Unit 3: Tillage and its implements

I. Foundations of Tillage — Soil Manipulation for Crop Production

Tillage is the mechanical manipulation of soil with tools and implements to create conditions suitable for seed germination, crop establishment and plant growth. It changes soil structure, surface condition, aeration, moisture movement and weed population. The required intensity depends on soil texture, moisture, crop, slope, residue cover and farming system.

A. Defining Characteristics

Tillage operations must produce a useful seedbed without causing unnecessary soil degradation or energy expenditure.

• Tilth: Tilth is the physical condition of soil in relation to seed germination, root growth, aeration and water movement. Good tilth contains stable aggregates rather than massive clods or excessively pulverized particles.
• Primary and secondary sequence: Primary tillage opens and loosens the soil, whereas secondary tillage refines the seedbed and prepares the field for sowing.
• Soil-working action: Implements may cut, lift, invert, pulverize, mix, compact or level soil. A mouldboard plough, for example, cuts and inverts a furrow slice; a disc harrow mainly cuts and mixes it.
• Working depth: Primary implements commonly work deeper than secondary implements. Typical primary depth is about 15-30 cm, while many secondary operations are performed within the upper 5-15 cm.
• Soil moisture condition: Tillage is most effective near a friable moisture condition. Wet clay smears and compacts, while very dry soil requires greater draft and forms hard clods.
• Draft: Draft is the horizontal force required to pull an implement, commonly expressed in newtons or kilonewtons.

Draft = Specific draft x Cross-sectional area of soil cut

• Specific draft: Force required per unit cross-sectional area, usually expressed in N/cm² or kN/m².
• Area of soil cut: Approximately working width multiplied by working depth.
  • Conservation requirement: On sloping or erosion-prone land, residue retention, contour operation and minimum soil disturbance are preferred over repeated, slope-aligned tillage.

II. Primary Tillage — Initial Opening and Loosening of Soil

Primary tillage is the first major soil-working operation after harvest or before crop establishment. It penetrates relatively deeply, breaks compact soil and may invert or mix the surface layer.

A. Primary tillage: objectives

The main objective of primary tillage is to open the soil and create a workable root zone for the succeeding crop.

• Soil loosening: Breaks hard or compact layers to improve root penetration. A chisel plough may loosen soil 20-35 cm deep without complete inversion.
• Furrow-slice manipulation: Cuts, lifts and, when required, turns the soil. A mouldboard plough buries surface material by inverting the furrow slice.
• Weed control: Uproots, cuts or buries weeds and volunteer plants. Deep burial is particularly effective against emerged annual weeds.
• Residue and manure incorporation: Mixes crop residues, farmyard manure and green manure into the soil, increasing contact with decomposing microorganisms.
• Pest exposure: Exposes soil-inhabiting insects, pupae and disease-bearing residues to sunlight, desiccation and predators.
• Improved infiltration and aeration: Increases large pore spaces temporarily, allowing rainfall or irrigation water and oxygen to enter the cultivated layer.
• Preparation for later operations: Produces furrows or rough clods that can subsequently be reduced by harrowing, cultivating and planking.
• Moisture management: Summer ploughing can increase rainfall intake, while timely opening of heavy soil may improve drainage.

B. Primary tillage: advantages and disadvantages

Primary tillage can correct restrictive soil conditions, but excessive or poorly timed ploughing damages structure and raises production costs.

1. Advantages:

   • Root-zone development: Deep loosening reduces mechanical resistance, enabling roots to explore a larger soil volume for water and nutrients.
   • Effective incorporation: A mouldboard or disc plough can bury weeds, manure and residues more thoroughly than shallow implements.
   • Compaction treatment: Chisel ploughs and subsoilers break dense layers. A subsoiler may work at approximately 35-60 cm where a plough pan exists.
   • Improved field condition: Rough ploughing exposes large clods to alternate wetting, drying and weathering, especially in heavy soils.
   • Crop sanitation: Burial or exposure of infected residue may interrupt some pest and disease cycles.

