On and edge-row sowing can significantly improve crop establishment on non-wetting soils, especially for canola. Sowing on or very near to last year’s crop row lets the crop access old root channels. Water infiltrates more easily into these ‘preferred pathways’ than the surrounding repellent soil, giving the crop a better chance of establishing.
Non-wetting inter-rows harvest moisture into those rows, including from summer rains, further increasing moisture at seeding. Wetter furrows can make residual fertiliser more accessible as nutrients will be more available and microbial activity will be higher where there is more moisture. Wetter furrows also help reduce repellence by making conditions friendlier for wax-degrading bacteria and, on the downside, on and edge-row sowing can increase the risk of root disease with cereals on cereals.
On-row sowing works well where stubble is short, brittle and not too dense. High stubble loads and stronger stubble can cause issues such as ‘hair-pinning’ (where the stubble is bent and pushed into the row, reducing seed-soil contact) and seed tubes blockages. This causes poor seed placement, reduced seed-soil contact and lower plant establishment.
Edge-row sowing – accurately sowing within a few centimetres of last year’s rows – achieves a similar result to on-row sowing but without the problems caused by stubble.
Seeder bar guidance
On and edge-row sowing need seeder bar guidance. The most rudimentary method is to rely on tynes and the seeder bar gravitating to the path of least resistance – last year’s rows. As this relies on ‘feel’ while driving, it is the least accurate option. Using Real Time Kinematic (RTK) auto-steer tractor guidance might help reduce seeder bar drift.
Automatic seeder bar guidance reduces or eliminates drift in and out of last year’s rows, in turn reducing operator error. There are two types of seeder bar guidance: passive and active.
With a passive system (for example, John Deere AutoTrac™), the tractor moves to keep the seeder bar on the desired guidance path. Passive guidance is cheaper than active guidance but does not reduce seeder bar drift as much. The constant tractor movement to correct seeder bar drift can increase wear and tear on the tractor. In controlled-traffic farming (CTF) systems, in trying to keep the seeder bar on the correct path the tractor sometimes steers off the tramlines and into the rows.
Active guidance, commonly called mechanical steering, moves the seeder bar independently of the tractor. This level of precision is critical for edge-row sowing where there is more chance of sowing into non-wetting soil. Active guidance is also preferred if using machinery that can make the seeder bar drift more, such as an articulated tractor, wheeled tractors (instead of tracks) and if the seeder bar has a short drawbar.
Tools for active guidance include an adjustable hitch system, a stubble sensor paddle and steerable drawbar, and steerable wheel axles. All active systems need a second auto-steer system on the seeder bar. The main active guidance systems used in Western Australia are:
- ProTrakkerTM – a hydraulically controlled guidance hitch with a GPS receiver fitted on the tractor and on the seeder bar. The hitch will constantly make minor adjustments to keep the bar on the row;
- TrueTrackerTM – an implement steering system that keeps the hitch mounted and drawn implements on the same path as the tractor; and
- iTill® – a steerable drawbar that can be fitted to any tractor-seeder combination. A row tracking unit (sensor paddle) and camera allow the driver to fine-tune seed placement and monitor soil throw and ground speed.
One downside of guidance systems is that they can be time-consuming, tedious to set up and are largely brand-specific, although this is changing with generic systems such as Homburg Holland’s SmartSTEER® system. Costs are variable depending on the additional equipment you need and can include an adjustable hitch system or stubble paddle plus steerable drawbar, tractor auto-steer, additional receiver, additional RTK subscription, harnesses and cabling, guidance controller, upgrade of tractor screen and (for tow between set-ups) a hitch on the cart.
Starting from scratch, the total cost could be at least $30,000, so it is important to analyse its cost-effectiveness. Data cautiously suggests yield increases of 5 to 10 per cent with on and edge-row sowing. Used across 2000 hectares of a 2.5 tonne/ha cereal crop, it can add $60,000 to $120,000 in revenue.
Specialists can help set up guidance systems. They are relatively low-cost compared with the benefits they achieve and the hassles they remove.
Setting AB lines
For on and edge-row sowing to work, you need to be able to repeat the sowing pattern, year after year. This requires a single set of ‘foundation’ or ‘zero’ lines saved in the autosteer system. Work out the preferred run line direction and distance from fence lines to set up and save the lines.
The foundation lines should be as straight as possible. Some growers want to wait for wet sowing to set up foundation lines for fear of poor establishment in year one. However, if dry sowing is a common occurrence it could take a few seasons for the right conditions to occur. At some point it is best to just start on-row sowing.
