Profitable stubble retention systems for the HRZ

By Paul Breust, SFS

KEY MESSAGES

  • When establishing canola into retained cereal stubble, seed should be coated with Cosmos or IBS, otherwise PSPE insecticides should be used
  • Inter row sowing is critical for the successful establishment of canola in cereal stubble
  • Canola establishment was reduced in stubble retained situations compared to burning
  • Canola establishment was reduced where urea was planted with the seed for both disc and tine seeders
  • Disc establishment was seriously reduced as a result of 25cm row spaced disc sowing in 30cm spaced stubble rows
  • Tine seeder plots had quicker emergence than the disc in dry sowing conditions
  • Metarex 7.5kg/ha plus Mesurol 2.5kg/ha baits, post sowing, increased emergence and decreased plant damage

BACKGROUND

The high rainfall zone (HRZ) commonly produces high yielding crops due to favourable environmental conditions. High yields also mean high stubble loads. Using the standard harvest index of 40% grain and 60% straw, a crop yielding 8 t/ha is likely to produce approximately 12 t/ha straw. In 2015, wheat yields averaged 3.4 t/ha across the trial. Stubble dry matter was measured at 5.75t/ ha for the disc and 5.00 t/ha for the tine prior to sowing in 2016. Using the average grain and stubble yields for the trial, end of season dry matter was 39% grain and 61% stubble, supporting the above rule of thumb.

High stubble loads can cause several problems for growers in the following season:

  • Seeder blockages which impact on plant establishment
  • Provides an ideal habitat for pests to survive
  • Interception of herbicide sprays especially pre-emergents
  • Increased frost risk (Paterson 2014)
  • Carry over of diseases such as Yellow Leaf Spot (YLS), Take-all and Crown-rot
  • Increased potential for nitrogen tie up.

Further to these, the common practice of reducing stubble loads through burning is becoming less popular with the wider public due to concerns with fire danger, health and safety, air quality and greenhouse gas emissions. This has prompted our investigation into other avenues for utilising stubble as an opportunity rather than burden.

The SFS section of the GRDC stubble project (BWD00024) aims to test and develop farming systems where retained stubble is managed in the HRZ without a reduction in profitability for the grower. To do this reliably, commercial harvesting and seeding equipment was used. Growers and advisors are leading the development of machinery and management practices and are contributing invaluable knowledge and experience to the stubble project. The stubble project draws on this knowledge along with research from other regions to develop a system that will be as profitable as traditional burning, baling and incorporation techniques the HRZ usually employs.

Retaining stubble has many positive impacts for crop production systems across all rainfall zones. Retained stubble provides excellent ground cover (>2.5 t/ha) thus reducing wind and water erosion, increases rainfall infiltration, reduces moisture evaporation (>4.5 t/ha), eliminates the need to burn, bale or incorporate and recycles nutrients back into the soil. Successful stubble retention requires a complex approach that considers every aspect of the system and their resulting impacts.

Harvesting is a major consideration for successful HRZ retained stubble systems. Several key points were highlighted through the project work in 2015 and in previous studies.

  • Harvest height should match your seeders capabilities to get through the crop; eg. disc 30 cm, tine 15 cm
  • There is a 10% loss of harvest speed for every 10 cm you lower the comb height
  • Trash that covers soil should be minimized to reduce blockages and improve pre-emergent herbicide efficacy
  • Chopper and spreader setup is critical to minimize blockages
  • Trash should be spread evenly across the header width
  • Traffic and livestock on stubble should be reduced to leave as much standing upright as possible

Table 1. Harvest efficiency data SFS disc versus tine trial 2015

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Table 2. Cost per hectare of sowing and harvest efficiency SFS disc versus tine trial 2015

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*Contract sowing @ $45/ha. 12 m disc takes 35 hr less time over 1000 ha at 12 km/hr versus 12 m tine at 8 km/hr

§1.98 extra minutes per ha valued at $6.66/min ($400/hr contract rate)

#2.11 L/ha less diesel valued at $1.20/L. Financial estimates of cost not yet available.

METHOD

The SFS ”Maintaining Profitable Farming Systems in Retained Stubble” project initiated one on farm trial and one demonstration in 2016, as detailed below.

1. Stubble management impacts on canola performance for John Deere 1890 disc seeder and Equaliser tine seeder

Aim

Determine the performance of canola established with disc and tine seeders into 5.38 t/ha wheat stubble in 2016.