2. Disadvantages:

   • High energy requirement: Greater depth and soil volume increase draft, fuel consumption, wheel slip and operating cost.
   • Moisture loss: Turning and loosening moist soil exposes a larger surface area to evaporation.
   • Erosion risk: Bare, finely exposed soil is vulnerable to wind and water erosion, particularly when furrows run downhill.
   • Structural degradation: Repeated tillage at the same depth may form a compact plough pan below the worked layer.
   • Organic-matter decline: Intensive aeration accelerates oxidation of soil organic carbon.
   • Unsuitable wet-soil effects: Operations in wet soil cause smearing, puddling and subsurface compaction.

C. Primary tillage implements

Primary tillage implements are designed for relatively deep penetration and substantial cutting, loosening or inversion of soil.

• Country or indigenous plough: A simple animal-drawn implement with a wooden body and iron share. It opens a narrow furrow but provides limited inversion and requires repeated passes.
• Mouldboard plough: Consists principally of the share, mouldboard, landside, frog, coulter and hitch or frame.
  • Share: Makes the horizontal cut beneath the furrow slice.
  • Coulter: Makes the vertical cut.
  • Mouldboard: Lifts, breaks and turns the slice.
  • Landside: Resists lateral pressure against the furrow wall.
• Disc plough: Uses concave, inclined steel discs that roll through the soil. It performs well in hard, dry, sticky, stony or root-infested fields where a mouldboard may clog or suffer impact damage.
• Chisel plough: Uses strong, narrow tines to shatter compact soil with little inversion. Residue remains comparatively close to the surface, improving erosion protection.
• Subsoiler: A heavy, narrow shank operating below normal ploughing depth to fracture a hardpan. It should be used only where field observation or soil-penetration resistance confirms a restrictive layer.
• Reversible plough: Carries right- and left-hand bottoms so soil can be turned consistently in one direction. It avoids dead furrows and back furrows and is useful on slopes.
• Rotary plough or rotavator: Power-driven blades cut and mix soil. It can combine major soil breaking with pulverization, although repeated intensive use may over-pulverize the surface.

III. Secondary Tillage — Seedbed Refinement and Surface Management

Secondary tillage consists of shallower operations performed after primary tillage to reduce clods, control young weeds and create the final conditions required for sowing and irrigation.

A. Secondary tillage: objectives

The main objective of secondary tillage is to convert rough-ploughed soil into a firm, level and suitably fine seedbed.

• Clod reduction: Breaks large clods into aggregates small enough to provide seed-soil contact without turning the soil into erosion-prone powder.
• Surface levelling: Removes ridges and depressions, promoting uniform sowing depth and even distribution of irrigation water.
• Weed destruction: Cuts or uproots newly emerged weeds before planting or between preparatory operations.
• Moisture conservation: A shallow soil mulch interrupts capillary continuity and may reduce evaporation from moist subsurface soil.
• Fertilizer mixing: Incorporates broadcast fertilizers into the upper soil layer; incorporation depth should match the crop and nutrient-management requirement.
• Seedbed firming: Presses loose soil around the seed zone. Small seeds generally need a finer, firmer seedbed than large seeds such as maize.
• Field layout: Forms beds, ridges, furrows, channels and bunds needed for sowing, drainage or irrigation.
• Residue distribution: Spreads and mixes remaining residues so they do not obstruct seed drills or cause uneven crop emergence.

B. Secondary tillage: advantages and disadvantages

Secondary tillage improves sowing conditions, but each additional pass adds traffic, cost and risk of excessive pulverization.

1. Advantages:

   • Uniform crop establishment: Levelling and clod breaking allow openers to maintain more consistent seed depth.
   • Better seed-soil contact: Light compaction around seeds supports imbibition, the initial uptake of water needed for germination.
   • Pre-sowing weed control: Shallow cultivation destroys weed seedlings without herbicide use.
   • Efficient irrigation: A level field reduces water ponding, runoff and non-uniform application.
   • Combined operations: A cultivator fitted with a levelling board can loosen, weed and level in one pass.

2. Disadvantages:

   • Over-pulverization: Repeated harrowing destroys stable aggregates, encouraging crusting and erosion after rainfall.
   • Traffic compaction: Tractor wheels compact soil, especially when multiple passes are made under moist conditions.
   • Moisture and fuel loss: Every operation exposes moist soil and consumes fuel, labour and field time.
   • Delayed sowing: Excessive seedbed preparation may postpone planting beyond the optimum date.
   • Weed regeneration: Cutting perennial weeds into pieces can spread species capable of vegetative propagation.
   • Depth limitation: Secondary tools cannot effectively correct a deep hardpan or severe subsoil compaction.

