Allowances may be made for field wheel slip and differences between laboratory and field conditions.

The choice depends on crop geometry, seed value, seed size, available machinery, field condition, and the required plant population.

Main components:

• Seed hopper.
• Adjustable feed gate or metering opening.
• Agitator to prevent bridging.
• Spinning disc, oscillating spout, or air-delivery unit.
• Vanes or fins for distributing seed.
• Ground-wheel, power-take-off, electric, or hydraulic drive.
• Rate-control and shut-off mechanism.

Working:
Seed flows from the hopper through the calibrated opening onto a rapidly rotating disc. Vanes on the disc accelerate and throw the seed outward in a fan-shaped pattern. Adjacent passes must overlap correctly to obtain uniform coverage. The scattered seed is usually incorporated using a harrow or another tillage implement.

Advantages:

• High field capacity.
• Simple construction and operation.
• Suitable for small seeds, cover crops, and pasture establishment.
• Useful where row placement is unnecessary.

Disadvantages:

• Nonuniform seed distribution may occur due to wind, seed properties, or poor overlap.
• Depth and seed-to-seed spacing are not controlled.
• More seed is generally required.
• Seed left on the surface may suffer from birds, drying, or poor germination.
• Inter-row mechanical weeding is difficult.

A seed drill places seed in continuous rows at a controlled rate and depth.

Major components and functions:

• Frame and hitch: Support the machine and connect it to the tractor or animal-drawn unit.
• Seed box or hopper: Stores the seed.
• Agitator: Prevents seed bridging and maintains flow toward the metering units.
• Seed metering mechanism: Delivers seed at the selected rate.
• Ground wheel and transmission: Drive the metering shaft in proportion to forward travel.
• Seed tubes: Convey metered seed to the openers.
• Furrow openers: Form furrows at the required row spacing and depth.
• Depth-control mechanism: Regulates opener penetration.
• Covering device: Covers seed with soil.
• Press wheels: Firm the soil around the seed and improve seed-soil contact.
• Markers: Indicate the path for the next pass.

Working:
Forward movement rotates the ground wheel. Through gears, chains, or sprockets, it drives the metering shaft. Metered seed falls through the seed tubes into furrows made by the openers. Covering devices close the furrows, and press wheels compact the soil lightly over the seed.

Advantages of a seed drill:

• Places seed at a more uniform depth.
• Maintains definite row spacing.
• Provides better seed-soil contact and more uniform germination.
• Reduces seed rate compared with broadcasting.
• Covers seed immediately and protects it from birds and weather.
• Makes inter-row weeding, fertilizer placement, and crop inspection easier.
• Produces a more uniform crop stand.

Disadvantages of a seed drill:

• Has a higher initial cost than simple broadcasting equipment.
• Requires calibration and skilled adjustment.
• Metering parts and seed tubes may clog.
• Poorly prepared or residue-covered fields can interfere with openers.
• Turning and transport are more difficult with wide drills.
• Incorrect depth, speed, or opener pressure may produce poor emergence.

Broadcasting has higher capacity and simpler operation, but a seed drill generally gives better establishment because it controls seed rate, row position, and depth.

Common furrow openers include:

• Shoe opener: Has a pointed shoe that pushes soil aside. It is simple and suitable for well-prepared, light-to-medium soils with little residue.
• Shovel opener: Uses a wider shovel to form a broad furrow. It is useful for general drilling but causes more soil disturbance.
• Hoe opener: Penetrates hard soil effectively and can operate at greater depth. It is suitable for firm soils but may collect surface residue.
• Single-disc opener: A rotating concave disc cuts soil and some residue. It performs better than fixed openers in trashy fields but may exert side forces.
• Double-disc opener: Two angled discs form a V-shaped furrow. It provides accurate placement and performs well at moderate speed, though penetration may be limited in very hard soil without sufficient downforce.
• Inverted-T opener: Creates a narrow vertical slot with a horizontal base. It is used in reduced-tillage or direct-drilling conditions and limits soil disturbance.

Selection depends on soil hardness, moisture, crop residue, required depth, operating speed, available downforce, and acceptable soil disturbance.

