Unit 4: Sowing and planting machines

I. Orientation — Principles of crop establishment

Sowing places seeds in the soil, while planting places larger propagules—such as tubers, bulbs, setts, or seedlings—at agronomically suitable positions. Machinery must deliver the required population uniformly without excessive seed damage, missed locations, or unnecessary soil disturbance.

• Governing principle: A ground wheel, tractor power take-off (PTO), hydraulic motor, or electric motor drives a metering and delivery system in proportion to forward travel.
• Major objectives:
  • Place the correct quantity of seed or planting material per hectare.
  • Maintain specified row spacing, within-row spacing, and depth.
  • cover and compact soil sufficiently for seed–soil contact.
  • Minimize mechanical injury and variation between rows.
• Important field variables: Seed size and shape, germination percentage, soil moisture, tilth, residue level, slope, operating speed, wheel slip, and machine adjustment influence performance.
• Common performance terms:
  • Seed rate: Mass of seed sown per unit area, usually kg/ha.
  • Seed spacing: Distance between consecutive seeds in a row, usually cm.
  • Miss index: Proportion of expected seed positions receiving no seed.
  • Multiple index: Proportion receiving two or more seeds.
  • Field capacity: Area covered per unit time, normally ha/h.
• General machine sequence: Open furrow → meter material → convey or drop it → place at depth → cover soil → press or firm the row.

II. Seed Metering Mechanism — Controlled delivery from the hopper

A. Basics of seed metering mechanism

A seed metering mechanism separates seed from the bulk in the hopper and discharges it at a controlled mass or number per unit of machine travel.

• Basic functions:
  • Agitation: Prevents bridging and maintains seed flow toward the outlet.
  • Selection: Collects a measured volume or individual seeds.
  • Release: Discharges seed into the seed tube at a regular rate.
  • Synchronization: Relates meter speed to ground-wheel travel so output per hectare remains approximately constant.
• Essential requirements: A good meter should have uniform output, low seed damage, easy calibration, minimal clogging, suitability for different seed sizes, and limited sensitivity to hopper level or field vibration.
• Volumetric metering mechanisms:
  • Fluted roller: Longitudinal flutes carry measured quantities beneath an adjustable gate; commonly used for cereals in seed drills.
  • Internal double-run feed: A rotating wheel has coarse and fine cells on opposite sides, allowing large or small seeds to be metered.
  • Cup or spoon feed: Cups lift seeds from the hopper and release them into delivery tubes; useful where positive lifting is needed.
  • Auger feed: A rotating screw conveys seed at a rate governed by pitch, diameter, and rotational speed.
• Precision metering mechanisms:
  • Horizontal or inclined plate: Cells around a rotating plate pick up individual seeds; plate-cell size must match the seed.
  • Vertical plate: Cells on a vertical disc select seeds and release them near the seed tube.
  • Pneumatic meter: Vacuum holds one seed over each disc hole; a singulator removes doubles, and loss of vacuum releases the seed.
  • Finger pickup: Spring-loaded fingers capture and carry individual maize seeds before releasing them into a belt or tube.
• Drive system: Sprockets, chains, gears, shafts, or electronic controls set the ratio between ground-wheel rotation and meter rotation. Changing this ratio changes seed rate or seed spacing.
• Factors causing irregularity: Excessive speed produces bouncing and poor cell filling; wheel slip reduces meter rotation relative to actual distance; unsuitable cell size causes misses, doubles, or seed cracking.
• Calibration relationship:

R = (M × 10,000) / (π × D × N × W)

• (R) = seed rate, kg/ha
• (M) = seed collected during calibration, kg
• (D) = effective ground-wheel diameter, m
• (N) = number of wheel revolutions
• (W) = effective machine width, m

• Calibration example: If (M=0.75) kg, (D=0.60) m, (N=20), and (W=2.0) m, the simulated area is (π×0.60×20×2=75.4\text{ m}^2), giving approximately (99.5\text{ kg/ha}).

III. Methods of Seed Sowing — Placement of seed in the field

A. Methods of seed sowing: components

Different sowing methods use different placement devices, although most mechanized systems share a frame, hopper, drive, metering unit, furrow opener, delivery tube, covering device, and controls.

• Broadcasting equipment: Includes a hopper, adjustable feed gate, agitator, and hand-operated or power-driven spinning disc. Aerial broadcasting uses an aircraft-mounted hopper and spreader.
• Seed drill: Uses a seed box, fluted or double-run meters, ground-wheel drive, seed tubes, furrow openers, covering chains, and depth-control wheels.
• Seed-cum-fertilizer drill: Adds a fertilizer box, separate metering mechanism, fertilizer tubes, and openers that prevent harmful direct contact between concentrated fertilizer and seed.
• Dibbling equipment: Contains a pointed jaw or punch, seed chamber, metering device, and depth stop; powered dibblers may use rotating punch wheels.
• Hill-drop planter: Uses a precision meter that releases a selected group of seeds at fixed intervals rather than a continuous stream.
• Check-row planter: Incorporates seed hoppers, plates, furrow openers, and a check wire with regularly spaced buttons that actuate seed release in both directions.
• No-till drill: Uses residue-cutting coulters, narrow openers, high-downforce springs, metering units, gauge wheels, and press wheels to sow without prior tillage.

B. Methods of seed sowing: working

Each method establishes a crop through a distinct pattern of seed distribution, ranging from random surface spreading to accurate placement of single seeds.

