Row spacing for retained stubble systems in Tasmania

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  • Canola produced similar levels of dry matter for grazing on wide or narrow rows.
  • Wide row spacing increased paddock scale yield by 25 per cent compared to narrow row.
  • Grazing reduced grain yield of canola on either spacing, but not significantly.

The challenges of retaining stubble in the high rainfall zone are significant owing to the higher yields, and subsequent stubble loads, typical of the region. Adapting or adopting seeding machinery with row spacings greater than 25cm presents growers with an opportunity to overcome challenges that come with retaining stubble such as blockages at seeding. However, there is some reticence around wider crop rows with previous research indicating a negative impact on yield when crop rows are increased.

In medium to low rainfall zones, there has been a great deal of work done looking at row spacings and the effect varying spacings has on establishment and yield in most grain crops. Generally, the message has been that wider rows reduce yields in canola grown only for grain.  However, the increased incidence of planting winter canola for grazing and grain means that previous research may not hold true in the high stubble loads of irrigated crops in Tasmania.

For weed competition, canopy closure is important, and it is generally accepted that under high stubble loads narrower spacing leads to more even establishment, higher plant populations, faster canopy closure and reduced weed growth. With dual purpose winter canola, the grazing of crops has meant that canopy closure is not achieved until much later into the spring and row spacing may now play an important part in establishing crops that produce more early feed, recover better from grazing and create a plant that is easier to harvest.

How does row spacing influence grazing and grain yield of hybrid winter canola under irrigation in Tasmania?

To answer this question, two trials were established on heavy wheat stubble (>16t/ha) at Cressy in Tasmania to test the response of winter canola variety Hyola 970CL to wide versus narrow row spacings.

The narrow row treatment was 26cm sown with a SeedHawk drill and the wide row was created by blocking two out of three boots of the seeder, creating a 78cm row spacing. Such a large spacing is highly unusual, but was done here for the sake of the comparison. It would be more usual to block one seeder row and create a ‘double row’ pattern with a gap of 52cm every second row.

Dry matter (feed) yield

The first dry matter cuts were taken prior to first grazing on April 14 when plants were at eight-leaf stage, and prior to a second grazing on May 19. Heavy grazed plots were mown down to remove all leaf matter. Lightly grazed plots left approximately one third of leaves on the lower stem.

Sowing canola on very wide spacings resulted in lower dry matter production under grazing pressure, but ungrazed plots produced similar amounts of vegetative matter under either spacing. It is worth noting that plant survival after grazing was excellent with 83 per cent plant survival under narrow rows and 92 per cent under wide rows.

Table 1: Total dry matter (t/ha) produced in nil grazed plots.

Cut 1 April 14

Cut 2 May 19

Total DM

Wide 80cm

0.83

2.15

2.98

Narrow 27cm

0.91

2.18

3.09

Increased yield

Hybrid canola sown on 78cm row spacing produced high yield with low plant numbers. See Table 1. There was significant shattering/bird damage across all plots (estimated at 10 per cent yield loss) which would have brought plot harvest results more closely in line with the paddock average.

The canola on 26cm row spacings was accidentally harvested with the surrounding paddock before plot harvests could be completed. Discussion with the harvest operator revealed that in the paddock the narrow row spacing was averaging 4.4t/ha and wide row spacing 5.5t/ha.

The difference between yields was not statistically significant at P=0.05.

Table 2: Grazing intensity effect on yield (t/ha) in wide rows.

Grazing intensity

Yield (t/ha)

Nil

5.416a

Light

4.647a

Heavy

4.606a

Reduced establishment costs

Canola row-spacing research (Harries, M et al; 20131) undertaken in Western Australia showed wide row spacing by low seed rate was the highest yielding treatment in three out of five replicated trials. The researchers theorised that there was potential to reduce both seed and fertiliser input at seeding to reduce costs associated with vigorous hybrid varieties, and the current Tasmanian trial supports this.

Blocking out rows on the Seedhawk drill reduced plant population on the wide row spacing – wide (25 plants/m2) versus narrow (59.5 plant/m2) row. This reduction was unexpected, but may have been due to more seeds being sown per metre row thus increasing competition between seedlings. Achieving greater yield from the reduced plant population shows there is potential to reduce sowing rates without impacting yield.

Under grazing systems, now common in Tasmanian grain growing areas, wide row spacing may allow for better inter-row weed control once sheep have been removed. Canola sown on wide rows achieved canopy closure post-grazing in a similar time frame to narrow rows (six days later), and although this does give weeds a few more days to establish, the shading of the canopy should retard further growth, similar to standard row spacing.

Figure 1. Canola sown on 27cm spacing at September 8, 2015.

Figure 1. Canola sown on 27cm spacing at September 8, 2015.

Figure 2. Canola sown on 80cm spacings as at September 14, 2015.

Figure 2. Canola sown on 80cm spacings as at September 14, 2015.

Challenges and further research

Not all growers will be able to modify equipment to test wider row spacings in their system.

This work was undertaken in one of the driest winter and spring seasons on record in Tasmania. Further row spacing work needs to be undertaken to ascertain if these results can be repeated. The effect of wide row spacing on incidence of sclerotinia and blackleg also needs to be tested, as disease levels were very low in 2015.

References

Harries M. & Seymour M. et. al. (2015), GRDC Update papers, ‘Wide Row Canola why bother; a summary of a series of small plot and farmer trials and farmer experiences’, GRDC Project No. DAW00277. Available at: https://www.grdc.com.au/Research-and-Development/GRDC-Update-Papers/2015/02/Wide-row-canola-why-bother

Pritchard F., et al (2010), Over the Bar with Better Canola Agronomy: 2010. Available at: http://www.nvtonline.com.au/wp-content/uploads/2013/03/Crop-Guide-Canola-Over-the-Bar-with-Better-Canola-Agronomy.pdf.

By Heather Cosgriff
SFS Tasmanian project and trials manager
E: hcosgriff@sfs.org.au

GRDCLogoStacked_TM_CMYKThis research is being conducted by BCG as part of the GRDC Maintaining profitable farming systems with retained stubble initiative (project BWD00024 ‘Maintaining profitable farming systems with retained stubble in Victoria and Tasmania’).

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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About BCG

Birchip Cropping Group Inc. (BCG) is a not-for-profit agricultural research and extension organisation led by farmers in the Victorian Wimmera and Mallee.
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One Response to Row spacing for retained stubble systems in Tasmania

  1. Pingback: Row spacings in a retained stubble system | The stubble project: Victoria and Tasmania

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