Stubble treatments

JD disc – 30 cm high trash spread evenly across the swathe

Equaliser tine – 15 cm high trash spread evenly across the swath

Nitrogen – Split plot for plus or minus 60 kg/ha urea with the seed at sowing

Assessments

Pre-sowing moisture measurement, seeder trash handling, crop establishment, crop growth rates (measured by normalised difference vegetative index – NDVI), weed establishment, pest counts, DM at flowering, yield and harvest efficiency.

2. Stubble management impacts on canola performance with JD 1890 disc seeder (demonstration)

Aim

Determine the performance of canola established with a JD 1890 disc into 5.00 t/ha retained wheat stubble in 2016.

Stubble treatments

a. 30cm high trash spread evenly across the swathe

b. 15cm high trash spread evenly across swathe

c. 60cm high stubble after stripper front harvest

Assessments

Seeder trash handling, crop establishment, crop growth rates (NDVI and dry matter biomass {DM}), pest counts, DM at flowering and yield.

RESULTS AND DISCUSSION

1. Stubble management impacts on crop performance for JD 1890 disc and Equaliser tine seeders.

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ESTABLISHMENT

Seed row moisture was measured on the day of sowing and no significant differences were found. We measured it again 13 days after sowing. It was visibly obvious that the Equaliser tine sown strips had emerged quicker than the disc sown strips. There was very little difference between the disc and tine for seed row moisture. The grower hypothesised that the deeper disturbance of the knife point had raised moist soil to the top of the furrow allowing the seed to imbibe moisture and germinate faster.

Stubble clearly limited seedling establishment (table 3). The stubble emergence was severely restricted in the disc treatments as a result of using a seeder with 25cm row spaces into stubble with 30 cm row spaces. This has affected the overall result. In previous experiments where inter row sowing was used emergence has not been significantly different. The addition of Metarex, 8 kg/ha, and Mesurol, 2.5 kg/ha, baits increased establishment through better control of earwigs and millipedes which were epidemic at the site. Fiprinil (Cosmos) was not used on the seed but is recommended for anyone considering sowing canola into retained cereal stubble. No slugs were found at the site during the year.

Table 3. Canola establishment under the different treatments; +Urea is 60 kg/ha urea in seed furrow.

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*Results should be interpreted with caution due to the high level of variability in data.

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Figure 3. Comparative plots at the disc versus tine trial site. Disc sown areas were slower to emerge across the trial.

There was significant variation in the emergence plant counts across the trials, making the data less reliable. Overall, there was higher canola establishment under burned stubble than retained stubble (figure 4). Baiting increased establishment through better control of earwigs and millipedes.

While other trials have shown urea planted with the seed to negatively impact emergence and seedling vigor, in this trial stubble had a much greater negative impact on establishment than fertiliser with the seed. This is most likely a result of poor soil to seed contact in the retained stubble plots. This may be improved by inter-row sowing into good moisture when planting crops in retained stubble. Selecting larger seeded crop species, (e.g. beans, oats, barley) for rotation into retained cereal stubbles will also alleviate this impact.

Dry matter (DM) production

Plots were monitored throughout the season using a handheld GreenSeeker to measure the ‘greenness’ of the plots, or NDVI. Stubble retained plots had lower NDVI scores compared to burned plots, reflecting the poor establishment at seeding (table 4). Urea at sowing had an impact in the disc sown plots where it significantly reduced NDVI scores early in the season. There is conjecture on its value in retained stubble situations as the stubble changes the readings and brings into question its validity. The lower NDVI scores are considered strongly correlated to poor establishment from the seeding process.

Table 4. NDVI scores taken on the 14th July 2016

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DM cuts were collected at anthesis (table 5). Again, retained stubble had significantly lower DM at anthesis than burning. It is likely that low plant establishment in the stubble reduced overall DM production. Retaining stubble has been shown to limit nitrogen availability early in crop growth. At this site there were no significant differences in DM between plus or minus urea treatments except for the tine – burnt treatment. The disc – burn – plus urea treatment was significantly higher for dry matter than all other treatments. This may be an anomaly due to sampling error. There was no significant difference between any of the burnt treatments excepting this anomaly. The stubble – disc – minus urea was significantly lower for DM than the stubble – tine – minus urea.

