Select a seeding system for your soil
Author: Rebecca Barr | Date: 07 Mar 2016
Choosing a seeding system suited to growers’ specific needs can have significant benefits in crop performance.
University of South Australia agricultural research engineer Jack Desbiolles has spent years studying the impacts of seeding systems on crop performance under different soil types and residues.
“Getting the seeder set-up right is critical for rapid seed germination, uniform crop emergence and good early vigour,” he said. “Due to the diverse nature of soils and climatic conditions there is no one-size-fits-all solution.”
Through the Agricultural Machinery Research Design Centre (AMRDC) at UniSA, Dr Desbiolles has conducted GRDC, SAGIT and DAFF-funded research into optimising seeder set-up in no-till systems.
Paired row systems for variable soil types
“One of the challenges Mallee growers encounter at seeding time is the inability to maintain a consistent and accurate seeding depth across all soil types in the paddock,” Dr Desbiolles said.
“As a result crop establishment is often variable with crops sown too shallow on the stony soils and too deep on the sandy hills, which significantly impacts crop emergence, erosion risks and ultimately crop profitability.”
Research by the Minnipa Agricultural Centre during 2007-09 found that both tyne and disc seeders could be used effectively in stony soils as long as the settings were optimised; getting the settings wrong, such as too shallow seeding depth in dry conditions, reduced establishment by up to 40 per cent.
Seeding system comparison trials conducted at Murrayville in the Victorian Mallee during 2014 identified that paired row systems gave the highest and most consistent wheat crop establishment across three soil types (Figure 2), after very good soil moisture conditions at sowing.
Seeding systems were compared to the district technology of a simple chisel tine with knife point, rubber seed boot and narrow press wheel. In terms of emergence, the benefit of paired row systems ranged from 15 per cent on the mid-slope and sand hill, to 20 per cent on stony soils. Under a dry season finish, the paired row systems gave 0.05-0.15 t/ha improvement in wheat yield, with the largest benefit on the stony flat.
A more advanced seeding system featuring a gauge wheel regulated seed delivery independent from the furrow opener also performed better in the stony flat, with 17 percent higher crop emergence and 0.1 t/ha additional grain yield.
Dr Desbiolles says the paired row benefits measured in the Murrayville trial correlate well with previous research work on the benefits of higher seedbed utilisation (SBU), which is the proportion of the row spacing occupied by the crop. SBU can be increased either by reducing row spacing or increasing lateral seed spread on each row, such as with paired-row and spreader boot systems.
“Paired row and spreader boot systems allow higher SBU with the same row spacing, which improves grain yield potential, reduces fertiliser toxicity risks and enhances crop competition with weeds,” he said.
According to Dr Desbiolles, however, this does not mean that paired row systems are always an obvious solution.
“These systems have potential disadvantages, such as reduced seed outlet size which may not be suited to larger seeds or high seed rates, higher risk of blockages in sticky conditions and higher soil disturbance with a potential increased risk of pre-emergence herbicide damage, depending on the design,” he said.
Sandy soil systems
“Sandy soils present the highest risk of the soil drying out quickly and reducing germination,” Dr Desbiolles said.
Recent research work suggests the following strategies should be considered for more reliable crop establishment in sandy soils, where marginal moisture conditions are encountered:
- Place seed in contact with undisturbed soil moisture. This requires side banding or paired row banding able to place seeds on undisturbed ledges, or single shoot systems able to band seeds at furrow tilling depth. Deep furrow sowing capabilities may be required to reach moisture, or else growers can use low rake angle openers, low speed and compact seed banding systems to delve deeper.
- Minimise the fertiliser applied with seeds to control fertiliser toxicity, and use a double shoot system, with side or side plus vertical separation.
It is important to note that a lack of sub-seed disturbance may increase the severity of rhizoctonia damage on young seedlings, and the use of liquid banding technology to combine in-furrow trace element application and fungicide protection at sowing may be necessary as part of a mitigating strategy.
Seed-fertiliser separation is particularly important in small seeded crops like canola for successful germination on sandy soils.
