Unit 3: Tillage and its implements - Subjective Questions

Primary tillage is the first major soil-working operation performed after harvesting a crop or before preparing land for the next crop. It cuts, loosens, breaks and may invert the soil to a comparatively greater depth.

Main objectives:

• To open and loosen compact soil for better root development.
• To invert the soil and bury weeds, stubbles, crop residues and organic manure.
• To improve soil aeration and water infiltration.
• To break hard layers and reduce soil compaction.
• To expose soil-borne insects, larvae and disease-causing organisms to sunlight and predators.
• To create suitable conditions for subsequent secondary tillage and seedbed preparation.

Primary tillage is generally carried out using mouldboard ploughs, disc ploughs, country ploughs, chisel ploughs or subsoilers.

Advantages:

• Loosens the soil and improves root penetration.
• Buries weeds, crop residues, green manure and farmyard manure.
• Improves soil aeration, infiltration and moisture-storage capacity.
• Helps control certain insects, pests and plant pathogens by exposing them.
• Breaks compact layers and facilitates drainage.
• Prepares the field for effective secondary tillage.

Disadvantages:

• Requires considerable draft, fuel, labour and operating time.
• Excessive tillage can destroy soil structure and reduce organic matter.
• Frequent inversion may expose moist soil and increase evaporation losses.
• Loose soil becomes more susceptible to wind and water erosion.
• Repeated ploughing at the same depth may form a plough pan.
• Heavy implements may compact the subsoil, particularly when the soil is wet.

Common primary tillage implements may be classified as follows:

• Country or indigenous plough: Opens the soil and forms furrows with little or no complete inversion.
• Mouldboard plough: Cuts, lifts, breaks and completely or partially inverts the furrow slice.
• Disc plough: Cuts and turns soil using concave rotating discs; suitable for hard, dry, sticky, stony or trash-covered fields.
• Chisel plough: Loosens compact soil deeply with minimum inversion and leaves much of the residue on the surface.
• Subsoiler: Breaks hardpan or compact subsoil below the normal ploughing depth without substantially inverting the surface soil.
• Reversible plough: Turns all furrow slices in the same direction and avoids the formation of ridges and dead furrows.

The selection depends on soil condition, required depth, residue level, available power and the degree of soil inversion required.

A mouldboard plough cuts, lifts, breaks and turns a furrow slice.

Major components and functions:

• Share: Makes the horizontal cut below the furrow slice.
• Coulter: Makes the vertical cut and separates the furrow slice from unploughed land.
• Mouldboard: Lifts, pulverizes and inverts the cut furrow slice.
• Landside: Bears against the furrow wall and resists the side pressure produced during inversion.
• Frog: Provides the base on which the share, mouldboard and landside are mounted.
• Shin: Forms the leading cutting edge of the mouldboard and protects it from wear.
• Standard, frame and hitch: Support the plough bottom and connect it to the source of power.
• Gauge or depth wheel: Helps control and maintain the working depth.

Working: As the plough advances, the coulter makes a vertical cut and the share makes a horizontal cut. The separated furrow slice moves over the curved mouldboard, where it is lifted, broken and turned to one side.

A disc plough uses individually mounted concave steel discs to cut and turn the soil.

Construction:

• It consists of a strong frame carrying two or more concave discs.
• Each disc rotates independently on a bearing.
• Scrapers remove soil sticking to the disc surface.
• Disc angle and tilt angle are provided to obtain penetration and soil inversion.
• A hitch, furrow wheel, land wheel or gauge wheel may be provided for attachment, stability and depth control.

Working: The inclined and tilted discs penetrate the soil as the plough moves forward. Each rotating disc cuts a furrow slice, lifts it and throws it sideways. Rotation reduces sliding friction and allows the disc to move over minor obstructions.

Suitable conditions:

• Hard and dry soils.
• Sticky soils in which a mouldboard may scour poorly.
• Stony, root-infested or trash-covered land.
• Virgin or uncultivated fields.

A disc plough generally provides less complete inversion and pulverization than a well-adjusted mouldboard plough.

Thus, a mouldboard plough is preferred for clean fields requiring good inversion, whereas a disc plough is preferred for difficult, hard, sticky, stony or trashy conditions.

Chisel plough:

• Uses several rigid or spring-loaded narrow tines.
• Loosens soil below or near normal primary tillage depth.
• Causes limited soil inversion and retains much of the residue on the surface.
• Improves infiltration, root growth and soil aeration while reducing erosion risk.

Subsoiler:

• Uses one or a few heavy, strong shanks fitted with narrow points.
• Operates below the normal ploughing layer to fracture hardpan or compact subsoil.
• Requires high draft because of its greater operating depth.
• Should generally be operated when the subsoil is dry enough to shatter rather than smear.

