By Paul Breust and Megan Beveridge, SFS
- No significant differences in phyto-toxicity and weed counts from stubble treatment or seeder used.
- Disc seeder establishment was significantly better and produced higher NDVI than tyne seeder establishment.
- No significant difference in establishment between burn, incorporate and retained treatments.
- Burn treated plots had significantly higher NDVI (read dry matter) than incorporated and retained.
- Retained stubble treatments were lowest for NDVI, even with similar establishment numbers, indicating lower crop vigour.
- Yield and grain weights for the disc seeder treatment were significantly lower than the tyne seeder at this sight despite better establishment and dry matter production early in the growing season. We are unsure of the reason why.
One of the major concerns with stubble retention systems is the impact on herbicide efficacy. Standing or prostrate stubble intercepts herbicide preventing it from being placed on the soil surface that it is targeted for.
In this study herbicide efficacy was tested in three stubble management practices:
- Retained and direct drilled
- Stubble incorporated with topdown
- Stubble burnt.
2014 was a Decile 1 year. Average annual rainfall in Westmere is 530mm but the trial site received only 370mm. Growing season rainfall (GSR) was a Decile 2, with Westmere receiving only 300mm from April to November compared to a long term average GSR of 400mm. Below average rainfall was recorded in every month except April and June.
Table 1: Agronomy for 14 GRDC STUB WHT MR in 2014. Tyne seeder on 20cm spaces, Disc on 18.5cm
|Sowing rate kg/ha||70kg/ha|
|Fertiliser||5/6/14||MAP 100kg/ha + 4ml Impact|
|Herbicide||3/6/14||Gramoxone 2l/ha PE|
|Herbicide||5-6-14||Sakura 118g/ha PE|
|Herbicide||5/6/14||Avadex 1.6l/ha PE|
|Herbicide||5/9/14||Axial 0.6l/ha Post E|
The tyne seeder used was Southern seeder with knife points on 20cm spacing.
The disc seeder used was Vaderstaad Rapid on 17.5cm spacing. The disc seeder engaged cultivation disc’s in front of seeding disc’s which gave a high level of incorporation for the stubble retained plots.
Stubble from wheat crop in 2013 was on 30cm spacing and was measured at 3.8t/ha dry matter.
Table 2: Establishment, NDVI, yield & grain weight results for 14 GRDC STUB WHT MR in 2014. Data followed by the same letter are not significant.
|Seeder||Est.||Sig. 0.05||NDVI||Sig. 0.05||Yield||Sig. 0.05||Weight||Sig. 0.05|
Table 3: Establishment, NDVI & yield results for stubble treatments in 14 GRDC STUB WHT MR. Data followed by the same letter are not significant.
|Stubble TRT||Est.||Sig. 0.05||NDVI||Sig. 0.05||Yield||Sig. 0.05|
The level of stubble, 3.8t/ha, is considered lower than regional levels in normal seasons and this would have reduced impact on herbicide efficacy.
The aggressive incorporation provided by the Vaderstaad Rapid disc setup would have provided a higher degree of incorporation than normally experienced with a single disc opener. This may have increased phyto-toxicity impacts on the crop in all disc treatments but conversely increased herbicide efficacy and weed control. Evaluation of phyto-toxicity and weed control found no significant differences between seeders or stubble treatments.
There were however positive significant differences in establishment and NDVI for the disc treatments. NDVI is a good indicator of dry matter production when measured before canopy closure. The differences did not contribute to higher yields for the disc treatments, in fact it had the opposite effect and the yields for the disc treatment were significantly lower than the tyne. This may have been a result of haying off at grain fill as a result of higher plant numbers using greater amounts of moisture during the season combined with poor spring rainfall.
Over all weed control was considered good. For this trial area there were very few grass weeds present as the Sakura and Avadex did a good job. The trial received a post emergent application of Axial only because it was beside another trial area that had significant grass weed issues and it was more efficient to apply to both trials. Velocity was used to control minor infestations of broadleaves.
No solid conclusions could be drawn for herbicide efficacy impacts of stubble management or seeder type. However it is clear retained stubble had no significant impact on establishment compared to burning and incorporating.
Retaining stubble however did negatively impact on early dry matter production as evidenced by significantly lower NDVI scores at growth stage 21. Past research supports this data but as also evidenced here there is minor impact on grain yields in a stubble retained system.
Further experimental work with commercial seeders will be conducted in 2015 to provide further evidence to support or refute impacts of stubble retention.
SFS gratefully appreciate and acknowledge the contributions of Myles Read and family and Swayne & McCabe in the running of this trial.
The stubble project – maintaining profitable farming systems in Victoria and Tasmania with retained stubble (project number BWD00024) is funded by the GRDC.