Onion Harvester Product

Overview

The self-propelled onion harvester integrates underground bulb extraction, soil separation, foliage topping, and discharge (windrow or tank) into a continuous mobile platform. Onions are harvested after field curing (foliage drying down), requiring gentle handling to avoid bruising and bacterial contamination through skin breaks. The machine is engineered for temperate onion-growing regions (North America, Europe) where harvest occurs in late summer (August–September) when ground moisture is low and soil conditions allow mechanical extraction without excessive compaction.

Modern onion harvesters achieve <3% ground loss and maintain bulb quality suitable for storage (6–12 months at 0–2 °C). The key technical challenge is depth control: undercut too shallow and onions remain in soil; too deep and the share cuts into bulbs, causing decay.

How it works

Soil Loosening and Lifting: The Cutting Share is a hardened steel blade (150 mm wide, 450 mm radius) angled to cut 70 mm below the onion bulb, loosening the soil without shearing the root stub. As the harvester moves forward at 4–8 km/h, the share slides beneath onion rows, undercut soil lifting bulbs upward. The lifting mechanism is spring-suspended on four flexible leaf tine springs that absorb shock when encountering rocks or compacted zones, preventing sudden impact that would jar bulbs and damage skin.

Soil Separation via Web Conveyor: Lifted soil and onions cascade onto the Web Separation Conveyor, a dual-chain conveyor (two parallel roller chains 1000 mm apart, driven at 150 rpm, with cross-bars spaced 150 mm apart) inclined at 30°. As bulbs tumble upward against cross-bars and through the web opening, soil and debris separate and fall through gaps; onions accumulate on the web and continue upward toward the topping unit. Web angle and speed are tuned to achieve 85–95% soil removal while minimizing bulb damage through abrasion.

Foliage Removal: At the top of the web, a Topping Unit cuts dried foliage (any green remaining is removed post-harvest during curing). The rotating disc (400 mm diameter) with reciprocating knife blade cuts at 20–40 mm above the bulb, leaving the protective wrapper leaves intact. Hydraulic height adjustment allows the operator to match varying bulb sizes and foliage residue length within a field.

Discharge and Collection: Topped onions are directed downward via a discharge chute into either a windrow (for later hand collection and bagging) or an optional 600 L onboard tank for semi-mechanical loading. Windrow discharge allows rapid harvesting (8–10 hectares per day) with post-harvest labor for bagging; tank discharge suits smaller operations or where mechanical loading infrastructure (conveyor, truck-mounted blower) is available.

Hydraulic System: A 50 cc/rev variable-displacement axial piston pump (load-sensing, 210 bar rated) supplies pressurized fluid to the rear steering cylinder (65 mm bore, 320 mm stroke) and the topper height-adjustment cylinder (50 mm bore, single-acting). The pump is driven directly by the diesel engine; proportional directional valve allows the operator to modulate steering from the cab via proportional joystick.

Electrical Integration: A 70 A three-phase alternator supplies 24 V DC to independent motor circuits: web conveyor motor (5.5 kW, proportional soft-start for smooth engagement), topping motor (2.2 kW), and (if equipped) tank discharge auger motor (1.5 kW). Soft-start contactors limit inrush current, protecting alternator from transient voltage dips when multiple motors start simultaneously.

Chassis and Mobility: The self-propelled chassis uses 13.6/48 agricultural radial tires on dual axles with 2.0:1 reduction gearing. Front-wheel drive (via bevel differential and reduction gearbox) and leaf spring suspension (22 kN/m rate) with hydraulic dampers provide traction on slopes up to 14° and smooth ride over field obstacles. Rear axle is non-driven but hydraulically steered, providing proportional cornering control with 7 m turning radius.

Bulb Quality and Storage: Onions are sensitive to mechanical damage; bruising creates stress cracks in the papery outer skins, allowing pathogenic fungi (Fusarium, Botrytis) to penetrate and cause storage rot. Mechanical harvesters maintain 98–99% of bulbs free from bruising and cuts when soil conditions are optimal (20–30% moisture) and forward speed is moderate (4–6 km/h). Bulbs harvested by mechanical means achieve 5–7 month storage life at 0 °C / 70% RH, compared to 8–12 months for hand-dug onions in premium storage conditions.

Harvest Operations

Typical day: harvester operates 8–10 hours, covering 1.0–1.6 hectares depending on field size, soil type, and discharge method. For windrow harvest, two workers follow the machine, bagging onions into 25 kg mesh sacks; throughput is 4–5 hectares per person-day. For tank discharge, 1–2 trucks with 3–4 tonne capacity rotate collection; auger discharge fills a truck in 20–25 minutes.

Moisture Management: Onions must be field-cured after harvest (foliage drying to ground level) before storage. Curing time is 2–4 weeks at ambient temperature (15–25 °C, low humidity); inadequate curing traps moisture under outer skins, promoting rot. Mechanical harvesters leave onions in low windrows to facilitate drying, typically not requiring re-handling between harvest and curing completion.

Maintenance: The web conveyor chain requires regular tension checks (deflection <12 mm mid-span); chain replacement after 150–200 operating hours is typical. Spray-clean the bulb contact surfaces (web chains, discharge chute) weekly to prevent soil and organic residue buildup that would reduce separation efficiency and promote premature wear.