• Broadcasting: Seed flows through a gate onto a rotating disc and is thrown over the soil surface. Harrowing or planking afterward provides shallow coverage.
• Drilling: The ground wheel drives the meter; seed passes through tubes into continuous furrows, after which covering devices close and firm the rows.
• Dibbling: Holes are formed at predetermined row and plant spacings, one or more seeds are deposited in each hole, and soil is returned over them.
• Hill dropping: The meter accumulates or selects several seeds and releases each group at regular travel intervals, producing spaced hills along rows.
• Check-row planting: Buttons on a stretched check wire trip the seed mechanism at fixed points. Aligning successive passes produces rows both longitudinally and transversely.
• Precision sowing: Cells, fingers, or pneumatic holes singulate seeds. The meter releases each seed at calculated intervals, and a press wheel stabilizes its depth.
• No-till sowing: A coulter cuts residue, an opener creates a narrow slot, seed is placed, and press wheels close the slot with minimal soil disturbance.
• Operational sequence: Before work, operators select the meter, set the transmission ratio, calibrate output, adjust opener depth, and verify seed distribution during a short field run.

C. Methods of seed sowing: advantages and disadvantages

The suitability of a sowing method depends on seed cost, required geometry, field condition, available power, and acceptable precision.

1. Less precise methods:

   • Broadcasting—advantages: High work rate, simple equipment, low initial cost, and suitability for small-seeded pasture, cover, and puddled rice crops.
   • Broadcasting—disadvantages: Random spacing, uneven depth, higher seed rate, difficult inter-row cultivation, and greater exposure to birds or drying.
   • Drilling—advantages: Uniform depth, lower seed rate than broadcasting, orderly rows, improved fertilizer placement, and easier interculture.
   • Drilling—disadvantages: Limited control of within-row spacing, possible tube blockage, calibration requirement, and reduced accuracy under wheel slip.

2. Spaced and precision methods:

   • Dibbling—advantages: Accurate depth and spacing, economical seed use, and suitability for bold seeds.
   • Dibbling—disadvantages: Low field capacity and high labour demand when manually performed.
   • Hill/check-row planting—advantages: Regular hills permit mechanical cultivation; check rows permit cross-cultivation.
   • Hill/check-row planting—disadvantages: Greater complexity, careful alignment, and declining usefulness where herbicides replace cross-cultivation.
   • Precision sowing—advantages: Near-uniform plant population, reduced thinning, efficient use of costly hybrid seed, and consistent crop development.
   • Precision sowing—disadvantages: Higher purchase cost, seed-size grading requirement, sensitive adjustment, and potential vacuum or electronic failure.
   • No-till sowing—advantages: Conserves moisture, reduces erosion, saves fuel and time, and preserves surface residue.
   • No-till sowing—disadvantages: Requires greater opener force, effective residue management, and careful weed and pest control.

IV. Planting and Transplanting Machines — Establishment of propagules and seedlings

A. Planting and transplanting machines: components

Planting machines handle bulky propagules, whereas transplanters place nursery-raised seedlings with their roots or soil plugs intact.

• Common planter units: Frame, hopper or platform, ground wheel, transmission, metering or feeding unit, furrow opener, delivery chute, covering discs, press wheels, depth control, and row markers.
• Potato planter: Uses a tuber hopper, agitator, cup-chain or pick mechanism, furrow opener, delivery chute, fertilizer attachment, and ridging bodies.
• Sugarcane planter: Includes a sett-loading platform or whole-cane feed, cutting device, furrow opener, fertilizer applicator, chemical-treatment system, and covering unit.
• Vegetable transplanter: Uses seedling trays, operator seats or automatic feeders, revolving cups or grippers, furrow openers, press wheels, and often a water tank.
• Rice transplanter: Contains a mat-seedling platform, laterally indexing seedling tray, pickup forks, reciprocating planting arms, float, depth-control mechanism, and row-spacing adjustment.
• Safety and adjustment features: Guards protect chains and cutters; clutch mechanisms prevent overload; sprockets regulate spacing; gauge wheels or floats control depth.

B. Planting and transplanting machines: working

These machines open the soil, meter or receive planting material, place it at controlled intervals, and restore soil around it.

• Potato planting: Cups collect individual seed tubers from the hopper, carry them upward, and release them through a chute into a furrow. Covering discs form a ridge over each row.
• Sugarcane planting: Cane is manually or mechanically fed, cut into setts where required, laid end-to-end or at controlled overlap in furrows, treated, fertilized, and covered.
• Vegetable transplanting: Operators place seedlings into rotating cups, or an automatic feeder extracts plugs. Each cup opens near the furrow bottom, after which press wheels firm soil around the roots.
• Rice transplanting: Pickup forks separate small seedling groups from a mat, move downward and rearward, and insert them into puddled soil. Tray indexing supplies a new strip after each stroke.
• Spacing control: Forward spacing depends on the ratio between ground-wheel travel and the planting-cycle frequency; row spacing depends on the lateral distance between planting units.
• Critical settings: Correct depth, vertical seedling posture, gentle handling, moist root zones, suitable travel speed, and adequate soil firmness reduce mortality and missing hills.

C. Planting and transplanting machines: advantages and disadvantages

Mechanized planting improves capacity and geometric uniformity but demands suitable planting material, field preparation, and skilled operation.

1. Planting machines:

   • Advantages: Save labour, maintain row and plant spacing, place fertilizer simultaneously, cover propagules uniformly, and increase field capacity compared with manual placement.
   • Disadvantages: Bulky or irregular material causes missed or multiple drops; tuber cups and cutters may injure propagules; machines are expensive and require matching seed grades and field conditions.

2. Transplanting machines:

   • Advantages: Reduce peak-season labour, complete planting within the optimum period, maintain regular rows, facilitate mechanical weeding, and provide more uniform depth than hurried manual transplanting.
   • Disadvantages: Require uniformly raised seedlings or mats, careful nursery scheduling, trained operators, and level fields. Plug damage, poor soil contact, incorrect puddling, or excessive speed can increase missing hills and seedling mortality.