Table 5. DM at anthesis (September 9, 2016)

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Nitrogen management is an important consideration for establishing crops into retained stubble. Fertiliser seed burn, early growth rates, pest tolerance, yields and grain quality are all strongly influenced by early nutrition. This is especially true for canola.

Application in furrow of liquid fertilisers may be one way of resolving this issue. They may reduce fertiliser burn and provide sufficient up front nutrition for the crop until later in crop nutrition can be applied.

Pests

There was a strong focus on pests in this trial in 2016. Slug tiles were distributed throughout the site but no slugs were found in 2016, which was fortunate for growers in the area as well as for the trial. Tiles were monitored and slug and insect bait strips were applied post sowing before emergence. Metarex at 8 kg/ha and Mesurol at 2.5 kg/ha were spread in 3 by 10 m strips at 90 degrees to the sowing direction. Plant damage and pest counts were collected at intervals throughout the season.

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Figure 4. Average Millipede numbers from 28 April to 28 June 2016 for disc and tine seeders in retained stubble or burnt stubble, plus or minus baits.

Baiting significantly reduced seedling damage at this site from 56% to 40% of plants (table 6). This was visible by eye at this site, however the level of damage was above what was considered a critical threshold level and so the grower applied an insecticide treatment to limit further damage. Millipede numbers were extremely high, peaking at almost 250/m2 in early May in the burnt disc treatment (figure 4). Millipede numbers in the burnt plots were much higher than in the retained stubble treatments. This is thought to be an effect of the monitoring method. The 30cm2 tiles provided the only refuge available in the burnt plots and this may have attracted a larger number of insects than in the stubble retained treatments. A reliable monitoring methodology for earwigs and millipedes is yet to be devised. SARDI, CSIRO and University of Melbourne are currently testing other methodologies for accuracy.

Table 6. Percentage of plants exhibiting leaf damage from insects, plus or minus baiting.

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From the data we could not be sure if the damage was a result of millipedes or earwigs that were present in low numbers. High numbers of millipedes have been experienced previously without serious seedling damage being evident. While unaligned with integrated pest management practices, prophylactic mollusc and insect control measures may need to be used until further data can be collected on existing pest species threshold numbers for seedling damage.

It is clear that seedling damage from a wide range of invertebrate pests is a critical consideration in retained stubble systems. Many crop establishment failures can be attributed to pests and retaining stubble residues provides an excellent habitat for pest survival and multiplication. Without successful and cost effective control methods, retaining stubble in the HRZ may not be a viable option.

Weeds

Weed emergence and survival were monitored in all trials. The sporadic nature of low weed emergence at this site limited the statistical significance of the data collected. No conclusions could be drawn from this site in 2016.

Yield

Yields were collected by the grower from the yield monitoring equipment. It was prepared for analysis by Precision Agriculture (see table 7).

Table 7. Yield (mean of treatments) SFS disc versus tine trial 2016.

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Means followed by same letter do not significantly differ.

Profit

The trial comparing a JD disc and Equalizer tine seeders in stubble retention systems demonstrated Western Districts of Victoria. Invertebrate pests caused severe seedling loss in stubble retained plots and establishment in the disc in stubble treatments were compromised by a change in seeder row space in the disc seeder used in 2016. Stubble row spaces were 30cm in 2015 and the seeder was on 25cm in 2016. The low canola establishment of the disc in stubble treatment would have contributed to lower yields and was reflected in the dry matter levels at anthesis. Previous trials (2015 results book) using canola inter row sown into wheat stubble have been successful and this year’s trial is not seen as a true representation of this system. However the results for 2016 do accurately reflect the potential losses that could be incurred if a stubble retention system is not managed well.

Table 8. Change in costs from shifting from a disc system to tine from the SFS disc versus tine trial 2015.

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*Contract sowing @ $45/ha. 12 m disc takes 35 hr less time over 1000 ha at 12 km/hr versus 12 m tine at 8 km/hr

†Canola valued at $520/t. Value of difference between disc and tine stubble treatments yields §1.98 extra minutes per ha valued at $6.66/min ($400/hr contract rate)

**2.11 L/ha less diesel valued at $1.20/L. Financial estimates of cost not yet available.

2. Stubble management impacts on canola performance with JD 1890 disc seeder demonstration

Stripper fronts are being used in LRZ regions to maximise the amount of stubble that is being retained. In low yielding years, stubble residues can fall below the recommended 2.5 t/ha if using a normal header front. The stripper plucks the head from the crop stem leaving as much stem standing in the paddock as possible. Stripper fronts also minimise the amount of stubble trash that ends up on the surface of the soil. This may have advantages in reducing seeder blockages, minimising pest habitat and increasing herbicide contact with the soil.