Difference: A chisel plough loosens a relatively broad portion of the field using several tines and may be used as a regular reduced-inversion tillage implement. A subsoiler is a specialized deep-tillage implement used mainly to break a restrictive compact layer. Neither implement is intended to provide complete soil inversion.

Secondary tillage comprises the shallower soil-working operations performed after primary tillage to produce the final seedbed and prepare the field for sowing or planting.

Objectives:

• To break clods and pulverize the upper soil layer.
• To level and smooth the field surface.
• To destroy young weeds and uproot germinating weed seedlings.
• To mix fertilizers, manure and soil amendments into the surface layer.
• To conserve moisture by creating a shallow soil mulch.
• To compact excessively loose soil and establish good seed-to-soil contact when required.
• To form beds, ridges, furrows or channels for planting and irrigation.
• To obtain suitable tilth for uniform seed placement and emergence.

Harrows, cultivators, plankers, rollers, pulverizers, rotary tillers, ridgers and levellers are commonly used for these operations.

Advantages:

• Produces a fine, level and firm seedbed.
• Breaks clods left after primary tillage.
• Controls small weeds before sowing.
• Mixes fertilizers and amendments uniformly in the surface soil.
• Improves seed placement, seed-to-soil contact and crop emergence.
• Facilitates irrigation, planting and intercultural operations.

Disadvantages:

• Repeated passes increase fuel, labour, time and production cost.
• Excessive pulverization destroys stable soil aggregates.
• Very fine soil is vulnerable to crusting, erosion and surface sealing.
• Additional operations can increase moisture loss through evaporation.
• Implements and tractor traffic may compact moist soil.
• Over-tillage can create an unsuitable powdery seedbed and reduce long-term soil quality.

Therefore, secondary tillage should be limited to the minimum number of operations needed to obtain the required seedbed condition.

Primary tillage creates the basic loosened soil condition, while secondary tillage modifies that condition to produce a seedbed suitable for planting and crop establishment.

Secondary tillage implements can be grouped according to their functions:

• Harrows: Disc, spike-tooth and spring-tooth harrows break clods, stir the surface soil, uproot weeds and mix residues.
• Field cultivators: Use tines or shovels to loosen the upper soil, control weeds and prepare the seedbed.
• Rotary tillers: Use power-driven rotating blades for intensive cutting, mixing and pulverization in a single pass.
• Plankers and levellers: Crush small clods, fill depressions and produce a uniform field surface.
• Rollers and packers: Crush clods and compact loose soil to improve seed-to-soil contact.
• Pulverizers: Combine clod crushing, soil stirring and surface firming.
• Ridgers and bed formers: Form ridges, furrows or raised beds for planting and irrigation.

The implement should be selected according to soil texture, moisture, clod size, crop requirement and desired seedbed condition.

A disc harrow is used for heavier soil working, while spike-tooth and spring-tooth harrows are generally selected for lighter finishing or weed-control operations.

A disc harrow consists of several concave discs mounted on a common shaft to form a gang. The gangs are attached to a frame and arranged in single-action, tandem or offset configurations. Bearings support each gang, while scrapers prevent soil from adhering to the discs. Transport and depth-control wheels may also be provided.

Working:

• The discs rotate as the implement is pulled forward.
• Their concavity and angle cause them to penetrate, cut, lift and throw the soil sideways.
• Opposing gangs balance the side forces and leave a comparatively level surface.

Effect of gang angle:

• Increasing the gang angle generally increases penetration, soil cutting, pulverization and draft requirement.
• Reducing the gang angle decreases penetration and draft and produces lighter soil action.
• Excessive gang angle may cause deep ridging, high draft and unnecessary soil disturbance.

Performance is also affected by disc diameter, disc spacing, implement weight, forward speed and soil moisture.

• Planker: A wooden or metal plank dragged over the field to crush small clods, fill minor depressions, compact loose surface soil and reduce moisture loss.
• Land leveller: Cuts soil from high spots and deposits it in low spots, producing a uniform surface for irrigation, drainage and sowing.
• Roller: Uses cylindrical, ring-type or corrugated elements to crush clods and firm loose soil. It improves seed-to-soil contact but should not be used excessively on wet soil.
• Pulverizer: Uses spring teeth, spikes, rollers or a combination of elements to break clods, stir the surface and produce a fine, firm seedbed.

These implements perform finishing operations. Selection depends on whether the field requires clod crushing, levelling, firming or a combination of these actions.

