Inter-row sowing

stubble guideline interrow sowing JS

GRDC stubble management guideline No. 11 – Inter-row sowing (click on the image to access this guideline)

The practice of inter-row sowing, whereby crops are sown between the previous year’s stubble rows, is compatible with stubble retention as it minimises trash flow issues at seeding and improves crop emergence.

Key points

  • Accurate tractor guidance and stable implement tracking are key issues
  • Improved handling of heavy stubbles and enhanced harvestability of pulse crops such as lentils
  • Other benefits include timeliness of sowing, improved water infiltration and conservation, increased ability to retain stubble, reduced soil erosion, labor and input savings, lower take-all disease pressure(as next year’s crop is not growing in in previous crops row).
  • Implement tyne layout is important to avoid stubble blockages when off-tracking. Tine under-frame clearance of at least 500mm is recommended.

Overview

Seeding between rows, better known as inter-row sowing has been widely adopted by growers in the low to mid rainfall zones of the Victorian Mallee and Wimmera. The practice is compatible with stubble retention as it minimises trash flow issues at sowing. Efficiency gains also result through precise seed placement with less herbicide throw into crop rows, reduced tractor driver fatigue and a number of other agronomic benefits (McCallum Agribusiness Consulting, 2008).

The inter-row system

Inter-row sowing generally refers to crops sown between the previous year’s crop stubble rows. An RTK (real time kinematic) auto-steer guidance system is typically used, which offers ± 2cm accuracy. Repeatable straight line accuracy is important to ensure the seeding row remains in the intended stubble inter-row.

Less accurate guidance systems (sub-foot guidance accuracy, eg. from ±10 to ±30cm) are not generally suitable for inter-row sowing in winter crop environments. It has been suggested that success rate for inter-row seeding varies in practice according to the tractor guidance accuracy and the implement tracking stability as follows:

  • 90% for ±2 cm RTK system using own base station
  • 70% for sub-foot auto-steer (±10 to ±30 cm)
  • 50% by eye using permanent wheel tracks

Consequently, successful inter-row sowing requires a plan that takes into account: machinery set up, the accuracy and reliability of the RTK guidance system and residue management when retaining standing stubble and sowing with the same row spacing in the same direction each year (Gooden, D. 6th Australian Controlled Traffic Conference, 2008, McCallum Agribusiness Consulting, 2008.)

Inter-row sowing is easier to implement at wider row spacings (greater than 22cm, or 9 inch). It is generally unsuitable for systems with row spacing less than this but does very well when rows are set 25-30cm (10-12 inch) apart (GRDC Stubble Management Fact Sheet, March 2011).

Seeder set-up and blockages

Blockages of sowing implements is one of the major perceived impediments to inter row sowing. Modification to the profile and tyne layout can reduce stubble clumping and blockages. Bar clearance and tyne layout have a stronger influence on the machine’s ability to cope with heavy stubble loads.

Stubble management GRDC factsheet ‘Strategies to manage winter crop stubbles without reaching for the matches’ 2011 suggests:

  • A straight rather than a curved shank will avoid residue building up at one point.
  • Shanks with a rounded cross section have improved residue flow.
  • Vertical or slightly backward leaning shanks promote a constant off-balancing effect on residue, reducing build up.
  • Sudden changes of shape in shank profile delays residue flow and promotes clumping. High C shapes, where the upper part of the C is above the stubble flow work well.
  • Stream-lined designs with recessed bolt heads for point mounts also reduce residue catching.
  • Existing curved shank tynes can be improved by retrofitting stubble tubes to make the face of the shank round and more vertical.
  • Long knife-point openers can increase the effective vertical clearance of short tynes, but their break out rating needs to sustain the greater lever arm effect.
  • Modifications according to stubble load:
    • Inter-tyne spacing of 55-60cm is adequate in 3.5 to 4.5t/ha wheat stubble cut at 35-40cm. Where inter-tyne spacing is the horizontal distance between any two seeding tyne assemblies measured in any direction.
    • For a taller stubble of 45-55cm, inter-tyne spacings need to increase to 80cm for standing stubble.

When purchasing or retrofitting a tyned seeder bar:

  • Maximise the inter-tyne spacing by tyne layout pattern, row spacing, rank spacing and rank number.
  • Match inter-tyne spacing to residue length. Minimum inter-tyne spacing should be twice the residue length.
  • Create a tyne layout that minimises the number of clump interactions with following tynes. Rear of the seeder is most prone to stubble build up and press wheels to close to the back rank of tynes can be another build up point.
  • Position wheels to maximize resude flow. Place tynes in front of wheels.
  • Sowing into dryer stubbles is easier.
  • Use lower reaching narrow points and shallower tillage depths to maximize the vertical clearance.

