Emergence a testing time for HRZ canola

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When growing canola in a stubble-retained system in the HRZ, separating seed from stubble, achieving good soil-to-seed contact and managing pests are key to success.

 

Key points

  • Avoid sowing canola in direct contact with heavy stubble residues. Instead use inter-row sowing or remove excess stubble.
  • Vigilant monitoring of pests, especially at the establishment stage, is required as stubble provides the perfect environment for insects, snails, slugs and mice.

Cereal stubble can lead to poor emergence and growth of canola.

Photo: Trent Potter

Canola provides a highly profitable and important weed and disease break for growers in the high-rainfall zone (HRZ). Yet the vulnerable canola seedlings struggle to establish in heavy cereal stubbles, proving a real challenge for growers hoping to reap the benefits of retained-stubble systems. Faced with heavy cereal stubbles growers often turn to burning to remove both stubble and pests, but would prefer to avoid this practice if they could find another way to improve canola emergence. As part of the GRDC’s Stubble Initiative, Southern Farming Systems, the Mid North High Rainfall Zone Group and the Yorke Peninsula Alkaline Soils Group have been looking at options with growers.

Poor competitor

Always a poor competitor at the establishment stage, canola was thought to suffer from allelochemicals released by cereal stubble or from nitrogen tie-up, but studies by CSIRO have dismissed these theories. In fact, it is simply the herculean struggle of a tiny seedling growing up through the stubble, with the exposed growing point very easily damaged at the cotyledon stage. As the hypocotyl has to grow further than in bare soil the plant’s energy reserves are exhausted and the elongated hypocotyl seedling is more vulnerable to soil-borne diseases. Canola establishes better when the seed is kept separate from retained stubble and good seed-to-soil contact is achieved.

Inter-row sowing is one of the most successful ways of separating seed from stubble and increasing seed-to-soil contact, but requires wider row spacing and erect stubble with minimal inter-row residue. Unlike cereals, canola plants compensate well for wider row spacing, maintaining both yield and competitiveness against weeds. Minimising seeder blockages and hairpinning at sowing is important and can be improved by increasing the row spacing. Some growers are fitting row cleaning attachments to seeders to sweep aside the loose stubble in the inter-row area.

Another option is to grow highly vigorous pulse crops, such as faba beans or lupins, following cereals that promote stubble breakdown to reduce stubble loads before planting canola, with the added bonus of increasing the supply of nitrogen for the canola crop.

Table 1. Overcoming the challenges of establishing canola in retained cereal stubble in the high-rainfall zone.

ProblemCause Potential remedy
Seeder blockages High stubble residue Inter-row sowing, even trash spread, wide rows
Poor soil-seed contact Hairpinning straw and trash in soil Inter-row sowing, erect stubble, rotations, burning
Seedling damage Insects, slugs and snails eat seedlings Burning, rolling, seed dressings, baiting, insecticides
Lower early vigour Contact with stubble reduces vigour Inter-row sowing, erect stubble, hybrid or >2mm retained seed
Shading in early growth stages Short stubble, wider row spaces, hybrid or >2mm retained seed
Nitrogen tie-up Apply nitrogen before or at sowing, early post-emergent application

SOURCE: Southern Farming Systems

Monitor pests

Snails, slugs, insect pests and mice are also serious threats to canola establishment, with stubble providing the perfect habitat for them to survive and thrive. Stubble cover and the sporadic nature of pest infestations also make it difficult for researchers to effectively monitor pests and develop strategies. Most growers rely on baiting, insecticide seed treatments or other ‘insurance’ applications to keep on top of pests.

Achieving good establishment of canola requires attention to detail including the selection of high-quality hybrid seed, or grading retained seed (greater than 2mm in size) to select the larger fraction. In heavy cereal stubble loads (more than six tonnes per hectare) removing all or part of the stubble as late as possible will provide most of the benefits of stubble retention and eliminate many of the problems.

Strategic stubble burning prior to sowing may also assist with snail and slug control and can reduce blackleg risk by removing previous canola stubble from the inter-row. Other options available for successful canola establishment in heavy stubbles include baling, heavy grazing or other stubble removal activities.

GRDC Research Codes BWD00024, YCR00003

More information:

Jon Midwood, Southern Farming Systems
0400 666 434
jmidwood@sfs.org.au

Trent Potter, Yeruga Crop Research
0427 608 306
trent@yeruga.com.au

The Stubble Project