The following factors should be considered:

• Soil type: Sandy, loamy, clayey, sticky, stony or hard soils require different implements.
• Soil moisture: Soil should be workable; excessively wet soil smears and compacts, while very dry soil increases draft and clod formation.
• Required depth and soil inversion: Deep loosening, shallow stirring and complete inversion require different tools.
• Crop residue and weed condition: Trashy fields require implements that do not clog easily.
• Topography: Slope, terrace width and field shape influence implement size and manoeuvrability.
• Available power: Implement width and draft must match the tractor, power tiller or animal power available.
• Desired seedbed: Fine-seeded crops may require finer tilth than bold-seeded crops.
• Field capacity and cost: Fuel consumption, labour, timeliness and number of passes must be considered.
• Erosion risk: Minimum-disturbance and residue-retaining tools are preferable on erosion-prone land.

Hill agriculture involves steep slopes, narrow terraces, irregular field boundaries and a high risk of soil erosion. Implements used under these conditions should have the following characteristics:

• Light weight: They should be easy to carry, lift and operate on terraces.
• Compact size: Narrow implements are required for small fields and restricted turning space.
• Good manoeuvrability: The operator must be able to turn safely at terrace ends.
• Low power requirement: Human power, animal power and small power tillers are commonly available.
• Stability: Machines should have a low centre of gravity and adequate traction on slopes.
• Adjustability: Working width and depth should suit terraces of different sizes.
• Erosion control: Implements should support contour cultivation and avoid excessive pulverization or downhill soil movement.
• Simple construction: Easy maintenance and local repair are important in remote areas.

Contour-oriented and minimum-disturbance operations are generally preferred to preserve soil and water.

Suitable implements and power sources include:

• Hand tools: Spade, digging fork, khurpi, hand hoe and pickaxe are suitable for very small, steep or inaccessible terraces.
• Animal-drawn implements: Light country ploughs, small mouldboard ploughs, cultivators and levellers can be used where terrace width permits.
• Power tillers: Compact power tillers fitted with rotary tillers, small ploughs, ridgers or cultivators are useful on wider terraces and gentle slopes.
• Light rotary weeders and cultivators: These prepare seedbeds and control weeds with relatively high field efficiency.
• Contour bund formers and small ridgers: These help create erosion-control structures and planting rows along contours.
• Small harvesting and transport attachments: Properly matched attachments can reduce manual effort in accessible hill fields.

Operations should follow the contour as far as practicable. Large, heavy tractors and wide implements are generally unsuitable because of narrow terraces, turning difficulty, slope instability and excessive soil disturbance.

An intercultural operation is a field operation carried out between crop rows after sowing or planting and before harvest. It is performed without causing significant injury to the crop.

Objectives:

• To control weeds that compete for light, water and nutrients.
• To break the surface crust and improve soil aeration.
• To produce a shallow soil mulch and reduce evaporation.
• To improve infiltration of rain or irrigation water.
• To mix side-dressed fertilizers into the soil.
• To perform earthing-up around crop plants.
• To form or maintain ridges and furrows.
• To remove unwanted plants and facilitate crop growth.

The operation must be timely and shallow enough to avoid root pruning, crop burial or excessive moisture loss.

Important intercultural implements include:

• Hand hoe or khurpi: Used for precise weed removal close to plants and in small fields.
• Wheel hoe: A manually pushed implement fitted with sweeps, blades or tines for weeding between rows.
• Animal-drawn cultivator: Uses shovels or sweeps for inter-row weeding in line-sown crops.
• Tractor-mounted row-crop cultivator: Covers several rows and permits depth and row-spacing adjustment for high-capacity cultivation.
• Sweep cultivator: Cuts weed roots below the surface while causing limited soil inversion.
• Duck-foot cultivator: Provides broad shallow cutting for weed control.
• Rotary weeder: Uses rotating blades or tines to uproot and bury weeds and stir the soil.
• Cono weeder: Commonly used between rows of wetland rice under suitable puddled conditions.
• Ridger or earthing-up implement: Moves soil toward plant rows, supports plants and covers fertilizers or weeds.

Selection depends on crop spacing, crop height, weed stage, soil moisture, field size and available power.

Adjustment:

• Match the spacing of cultivator gangs or tines with the crop-row spacing.
• Set a shallow and uniform working depth to avoid crop-root damage.
• Select suitable sweeps, shovels or blades according to weed size and soil condition.
• Maintain an adequate uncultivated protective zone around each crop row.
• Align the hitch and gangs so that the implement tracks centrally between rows.
• Use shields or guards when crops are young to prevent soil from covering them.

Operation:

• Operate when weeds are small and the soil is reasonably dry and friable.
• Travel at a speed that provides effective weed cutting without throwing soil onto plants.
• Keep the implement aligned with rows and lift it before turning at headlands.

Safety:

• Stop the engine and lower the implement before adjustment or cleaning.
• Keep hands and feet away from blades, tines and rotating parts.
• Replace damaged parts and tighten loose fasteners.
• Avoid carrying riders and take special care on slopes and near field boundaries.