Seeder Tracking and Guidance for Precise Row Sowing
March 3, 2017
By Jack Desbiolles, Agricultural Machinery R&D Centre, University of South Australia
AG CONTRACTOR & LARGE SCALE FARMER March/April 2017 Issue 99
A seeder that maintains precise pass-to-pass accuracy regardless of terrain opens the door for guided sowing relative to existing stubble rows. Accurately sowing in relation to previous stubble rows can be critically important to successfully establish crops in low or uneven moisture situations.
In high residue loads, inter-row sowing into standing residue with tine seeders can decrease or eliminate residue clumping and interference over the seed rows.
With disc seeders, inter-rowing sowing controls residue hairpinning, especially in combination with residue managers. It also ensures good soil-to-seed contact. In both cases, inter-row sowing significantly improves the efficiency of crop establishment, enabling lower seed rates, and higher speeds at similar pre-emergence herbicide safety and efficacy. At the same time, the intact stubble can effectively shelter seedlings against wind damage and soil moisture loss. Inter-row sowing also reduces take-all and crown rot disease pressure, and makes it easier to harvest pulse crops.
Alternatively, in non-wetting soils and low fertility sands it is often advantageous to place the seed in proximity to the previous stubble row rather than in the middle of the inter-row because more moisture and nutrients are present in an existing furrow compared to the inter-row zone. This approach results in drastically improved germination, a longer sowing window, more even crop development, and increased grain yield. While near-row (or edge-row) seeding and centre-row (or on-row) seeding can both be used to generate these benefits, edge row seeding is preferred to retain stubble integrity with tine seeders, and to minimize hairpinning with disk seeders. Overall, better results are achieved with a side banding configuration.
With accurate implement guidance, the contiguous row sowing within a dedicated permanent seed zone may over time create improved fertility strips. A research project funded by Grains Research Development Council (GRDC) will evaluate this technique over the next four years. While there are a number of guidance technologies with various capabilities, implement tracking stability is the starting point. This article provides an overview of relevant considerations on the subject.
Seeder Tracking Stability
Accurate sub-inch RTK guidance of the tractor and stable implement tracking are both necessary to achieve guided row sowing. Accurate tractor guidance increasingly uses sophisticated ‘terrain compensation’ software to accurately steer the tractor hitch along the guidance path. Different towed seeder bars have different tracking abilities, so accurate auto-steering of the tractor alone may not always be sufficient. The stability of the seeder is influenced by the forces applied onto the bar in relation to the tractor pulling force. The forces applied on the seeder bar include:
- forces at the implement hitch, including tractor pull;
- the weight of the seeder bar;
- tyre reactions, including rolling resistance;
- opener draft, penetration and side forces;
- drag forces from a tow-behind air-cart.
An air-seeder fitted with a ProTrakker steerable draw-bar hitch for active implement guidance.
An imbalance in horizontal (draft, side) forces creates drift as the implement’s centre of draft tries to line-up with the tractor centre of pull. This drift can be random in response to hanging soil conditions or working depths. Or it can be systematic, when the implement is set incorrectly or its weight causes the implement to crab downhill when operating along a side slope. Random drift is a significant issue when trying to accurately inter-row sow, while systematic drift may sometimes be managed by following the same seeding pathway, season after season.
Implement drift is measured by the extent of skew angle in relation to the travel direction. While at work, forces from the implement’s wheels and the furrow openers create ‘restoring’ forces that stabilize the bar and limit drift within a maximum skew angle. Successful guided row sowing requires the bar to travel straight. With large multi-rank bars even a small skew angle, such as on a side slope, quickly becomes incompatible with guided row sowing because it creates variable seed furrow spacings.
A small skew angle with very compact bars (one or two ranks) is generally acceptable and guid-ed row sowing can be achieved by following the same seeding pathway, season after season.
Design Principles For Good Tracking
A balanced bar design is the first requirement for a good tracking stability. This includes symmetrical layouts of both openers and wheels, and a uni-form distribution of the seeder bar weight, including over the wing sections.
Where the wheels are positioned relative to the tines can improve or worsen tracking. For example, working depths will be affected if they ride into the fur-row or over soil throw ridges during skewing. Wide tires placed on a walking beam are typically least sensitive to the above. A longer A-frame gives an advantage by stabilizing drift at smaller skew angles. A common rule of thumb is that the draw-bar length should be half the implement width to give sufficient restoring power to rig-id frame wheels.
