Stubble retention in the high rainfall zone 2017

James Manson (SFS)SFS_FINAL_Logo

Key Messages

  • Retained stubble reduced canola establishment and increased pest damage.
  • Using an Arricks wheel at sowing improved canola establishment, especially under retained stubble.
  • Baiting for slugs is an important consideration for growing canola in retained stubble.
  • Spraying setup has the potential to significantly improve herbicide penetration in retained stubble systems.


Retaining stubble in cropping systems can increase surface water infiltration, reduce wind and rain erosion and increase soil organic matter. However, the typical practice up until recently has been to burn stubble because it can also decrease crop emergence, increase pest and disease pressure and block seeders in the following season. Now, with growing dissatisfaction by growers and the public of the environmental costs of burning stubble, there is increasing pressure to find alternatives to the practice. This requires creative solutions so that crop residues can be retained without compromising farm profitability. The GRDC funded project “Maintaining profitable farming systems with retained stubble in Victoria and Tasmania” (BWD00024), of which SFS is a project partner, has been making progress towards these solutions since it began in 2015.

Work by SFS in 2015 showed that disc seeders handle stubble better than tynes. Using a disk as opposed to a tyne was also slightly more profitable due to savings on sowing time, harvest efficiency and fuel costs. However, other important practices include spacing tynes further apart and using Real Time Kinematic (RTK) guidance for successful inter-row sowing. The trials in 2015 were successfully established in 6.6 t/ha cereal stubbles. Pest levels were low this year so any possible differences between treatments due to the presence of pests were not found.

In 2016, trials and demonstrations were conducted on canola sown into cereal stubbles. Stubble reduced canola emergence. It was shown that canola seed should be treated with Cosmos, or it should be incorporated by sowing, and isolated from urea. Dry conditions meant that using a disc resulted in lower canola emergence compared to tynes, in contrast to 2015. Baits containing 7.5 kg/ha Metarex and 2.5 kg/ha Mesurol reduced plant damage from 56% to 40%, illustrating the importance of pest control for stubble retention in the HRZ.

This report presents data from a trial and two demonstrations conducted by SFS in 2017. These build on previous findings and will contribute to the larger project from multiple locations.


On-farm trial, Streatham

A paddock-scale trial was established in Streatham in 2016 as a split-plot design. There were three blocks of stubble management: grazed, burnt or retained. Within each block there were combinations of two stubble heights (15 or 30 cm) and sowing equipment (Arricks wheel or no wheel) with four replicates each. Each bed was 12 m wide and 300 m long (100 m per block). On 28 April 2017 Hyola 650 TT canola, treated with Cosmos, was sown with 80 kg MAP. Crop establishment counts were conducted on 18 May 2017. Plant damage by pests was scored visually on the same date.

Baiting demonstration, Streatham

A baiting demonstration was attached to the on-farm trial in Streatham. Metarex (7.5 kg/ha) or Mesurol (2 kg/ha) was applied in tiles along the length of the trial under the three stubble management blocks. Crop establishment and plant damage was also assessed on 18 May 2017.

Herbicide demonstration, Cressy

A crop-walk demonstration was conducted on canola stubble in Cressy in March 2017. The aim was to illustrate the effect of retained stubble on herbicide efficacy and the importance of sprayer set up. Four spraying set-ups were used on three stubble heights (see below). Water-sensitive paper was used to illustrate the degree of herbicide penetration into the stubble under different heights and setups. The area covered by herbicide was calculated digitally.

sfs 2017 t1

Table 1. Factors used in herbicide demonstration. 12 treatments total.

Results and Discussion

On-farm trial, Streatham

Crop establishment was affected by stubble management, the Arricks wheel, and the interaction of management x Arricks wheel x stubble height (see Table 2, data ranked from high to low establishment). Establishment was greatest after burning, followed by grazing then retained stubble. Using an Arricks wheel also increased plant establishment. It would be expected that the order of crop establishment should consistently follow the pattern burn > graze > retain and Arricks wheel > no Arricks wheel. However, using an Arricks wheel with retained stubble had a greater establishment than grazed stubble sown without an Arricks wheel.

The results follow the typical pattern where retained stubble reduces canola emergence. It is interesting that sowing with an Arricks wheel improved establishment. Using an Arricks wheel with retained stubble may improve conditions for establishment to levels similar to grazing stubble without sowing with an Arricks wheel, but this would have to be repeated in another trial to be a reliable finding because the management x Arricks wheel interaction was not quite signficiant (p = 0.07). Stubble height had an inconsistent effect on establishment.

sfs 2017 t2

Table 2. The effect of stubble management, Arricks wheel and stubble height on crop establishment in a canola crop.

Similarly, burning stubble resulted in the least pest damage to new crop plants. Grazing achieved a similar level of plant damage to new plants, whereas retained stubble resulted in the greatest damage. For this measurement, 15cm stubble treatments had less damage than 30 cm stubble. The interaction between stubble management and stubble height was also significant. Under grazed and retained stubble conditions, a 15 cm stubble height resulted in less pest damage. However, under burnt stubble 30 cm was better than 15 cm. This could be because in the cases of grazed and retained stubble, 15 cm provides less habitat for pests. For the burned treatment, however, 30 cm stubble provides more fuel for the burn resulting in improved pest control. In contrast to crop establishment, not using an Arricks wheel was better than using one. However, given that the difference between Arricks wheel treatments was only 2.9% for a visual score it is unlikely that this represents a meaningful effect on pest damage.

sfs 2017 t3

Table 3. The effect of stubble management, Arricks wheel and stubble height on plant damage in a canola crop.

Baiting demonstration, Streatham

The effect of stubble management on crop establishment and plant damage in the baiting demonstration (Tables 4 and 5) followed the same pattern as the nearby on-farm trial. Baiting treatments were similar in crop establishment, but Mesurol 2 kg/ha appears to have provided greater protection from pests than Metarex 7.5 kg/ha. This data is based on multiple, unreplicated assessments and cannot be tested with descriptive statistics, but may be useful for informing future hypotheses. There was no interaction between stubble management and bait.

sfs 2017 t4

Table 4. The effect of stubble management and baiting on crop establishment.

sfs 2017 t5

Table 5. The effect of stubble management and baiting on plant damage.


Herbicide demonstration, Cressy

The effect of stubble height on herbicide penetration was surprisingly small (see Figure 1). Small and inconsistent differences in the paper are visible but are not clarified by the calculation of area covered by spray. A smaller spacing did not affect penetration. Extending the nozzles into the stubble increased penetration in one of three cards, but this treatment was more variable. The only treatment that was substantially more penetrating was a 25 cm spacing with an extended nozzle and 80° nozzle angles. Coverage of the water-sensitive paper in this treatment was twice as great as the other treatments. Further research could test this demonstration in a replicated trial. It would be necessary to compare every combination of factors, since it is not clear from this trial if 80° nozzles would be as effective with 50 cm spacing.

sfs 2017 f2

Figure 1. Effect of nozzle spacing, extension and angle on herbicide penetration into standing stubble.


In the trial from 2017 retained stubble reduced canola establishment and increased pest damage. Using an Arricks wheel improved establishment in all treatments, and possibly more so in retained stubble than burned or grazed stubble. The demonstrations illustrated that different baiting methods and spray setups can make a difference to crop management and should be investigated further. This trial has shown that retained stubble systems in the high rainfall zone may be more profitable in the near future with further innovations by growers and researchers.


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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