C. Secondary tillage implements

Secondary tillage implements work mainly in the surface layer and are selected according to clod size, residue level and required seedbed condition.

• Disc harrow: Uses gangs of concave discs set at a gang angle. It cuts clods, weeds and residues and mixes the upper soil layer; greater gang angle generally increases penetration and soil movement.
• Spike-tooth harrow: Carries rigid pointed teeth for shallow stirring, light clod breaking, residue spreading and final seedbed finishing.
• Spring-tooth harrow: Uses flexible tines that vibrate and pass around stones or roots. It suits relatively hard or trashy fields.
• Cultivator: A frame-mounted group of shovels, sweeps or tines used for shallow loosening and weed control. Field cultivators commonly follow ploughing.
• Rotavator: A power-take-off-driven rotor with L-shaped or similar blades. Rotor speed and forward speed determine pulverization and bite length.
• Plank or leveller: A wooden or steel member dragged over the field to crush small clods, fill depressions and lightly compact the seedbed.
• Roller and clod crusher: Crushes clods and firms loose soil. Smooth rollers compact the surface, while corrugated or Cambridge-type rollers leave a textured finish.
• Ridger and bed former: Shapes ridges, furrows or raised beds for row crops, irrigation and drainage.

IV. Specialized Field Implements — Slopes and Crop-Row Management

Specialized implements adapt tillage to steep, narrow or terraced land and permit weed control or soil manipulation after the crop has been planted.

A. Implements for hill agriculture

Hill implements must be light, stable and manoeuvrable while minimizing downhill soil movement and erosion.

• Reversible or turn-wrest plough: Turns the furrow slice toward the uphill side during both travel directions, reducing progressive soil displacement downhill.
• Lightweight mouldboard plough: Animal-drawn or power-tiller-mounted models suit small terraces where full-sized tractors cannot turn safely.
• Power tiller with rotary attachment: Provides compact mechanization for narrow plots. Cage wheels or suitable lugged tyres improve traction in soft soil.
• Contour cultivator: Works approximately across the slope along contour lines, leaving small barriers that slow runoff and increase infiltration.
• Hand hoe and spade: Permit precise soil working around stones, terrace edges and irregular boundaries inaccessible to machines.
• Wheel hoe: A manually pushed tool fitted with sweeps, hoes or small tines for shallow cultivation on relatively uniform terraces.
• Mini tiller: A low-mass engine-powered rotary unit used in orchards, vegetable terraces and confined hill fields.
• Safety and conservation: Implements should have a low centre of gravity, effective braking and limited width. Operations must avoid unstable terrace edges and saturated slopes.

B. Implements for intercultural operations

Intercultural implements operate between crop rows after sowing to control weeds, aerate soil, conserve moisture and support the crop.

• Hand hoe: Uses a blade attached to a handle for cutting weeds and loosening soil close to plants. It is accurate but labour-intensive.
• Wheel hoe: Increases human work rate through a wheel-guided frame carrying sweeps, blades or tines; it is suitable where row spacing permits movement.
• Animal-drawn blade harrow: A shallow horizontal blade cuts weeds below the surface in widely spaced crops.
• Row-crop cultivator: Tractor-mounted gangs of sweeps or shovels cultivate spaces between rows. Adjustable gangs must correspond to the crop’s row spacing.
• Sweep cultivator: Broad V-shaped sweeps cut weed roots with minimal soil inversion, helping retain surface moisture.
• Rotary weeder: Rotating tines uproot or bury weeds and aerate the surface. Guarding prevents excessive soil or plant damage.
• Cono weeder: Two truncated conical rotors disturb puddled soil between line-planted rice rows, incorporating weeds and improving aeration.
• Finger or brush weeder: Flexible fingers or brushes remove small weeds near crop rows with less injury than rigid blades.
• Ridger or earthing-up implement: Moves soil toward plant bases in crops such as potato, sugarcane and maize, supporting stems, covering fertilizers and improving drainage.
• Operating control: Interculture should be shallow enough to avoid crop-root pruning. Guidance shields, gauge wheels and accurate row alignment reduce crop damage.