Constant tillage depth across the bar is critical. It is best achieved by openers that follow ground contours. This is especially important on wider, less-stable bars and undulating land.A poorly set-up bar or inadequate floatation in soft soils can create a constant force imbalance that causes systematic drift to the left or right. You can check the extent of systematic drift by sowing up and back on flat land and checking for alternate ‘closed’ and ‘open’ spaces between adjacent passes.
The use of a pointer and dial kit (a pointer fitted to the tractor over a dial fitted to the implement) can provide a reference to assess and/or video the extent of skewing movements while at work. Rigid wheels, either singles or as a walking beam on the bar, act as rudders and provide restoring forces. Their ‘restoring power’ is improved by a greater loading weight, a larger wheel skid angle, and a greater distance behind the tractor’s towing point. Larger skid angles can be obtained by positively steering frame wheels to keep the bar on its intended path. This can be done manually or automated with sensor or GPS input (see below).
To maximize the stability of a tine seeder bar, avoid steep narrow openers because they absorb some of the bar weight by generating an upward soil reaction, especially when dry seed-ing in hard soils. Conversely, shallow rake angle points (less than 60 deg.) with optimum wear at the cutting edge can both add to the existing frame weight and decrease the seeder draught requirement.Avoid castor wheels because they take on the weight of the frame but do not help restore tracking.
A fully mounted air seeder box placed near the rearmost supporting (rigid) wheels of the seeder bar and openers placed close to the towing tractor can improve tracking. A tow-between air-cart adds another ‘link’ to the tow-chain, and places the implement further behind the tractor. On side slopes, this can increase the extent of implement drift down-slope, especially when the air-cart is near-empty.
On the other hand, a tow-be-hind air-cart acts as a damp-ing force on the flat. It tends to reduce the amount and suddenness of random implement drift by decreasing the impact of a force imbalance. However, when operating on a side slope, the tow-behind cart drag force increases the downslope-pull on the seeder which increases its skew angle. Twin axle air-carts with steerable wheels can minimize this impact relative to single axle carts.
Working at slower speeds can improve guided row sowing accuracy. In practice, inter-row sowing is easier to achieve than near-row sowing because of the larger margins of error, especially at row spacings of 300mm or more. Edge-row sowing is suitable to narrow row spacing (180-200mm) with accurate guidance and stable tracking.
A common source of implement drift is the tendency for the openers to return to last year’s row when inter-row sowing, especially in harder soils. Force imbalances push the openers away from the harder inter-row zone into the weaker furrow side. This problem is more significant with lighter weight seeders, and stability can be improved with a higher load on the seeder wheels and the use of steering hitches guiding the implement.
Guiding implements to targeted pathways gives the most accurate implement control. Implement guidance falls into two categories: Passive guidance: These systems combine GPS data from mounted receivers on both the tractor and implement to auto-steer the tractor such that the implement always remains on the intended guidance path.
This is the cheapest option but requires the tractor to move on and off track to keep the implement on the targeted path.It is best suited to gradual and systematic drift so it is combined with a stable seeder bar to minimize transient and sudden random drift. Example technologies include John Deere IGuide, Trimble TrueGuide.
Active implement guidance: These systems guide the implement independently of the tractor. Active implement guidance is more expensive but the extra accuracy may be warranted to improve cropping returns.
This technology is based on dedicated ‘auto-steering’ systems for the implement, of which there are two main types:
A) Hitch correction is where the tractor draw-bar or the implement hitch tongue is hydraulically adjusted side-to-side to guide the implement. A system controller reacts to GPS receiver position data from the implement itself or to data from a stubble row or furrow/ridge tracking sensor fitted to the implement.
This approach adjusts implement position up to a maximum offset but without correct-ing any skew angle. With large offset drift (such as on side slope), this approach may not always be sufficient. Example technologies include SunCo Farm Equipment AcuraTrak guidance system, John Deere hitch-based iSteer, MBW ProTrakker Guidance Systems (GPS, Side-Hill Sensor and SonicTrakk), Seed Hawk SBR technology, SeedMaster SmartHitch and AgriParts I-till.
B) An implement steering kit actively directs the implement frame over the guidance path using steerable wheels or disc blades to generate a corrective force. Their action is con-trolled by GPS position data from both the implement and the tractor.
This approach corrects an implement skew angle in order to track squarely behind the tractor over a common guidance path. Provided they achieve sufficient penetration, piloted disc blades can generate larger restoring forces than steerable, surface running wheels. Example technologies include John Deere wheel-kit iSteer, Orthman Agriculture Shad-ow Tracker and Tracker IV.
Contact Jack Desbiolles for further information on Jack.firstname.lastname@example.org or phone 08 8302 3946.
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