Last reviewed 1 Oct 2026 · 9 min read
Harvesting — meaning and requirements
Harvesting is the cutting, collection and (for grain crops) separation of the economic part of the crop at the right maturity. It is a time-critical, labour-intensive operation: delay increases shattering, lodging and weather damage, while mechanical harvesting reduces labour and loss.
Requirements of a harvesting machine: clean cutting at the desired height, low grain loss and damage, handling crops of varying condition (lodged, wet, tall), high capacity, operator safety, low cost.
Cutting mechanisms
| Mechanism | Description | Use |
|---|---|---|
| Reciprocating knife (sickle bar) | A toothed knife moves back and forth against stationary guards (fingers); a shearing cut | Reapers, mowers, combine headers (the most common) |
| Double-knife (opposed) cutter | Two knives moving in opposite directions | High speed, no guards; less vibration |
| Rotary (disc or drum) cutter | High-speed rotating blades (or discs) cut by impact without a counter-edge | Rotary mowers, disc mowers (hay, fodder); handle thick growth at high speed |
| Flail cutter | Free-swinging flails (knives) on a horizontal rotor | Forage harvesters, stalk shredders, cutting heavy residue |
| Serrated blade | Toothed hand sickle or machine blade | Cereals (serrated sickle is better than a plain one) |
| Shear (scissor) cutter | Two blades shear the stem | Pruning, hedge trimming |
| Chopper (cylinder with knives) | Cuts the crop into short lengths | Forage harvesters, silage cutters |
Reciprocating cutter-bar details
- Stroke length about 76 mm (3 inch); speed 800–1200 strokes/min; section (blade) pitch 76 mm with guard spacing equal to the pitch (standard configuration).
- Cutting action: the knife section moves across the guard, and the edge of the section against the ledger plate shears the stem; sharpness and clearance are critical.
- Cutting height: adjustable (stubble height 10–15 cm for cereals; lower for forage).
Harvesting tools and machines for cereals
| Machine | Function and use |
|---|---|
| Sickle (hand tool) | Serrated sickle: about 0.01–0.02 ha/h per person; high labour (60–80 man-hours/ha for wheat) |
| Reaper (cutter-windrower) | Walk-behind or tractor-mounted; cuts and lays the crop in a windrow (or swath) for manual collection and bundling; 0.2–0.5 ha/h |
| Reaper-binder | Cuts and ties the crop into bundles (sheaves) with twine; 0.3–0.5 ha/h; used for wheat, rice, millets |
| Mower | Cuts grass, forage or hay crops (cutter-bar, rotary, disc, flail) |
| Windrower / swather | Cuts and lays crops in windrows for field drying (e.g., canola, hay); self-propelled |
| Self-propelled vertical conveyor reaper (VCR) | Cuts and conveys the crop vertically for laying in a windrow; popular for wheat, rice and gram in India |
| Stripper header | Combs the grain from the standing crop, leaving the straw standing |
| Combine harvester | Cuts, threshes, separates and cleans in one machine |
Combine harvester
DefinitionThe combine
A combine harvester performs cutting, feeding, threshing, separating, cleaning and grain collection in a single pass, delivering clean grain into a tank and leaving the straw either windrowed or chopped. It replaces reaping, bundling, carting, stacking, threshing and winnowing.
Types
| Type | Description |
|---|---|
| Tractor-drawn (pull-type) | PTO-driven; pulled by a tractor; small farms; cheaper |
| Tractor-mounted | Fixed on a tractor (cuts costs but limits the tractor's other use) |
| Self-propelled (conventional) | Own engine, cab and drive; the common type for large farms; capacity 0.5–1.5 ha/h in wheat |
| Axial-flow (rotary) combine | A long rotor threshes and separates using centrifugal force; higher capacity, handles tough or damp crops, gentle on the grain (more common in modern machines) |
| Hybrid | Conventional cylinder with a rotary separator |
| Track combines (crawler) and paddy combines | Rubber tracks for soft, wet paddy soil |
Functional parts and operations
FormulaFlow of the crop through a conventional combine
- Header (platform) — divider points separate the crop; reel (bats/tines) sweeps the crop to the cutter bar; cutter bar (reciprocating knife) cuts it; auger (platform auger) moves the cut crop to the centre.
- Feeder house (inclined conveyor) — chain conveyor carries the crop to the threshing unit; stone trap protects it.
- Threshing unit — cylinder (drum) and concave — rasp-bar or spike-tooth cylinder (rotating at 600–1200 rpm; peripheral speed 15–30 m/s) rubs the crop against the concave; the grain and chaff fall through the concave (threshing by impact and rubbing).
- Beater (straw beater) — strips the straw from the cylinder to the straw walkers.
- Straw walkers (or rotary separator) — oscillating, serrated steps that shake out the remaining grain from the straw and carry the straw to the rear.
- Cleaning shoe — grain pan, chaffer (upper sieve), sieve (lower), and a fan (air blast) — separates grain from chaff by size and air; tailings (unthreshed heads) return to the cylinder.
- Grain elevator and auger — carry the clean grain to the grain tank (bunker).
- Unloading auger — empties the tank into a trailer.
- Straw chopper / spreader — chops and spreads the residue (or windrows it for baling).
Adjustments
| Adjustment | Effect |
|---|---|
| Cylinder (drum) speed | Higher — more complete threshing but grain damage and more chaff; lower — less damage but unthreshed heads |
| Concave clearance | Closer — better threshing, more damage; wider — less damage |
| Fan speed and sieve opening | Control cleanliness and loss with the chaff |
| Reel speed and position | About 1.25–1.5 × forward speed; reel ahead of the cutter bar and low enough to hold the crop |
| Forward speed | Higher speed raises the feed rate and losses; typical 2–5 km/h |
| Cutting height | Stubble height |
Losses in combining
| Loss | Cause |
|---|---|
| Header (pre-harvest) loss | Shattering by the reel, lodged crop missed, cutter bar loss |
| Cylinder (threshing) loss | Unthreshed grain on straw — cylinder too slow or concave too wide |
| Separation loss | Grain carried over with the straw from the walkers (overload) |
| Cleaning (shoe) loss | Grain blown out with the chaff — fan too fast or sieve overloaded |
| Grain damage | Cracked or broken grain — cylinder too fast, concave too close, grain too dry |
Total loss should be about 1–2 % of yield (standard: < 2–3 %); a loss monitor or a drop-cloth test (e.g. counting grains per m²) estimates it.
Worked ExampleExample — combine capacity
A self-propelled combine with a cutter bar of 3.0 m works at 3.0 km/h with a field efficiency of 72 %.
ha/h; . For a wheat yield of 4.5 t/ha, the grain throughput is t/h. In a ten-hour day the combine harvests about 6.5 ha, replacing roughly 500 man-hours of manual harvesting and threshing.
Crop and machine conditions
- Moisture content of grain at combining: wheat 14–20 %, paddy 18–24 % (to reduce shattering) — dry to safe storage moisture (12–14 %).
- Straw management: combine residues (rice, wheat) — chopped and spread, baled (straw balers, straw reapers), or used with Happy Seeder; burning is harmful and is regulated.
- Custom hiring of combines is common because of the high cost (₹ 20–40 lakh and above — a hypothetical range).