• Seed rate: An excessive rate causes overcrowding, competition, lodging, and unnecessary seed cost. A low rate produces gaps and reduces plant population.
• Row spacing: Narrow rows improve ground coverage but may restrict inter-row operations. Wide rows facilitate weeding and earthing-up but may underuse field space if unsuitable for the crop.
• Depth of sowing: Shallow placement may expose seed to drying or birds. Excessive depth delays emergence and may prevent weak seedlings from reaching the surface. Depth should suit seed size, soil texture, and moisture location.
• Forward speed: Excessive speed increases opener bounce, depth variation, seed-tube ricochet, misses, multiples, and poor covering. Very low speed reduces field capacity.
• Wheel slip: In a ground-wheel-driven machine, slip reduces actual metering-shaft revolutions per unit field distance and may lower the seed rate. It also makes laboratory calibration differ from field output.

Good performance requires correct calibration, suitable operating speed, stable opener depth, proper tire condition, and periodic checks of actual field population.

A row-crop planter is a machine that meters and places seeds in rows at predetermined row spacing, seed spacing, and depth. It is commonly used for crops such as maize, cotton, soybean, groundnut, and sunflower.

Components:

• Main frame, hitch, and toolbar.
• Seed hoppers for individual rows.
• Seed metering units.
• Ground-wheel or hydraulic/electric drive.
• Transmission and rate-selection system.
• Row cleaners or residue managers where required.
• Furrow openers.
• Gauge wheels and depth-control system.
• Seed tubes or delivery belts.
• Seed firmers, covering devices, and press wheels.
• Row markers and optional monitoring sensors.

Working sequence:

1. Row cleaners clear residue from the planting strip.
2. Openers create furrows at the selected depth.
3. Ground-wheel movement or another drive rotates each metering unit.
4. The meter selects individual seeds and releases them at timed intervals.
5. Seed travels through the delivery system and reaches the furrow.
6. A seed firmer may press it into moist soil.
7. Closing and press wheels cover the seed and provide suitable compaction.

Correct synchronization of travel speed and meter speed determines seed spacing.

Let:

• = row spacing in m,
• = plant-to-plant spacing in m,
• = theoretical plant population in plants per hectare.

The ground area allotted to one plant is:

Since one hectare contains , the theoretical plant population is:

If the desired population and row spacing are known, the required plant spacing is:

For m and m:

Therefore, the theoretical population is approximately:

The actual field population will normally be lower because of misses, non-germinating seeds, seedling mortality, and field losses.

Construction:

• Potato hopper.
• Agitator or flow-control device.
• Cup-belt, picker-wheel, or elevator-type metering mechanism.
• Furrow opener.
• Fertilizer attachment where provided.
• Seed delivery chute.
• Covering discs or ridging bodies.
• Ground wheels, transmission, frame, and hitch.

Working:
Seed tubers or cut sets move from the hopper toward the metering unit. Cups or pickers collect individual tubers and carry them to the discharge point. The tubers drop through a chute into a furrow at approximately uniform intervals. Covering discs close the furrow and usually form a ridge over the planted row.

Advantages:

• Performs furrow opening, metering, placement, covering, and ridging in one operation.
• Increases field capacity and reduces labor.
• Improves row spacing and planting depth.
• Produces more uniform tuber spacing than manual planting.

Limitations:

• Irregular tuber size causes misses or doubles.
• Cups and pickers can damage sprouts or cut seed pieces.
• Requires proper grading and adjustment.
• High speed increases placement errors.
• Initial cost and maintenance requirements are comparatively high.

A drill is appropriate when exact within-row spacing is unnecessary, while a planter is selected when individual plant spacing strongly affects crop performance.

Transplanting is the operation of transferring seedlings from a nursery, tray, or mat to the main field at the required spacing and depth.

Classification by power source:

• Manual transplanters: Operated entirely by human effort.
• Animal-drawn transplanters: Pulled by animals, with manual or mechanical seedling feeding.
• Tractor-mounted or tractor-drawn transplanters: Powered or transported by a tractor.
• Self-propelled transplanters: Have their own engine, transmission, and planting system.

