Operating Principles of Intercept Tools
Mechanical weeding under the row is an alternative to chemical weeding in viticulture. To optimize its effectiveness, it is necessary to understand the operation of the different available inter-row cultivator tools. This article explains the operating principles of these equipments, detailing the various possible tractor mountings, the retraction control systems, as well as aspects related to the tractor's hydraulic flow.
Tool carriers
Relying on versatility
Successful mechanical weeding depends on the ability to use a variety of tools depending on intervention conditions (soil type, soil condition, development of weeds…). Indeed, flat work with hoe blades may be insufficient. To manage grass around the vines, it is then necessary to use more aggressive tools (sweep blades, rotary tools, ploughs for loosening…). That is why it seems crucial to choose a versatile tool carrier with a range of adaptable accessories.
Different mountings
Mechanical weeding equipment for the vine row can be mounted in different ways on the tractor. There are currently three main types of tool carriers on the market: rear tool carrier frame, front tool carrier frame, or belly-mounted between wheels.
Rear tool carrier frame
This is the most classic mounting. There are short frames that can only hold one tool and long frames that allow combining several. Some frames are exclusively reserved for the use of inter-row cultivators. Some manufacturers offer long frames with a retractable central part. This modular frame allows mechanical weeding of the entire row or keeping the grassed inter-rows and working the vine row.
Belly-mounted between wheels
This mounting offers good visibility of the tools and allows mounting of towed equipment to combine tasks. However, the installation is not easy on all tractors especially for frames equipped with a belly tank. The cost of a belly-mounted between wheels fixing with the hydraulic lift and spacing system is almost identical to that of a rear tool carrier frame, on which other equipment can be mounted for simultaneous use.
Front offset mounting
The front offset mounting fits on the tractor's front weight bracket. This mounting has the advantage of good visibility on the work but maneuvers at the end of the row can be difficult. Moreover, combining front and rear tools requires sufficiently wide rows to allow end-of-row maneuvers. Mounting soil-working tools at the front affects the tractor's balance. Indeed, it unloads the rear axle and may cause traction problems, especially on slopes. It is a rather little-used mounting due to its cost.
Retraction controls
Detection of the vines is ensured by a steel rod called feeler, probe, or vine guide. This metal piece, more or less curved, actuates a torque amplifier, an electric or hydraulic switch.
- Direct control probe: the probe rod controls a hydraulic distributor that operates the retraction cylinder. The system is reliable, inexpensive, and has good sensitivity.
- Electro-distributor controlled probe: the probe acts via a distributor controlled by two electromagnets. This system has finer sensitivity and allows remote control from the cab. The system's complexity makes it more expensive than a direct control probe.
- Orbitrol: this system is based on a component of power steering, the orbitrol. A probe controls the rotation of the servomotor (orbitrol) and allows the tool to retract in front of the vine. This system can be equipped with various accessories to modulate the retraction movement in front of the vines (deformable parallelogram or pivot point).
100% mechanical inter-row cultivators
Low cost, 100% mechanical inter-row cultivators are making a strong comeback on the market because they are simple to adjust. However, they are a bit less responsive than hydraulically retracting inter-row cultivators since their retraction depends on the probe's pressure on the vine. On hard soil,
this pressure becomes very high.
Inter-row cultivators without probe
They are suitable for vines that are homogeneous, on flat and very regular soils. They also allow working on vines with bent trunks. Adjustments are essential to avoid damaging the stocks. On the other hand, when well adjusted, they allow passing very close to the vines and avoid unworked zones. Their use is limited in heterogeneous vineyards and on sloping terrain.
Soil tracking
Inter-row cultivators generally work in right/left pairs. To compensate for differences in slope, some are equipped with a tilt correction system. Two technologies are available: an angular sensor positioned on the probe or a force sensor at a clamp.
Cab control
Almost all inter-row cultivators include cab control. It allows operating the tools from the tractor cab. A set of switches or joystick commands the folding of the tool or its maintenance in the row.
Safety
Despite the safety zone determined by the probe adjustment, it sometimes happens that the inter-row cultivator catches the vine. Inter-row cultivators are thus equipped with mechanical or hydraulic safety.
- Mechanical safety: upon catching, the spring stretches, and when the tension exceeds the set point, the joint bends, the tool carrier folds, and the tool disengages.
- Hydraulic safety: upon catching, the tool exerts a reaction on the cylinder which raises pressure in the circuit. As soon as it reaches the trigger value set on the pressure switch, the relief circuit opens and the cylinder retracts.
Hydraulic flow
Proper use of inter-row cultivators is closely linked to the tractor's nominal hydraulic flow rate. Equipped with gear pumps, their oil flow varies with engine speed. The speed must be adapted according to the tools. The flow will be about 1,600 rpm for using a "blade" type inter-row cultivator. It should be about 2,000 rpm for rotary tools. Some equipment
requiring too high hydraulic flows, it is then preferable to use a hydraulic power pack.
- Simple inter-row cultivators: the required flow is about 15 to 20 l/min for a pair of classic inter-row cultivators, powered by a single or double-acting cylinder. Modern tractors generally have an oil flow that easily covers these needs as well as simultaneous operation of the hydraulic spacing system of the tool carrier frame.
- Rotary inter-row cultivators: the nominal flow needed is around 60 to 70 l/min for driving the rotary tiller motors, opening and closing the inter-row cultivators, and depth control. Most modern tractors can cover these needs. Beware
of overheating issues because the hydraulic reservoir capacity of a specialized tractor is limited. That is why it is recommended to use a hydraulic power pack driven by the tractor's power take-off for rotary inter-row cultivators. This device makes the hydraulic flow independent of engine speed and provides flexibility in work operation.
Sources and references
CUMA Occitanie, 2018, Mechanical weeding of the vine: choosing your inter-row cultivator tools. Available at: https://opera-connaissances.chambres-agriculture.fr/doc_num.php?explnum_id=208768