“Obtaining high SBU is important to manage fertiliser toxicity risks,” Dr Desbiolles said. “In marginal moisture conditions, including non-wetting soils, it may be necessary to have full separation between seed and basal fertiliser, preferably banded at depth to maintain the maximum crop establishment potential.”
Trials in the SA Mallee in the early 2000s found that 70 per cent SBU tyne sowing was able to significantly minimise establishment losses in canola, reporting no grain yield loss at harvest, compared to up to 45 per cent yield loss to fertiliser toxicity at 15-20 per cent SBU.
Successful use of high SBU systems requires careful selection of equipment to suit growers’ conditions.
“When selecting for a higher SBU system, there are many factors to consider including single or double shoot, distinct split-rows or a wide band sowing, integrated opener design or wing attachment for an existing opener, and fertiliser placement relative to the seed zone,” Dr Desbiolles said.
“In order to better establish crops in marginal soil moisture, it is important to select a design able to place seeds on undisturbed soil moisture, being aware that some systems will instead place seeds into furrow backfill, at greater risk of diluted moisture and potentially pre-emergent herbicide damage.”
Non-wetting soil challenges
Non-wetting sands present specific challenges leading to slow and patchy seedling emergence. Trials in non-wetting sand at Moorlands in South Australia in 2015 found that crop establishment under a single-shoot narrow point system significantly reduced due to fertiliser toxicity, from 82 per cent emergence to 58 per cent (in a system with 25cm row spacing and fertiliser rates of 13 kg/ha nitrogen, 9kg/ha phosphorus and 12 kg/ha sulphur). Crop emergence rate was further reduced down to 34 per cent with a low soil disturbance, single disc system, due to the combined effect of fertiliser toxicity and lack of surface soil clearing.
“The best treatment, reaching over 90 percent emergence, in the Moorlands trial was obtained by adding a shallow operating scooping share ahead of a triple disc seeding system to clear away the top 3-4cm of soil into the inter-row zone and assist with placing seeds into moist soil,” Dr Desbiolles said.
“This scoop design used as a proof-of-concept required low operating speed (5km/h) to avoid ridging. Paddock-ready ‘scoop’ solutions would need testing but could include concepts based on modified front coulters or knife points to emphasise an effective surface soil clearing at common operating speeds.”
“Such targeted furrow disturbance is a useful concept to apply in non-wetting sands and may also more generally be useful in dry sandy soil conditions when seeking to place seeds into moisture and controlling furrow backfill.”
On and near row sowing in non-wetting sand can promote access to greater moisture available in existing stubble rows.
This approach was successfully demonstrated in recent Western Australian research and also validated in the SA Mallee during 2015. CSIRO trials in 2015 also showed a significant reduction in brome grass germination associated with this technique.
Successful near-row sowing is more challenging to achieve than inter-row sowing, and requires a side banding seeding system and RTK tractor plus implement auto steer. Inter-row sowing should, however, be used where soils are evenly wetted and moisture is not limiting, to access other benefits.
Managing herbicide toxicity
Tyne seeders are reliably safest at ensuring crop safety, as long as the following guidelines are adhered to:
- Control speed to ensure no soil throw reaches adjacent furrows and the majority of herbicide is concentrated over the inter-row zone
- Ensure seeds are placed at sufficient depth with clean backfill to achieve adequate physical separation between crop seed and herbicide (known as ‘positional selectivity’).
- Create stable furrows to limit the risk of contaminated soils backfilling over time, and leaching of soluble herbicides into the seed zone.
Care must be taken with disc seeders when using pre-emergent herbicides. Trials at Roseworthy in the SA lower-north in 2012/13 showed that trifluralin significantly reduced wheat emergence with single discs, by up to 50 per cent. However, using triple discs or applying Sakura® caused no damage.
The greater safety with triple disc systems is explained by their soil throw features being akin to a knife point system. Further, the inclusion of residue managers fitted ahead of the single disc openers significantly reduced crop damage. Growers should always follow herbicide labels to assess suitability for disc seeders.
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Useful Seeding Resources
- Mallee Sustainable Farming Seeder Set-up Guide (pdf download)
- GRDC Update paper: Seeding systems and pre emergence herbicides
GRDC Project Code MSF00003