Classification by seedling handling:

• Hand-fed or semi-automatic machines: Operators place individual seedlings into cups, fingers, pockets, or revolving carousels.
• Automatic machines: Seedlings are automatically separated from trays or mats and supplied to the planting mechanism.
• Mat-type rice transplanters: Portions of a seedling mat are picked and inserted into puddled soil.
• Plug-seedling transplanters: Individual plug seedlings are removed from cellular trays and placed in prepared soil.
• Bare-root seedling transplanters: Loose seedlings are manually or mechanically fed to gripping and placement units.

Classification is also possible according to crop, number of rows, riding or walking operation, and planting mechanism.

Main components:

• Engine and transmission.
• Drive wheels, cage wheels, or flotation wheels.
• Steering and control system.
• Seedling platform or mat trays.
• Seedling-feed mechanism for lateral and longitudinal movement.
• Pickup forks or planting fingers.
• Planting-arm mechanism.
• Float or skid for following the puddled field surface.
• Depth, hill-spacing, and seedlings-per-hill adjustments.
• Row marker.

Working:

• Seedling mats are placed on the inclined platform.
• A feed mechanism moves the mat sideways and downward by a controlled amount.
• Reciprocating or rotary planting fingers separate a small group of seedlings from the mat.
• The fingers move downward, insert the roots into puddled soil, and withdraw while leaving the seedlings upright.
• Forward movement and planting-arm motion are synchronized to obtain the selected hill spacing.
• The row spacing is fixed by the arrangement of the planting units.
• Floats support the machine, smooth the surface, and help maintain planting depth.

Properly prepared seedling mats, uniform puddling, shallow standing water, and correct adjustments are essential for good performance.

Construction:

• Tractor hitch and main frame.
• Seedling trays and operator seats.
• Rotating carousel, cups, pockets, or flexible planting fingers.
• Furrow opener.
• Gauge or press wheels.
• Closing wheels.
• Ground-wheel drive and spacing transmission.
• Optional fertilizer and watering attachments.

Working:
Operators remove plug or bare-root seedlings and place them individually into rotating cups or pockets. The ground-wheel-driven mechanism carries each seedling to the discharge point in synchronization with forward travel. The furrow opener forms a slot, the planting unit places the seedling at the required depth, and closing or press wheels firm soil around the roots. Fertilizer or water may be applied near each plant.

Advantages:

• Higher field capacity than manual transplanting.
• More uniform row spacing, plant spacing, and depth.
• Reduced labor requirement and operator fatigue per unit area.
• Better suitability for subsequent mechanical interculture.

Disadvantages:

• Feeding rate is limited by operator skill and fatigue.
• Misses occur if a cup is not filled in time.
• Uniform, strong seedlings are required.
• Machine cost, maintenance, and tractor requirement may be significant.
• Performance declines in cloddy, stony, very wet, or poorly prepared soil.

Factors affecting transplanting quality:

• Seedling condition: Uniform age, height, root development, moisture, and stem strength improve feeding and survival.
• Nursery or tray quality: Correct mat thickness, plug integrity, and root binding prevent breakup during handling.
• Field preparation: A level, fine, and uniformly firm seedbed helps maintain depth and vertical placement.
• Soil moisture: Dry soil gives poor root contact, while excessive moisture can cause wheel slip and weak anchorage.
• Machine adjustment: Planting depth, row spacing, hill spacing, seedlings per hill, finger timing, and closing-wheel pressure must be correct.
• Forward speed: Excessive speed increases misses, damaged seedlings, and irregular spacing.
• Operator performance: Timely feeding is critical in semi-automatic machines.

Advantages:

• Saves labor and time during peak planting periods.
• Provides uniform crop geometry and planting depth.
• Increases field capacity and supports timely establishment.
• Facilitates mechanical weeding, spraying, and harvesting.
• Can reduce drudgery and establishment cost on suitable areas.

Limitations:

• Requires uniform seedlings and careful nursery management.
• Initial investment and maintenance costs are high.
• Small, irregular, or poorly leveled fields reduce efficiency.
• Missing hills may require manual gap filling.
• Skilled adjustment, operation, and repair facilities are needed.