Machinery and technology messages:

  1. An accurate tractor guidance system (RTK) with a reliable guidance signal from season to season (constant base-station location), a stored paddock AB line data, and a suitable nudging factor or implement hitch offset are paramount.
  2. In the best case scenario, tractor guidance is enough to achieve suitable implement guidance when implement tracking is stable.
  3. In practice, implement tracking is variable and influenced by a number of seeder design and terrain factors. Similar sowing patterns should be followed each year to help manage tracking issues.
  4. Skews of angle means difference between rows (row-spacing is not altered). This makes it harder to inter-row sowing in the following year.
  5. When implement tracking is not suitable, additional implement guidance technology is required.
  6. Passive implement guidance refers to the tractor’s auto steering and sophisticated software that can guide the tractor on an alternative track to keep the implement on the intended guidance path.
  7. Active implement guidance is when implements are actively steered to remain on the intended guidance path, in addition to, and independently of, tractor guidance. Examples include steerable tractor and implement hitches, and steerable implement wheel or disc kits. Sensors used to detect implement position include stubble row tracking or implement differential guidance positioning system (DGPS) position data. Implement design factors influencing tracking. For example, large spaced between gangs (rows of tynes) = longer implement and therefore more chance for it to go off course.
  8. Implement tyne layout is important to avoid stubble blockages when off-tracking. Tine under-frame clearance of at least 500mm is recommended.
  9. Residue managers can be attached to push surface crop residue away from path of tynes (Whitlock. A)
  10. In-frame/between bar clearance of at least 650mm is required for residue handling equipment.

Discs versus tynes

Disc seeders offer less soil disturbance, enable more surface residue retention and faster sowing opportunities (Ashworth et al., 2010).

In trial work, triple discs (higher disturbance) achieved improved mechanical incorporation and showed no crop damage from better meeting the positional selectivity requirements of pre-emergent herbicides due to soil throw features similar to knife points. However, greater variability in crop damage occurred with single disc seeders (lower disturbance).

Single discs with the addition of effective row cleaners achieve better crop safety, by removing the herbicide contaminated surface soil and residue, ahead of placing seeds, so that it effectively controls the risk of herbicide and residue contact. Some single disc seeders are designed to achieve soil scuffing from the seed guard, which can also contribute to greater crop safety, at the cost of extra wear and draft.

Bentleg openers

Farm machinery research at UniSA (Jack Desbiolles et al. 2015) is investigating the benefits of bentleg tine openers. These novel openers offer potential for high speed, low soil throw tyne seeding by controlling soil throw and soil inversion.

Field experiments showed that bentleg openers, when compared with knife point openers: provided low draft requirements due to low rake angle on the leading foot; dramatically reduced lateral soil throw; reduced furrow spill over by up to 90%; and the majority of soil remained unmixed and in the furrow.

The bentleg opener maintained low soil disturbance characteristics at speeds of up to 16km/hr.

Further work is being investigated with seed and fertiliser banding boot designs for accurate seed placement, suitable residue handling and reliable crop establishment.

Implications of stubble load for inter row sowing

Challenges at seeding and with crop performance can occur when the stubble load is greater than 3-4t/ha of dry matter (GRDC Stubble Management Fact Sheet, March 2011).

Approximately 100 g/m2 of dry stubble equals 1t/ha of crop residue.

Wheat stubble dry matter proportion can be 1.3 to 2.8 times the grain yield, although this ratio varies with the season, time of sowing, soil type and variety.

The following calculation could be used to determine stubble dry matter:

3t/ha grain yield x 1.5 = 4.5t/ha stubble dry matter

Inter row sowing with retained stubble

Management of stubble starts at harvest with even spreading of residue and appropriate cutting height. Straw lengths of 20cm or less can allow tyne machines to work effectively with stubble loads of up to 5t/ha of stubble dry matter (GRDC Stubble Management Fact Sheet, March 2011).

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The stubble project – maintaining profitable farming systems in Victoria and Tasmania with retained stubble (project number BWD00024) is funded by the GRDC.

Disclaimer: Any recommendations, suggestions or opinions contained in this publication do not necessarily represent the policy or views of the Birchip Cropping Group (BCG) or the Grains Research and Development Corporation (GRDC). No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. BCG and GRDC and contributors to these guidelines may identify products by proprietary or trade names to help readers identify particular types of products. We do not endorse or recommend the products of any manufacturer referred to. Other products may perform as well as or better than those specifically referred to. BCG and GRDC will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information in this publication. 
Stubble project overview: This guideline has been developed for BCG Farming Systems Group as part of the Maintaining Profitable Farming Systems with Retained Stubble initiative, funded by the Grains Research and Development Corporation (GRDC). The initiative involves farming systems groups in Victoria, South Australia, southern and central New South Wales and Tasmania collaborating with research organisation’s and agribusiness to explore and address issues for growers that impact the profitability of cropping systems with stubble, including pests, diseases, weeds, nutrition and the physical aspects of sowing and establishing crops in heavy residues.
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4 Responses to Inter-row sowing

  1. Pingback: Row spacing for retained stubble systems in the Wimmera and Mallee | The stubble project: Victoria and Tasmania

  2. Pingback: Research | The stubble project: Victoria and Tasmania

  3. Pingback: Desired stubble characteristics for the Wimmera and Mallee | The stubble project: Victoria and Tasmania

  4. Pingback: Sowing into stubble: seeder set-up and selection | The stubble project: Victoria and Tasmania

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