With the iTill®, harvesting in the foundation year on an angle to the lines (for example, 10 degrees) will help in the second year by reducing problems caused by stubble from wheel tracks and burnt chaff lines/windrows, allowing the sensor paddle (which is not mounted for use until year two) to have a continuous line of stubble to follow from then on.
Seeder bar and tractor set-up
The ideal seeder bar has equally spaced tynes. Seeder bars with a central tyne will need an odd number of tynes in total so there is the same number on either side of the central tyne. Seeder bars without a central tyne need an even number of tynes. A central tyne is not critical but does make set-up easier and some growers report it better anchors the bar to the foundation lines.
Mismatched bars with unevenly spaced tynes, or more tynes on one side, do not track as straight and increase the workload of, or defeat, the automated steering system. If you use a mismatched bar you will need to seed in the same direction every year – something that is best avoided if possible when managing logistics and labour at seeding.
Steep, narrow openers can make the bar drift more, especially when dry seeding in hard soils. Castor wheels can also make sowing straight harder. A tow-behind air cart can reduce drift when driving on flat ground, but increase drift on slopes (Desboilles 2017). Many air carts do not have the axle bolted or welded in absolutely square, which can cause the bar to drift. Check axle alignment and straighten if required. Twin axle air-carts with steerable wheels can have fewer issues compared with single axle carts.
For edge-row sowing, the tractor needs to be set up to drive exactly on line zero with the drawbar in the centre of the tractor. To calibrate, drop something (for example, a rod) through the drawbar and drive up and back to check line zero is the same in both directions.
If the rod has made two lines in the soil, the tractor and GPS antenna settings need to be changed; usually the tractor driving settings are altered to ‘trick’ the GPS antenna. Test again and adjust until the rod leaves only one line in the soil after driving up and back. Getting guidance right is harder with articulated tractors.
This process then needs to be repeated on the seeder bar, making sure a tyne (or, even better, every tyne) runs on the same line both up and back. If there is not a central tyne, at least two tynes will need to be checked.
The lead tyne should run close to the stubble. A side band system can help get the seed closer to the stubble, but makes the run in the opposite direction difficult as the bar must be nudged at the end of every run.
Paired-row sowing is a common solution. It can get very close in and under the previous year’s stubble without balling the stubble forward and upsetting the seedling establishment along the row.
With paired-row sowing there is always one side of the paired row in the right spot while using a single annual nudge line, and some growers are ‘getting by’ with this compromise. Sacrificing one side of the paired row into the inter-row is deemed a non-issue on low-cost seed crops but becomes an issue when seeding high-value hybrids.
Experience suggests that direct-drill sowing points that sow the seed into the wall with soil flowing over the point are better than closer plate systems that drag non-wetting soil back into the furrow.
Advanced edge-row sowing
Growers experienced with edge-row sowing are:
- Sowing on the foundation lines every second year because there are fewer problems sowing into second-year stubble;
- Nudging to the left or right in alternate years, depending on what phase of the rotation the paddock is in, especially canola because;
- Sowing canola on the north or west side (the direction from which most of their rain comes) of the previous year’s cereal stubble is showing better establishment, possibly because of better water harvesting from standing stubble and/or more sun/temperature;
- Planning for the canola phase when nudging their rows; for example, if sowing canola in 2022, the 2021 cereal is nudged to the south or east;
- Adjusting the nudge distance depending upon stubble condition and length. Longer straw needs a wider offset. A 20-millimetre nudge can be achieved with about 150mm stubble and 40mm with about 200mm stubble without disturbing the bulk of the stubble;
- Sowing within five centimetres of the centre of the previous year’s furrow on a narrow 12 to 16mm knife-point system. The closer the better;
- Using 45mm closers on the seeder bar, which spreads seed from zero to 40mm from the previous year’s row, close enough to get into the moisture zone of last year’s row.
This article was produced as part of the GRDC ‘Maintain the longevity of soils constraints investments and increase grower adoption through extension – western region’ investment (PLT1909-001SAX). This project is extending practical findings to grain growers from the five-year Soil Constraints – West suite of projects, conducted by the Western Australian Department of Primary Industries and Regional Development, with GRDC investment.
Desboilles J. 2017. “Seeder Tracking & Guidance for Precise Planting”. Precision Farming Dealer. Published online 16 March, 2017.