Stripper fronts have been shown to increase harvest efficiency and reduce fuel use due to processing much less of the straw or stem portion of the crop. In the HRZ where markets for stubble straw are common, using a stripper front may maximise the DM available for baling after harvest.

Southern Farming Systems, in collaboration with Neville, Grant and Troy Keating, implemented a demonstration to see how a stripper front would perform in the HRZ. This demonstration looked at sowing moisture, crop establishment, plant damage, NDVI, DM and yield. Two seeder widths of four stubble treatments were split for urea application at sowing: short (15cm), tall (30cm), stripper front (60cm) and burn.

The Keating’s use a JD 1890 disc seeder on 25cm row paces with no Arricks wheels (row cleaners). Hyola 650 Canola was sown on the 5th April 2016 into dry seedbed conditions. MAP at 100 kg/ha was sown with the canola seed.

Plots were split in two, with half receiving 100 kg/ha of urea at sowing. The canola was sown with every second disc unit on 60cm row spaces. Urea was placed in every other row to avoid fertiliser toxicity. Please note that no statistical conclusions can be drawn from the demonstration due to it not being replicated.

There was no discernible difference in seedbed moisture at sowing.

Sowing moisture, Establishment, Plant damage, NDVI, DM and Yield

Table 9. Monitoring data from throughout the season. Results based on 10 counts per plot

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The differences in stubble treatment for all measured parameters were inconclusive with wide variation in the same treatments and so it is hard to quantify any sound conclusions from the demonstration. Plant numbers were lower than desired and bait applications did not reduce plant damage scores at this site. NDVI readings varied but it appears that the burn treatment was marginally higher. This may be a result of the retained stubble impacting on the NDVI readings. DM was also inconclusive. In comparison to the burnt area surrounding the demonstration the retained stubble crop was less vigorous.

CONCLUSION

The results from work done in 2016 must be reviewed carefully and should be considered as one year’s data from one set of seasonal conditions. 2016 was an excellent year with grain yields being well above average for most crop species. There was widespread waterlogging damage in isolated areas of most paddocks which impacted on susceptible species such as canola. The dry start to 2016, with the seasonal break only coming on the 10th May, is thought to have increased seedling damage, especially in canola. It is hypothesised within the industry that insects eat seedlings to rehydrate in dry conditions, and once the season breaks they return to grazing decomposing plant material. There is no data to support this claim, only observations from within the industry.

The lack of slug pressure at all sites in 2016, while pleasing, should be considered a one-off opportunity. Data collected by Michael Nash has shown similar levels off slug activity post-harvest as was experienced in 2013/14. Moist spring conditions and large stubble residues are thought to contribute positively to increased breeding activity and survival rates of many pest species.

From the SFS project work, establishing canola in retained cereal stubbles in the HRZ is a difficult proposition. Conditions such as those experienced in 2016 can be regular events and adopters will need to pay attention to detail. Going forward, the 2017 sowing period may pose many of the challenges encountered in 2016 along with an increase in slug and snail pressure. Some growers have developed retained stubble systems that manage the many risks successfully. These growers are leading the development of individually tailored systems based on their experience, equipment and resources.

ACKNOWLEDGEMENTS

This project is funded by the GRDC (BWD00024)GRDCLogoStacked_TM_CMYK and carried out in collaboration with SFS, BCG, ICC and VNTFA.

Thanks to growers Myles Read, Charles Geddes, Neville, Grant and Troy Keating and Scott Blurton.

Also Jim Caldwell (SFS), Andy Medlyn (Harbergers Ag) Michael Nash (SARDI), Andrew Whitlock and Brendan Torpy (Precision Agriculture).

A printer-friendly version of this research report is available here.

REFERENCES

Baxter, N (2014) Close eye on research lifts WUE and saves sheep.

Condon, K (2014) Disc seeding, Experience a few years down the track.

Paterson, J (2014) Stubble lifts frost severity.

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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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