Rotation effects
Canola can reduce the incidence of some cereal root and crown diseases, such as crown rot and take-all.
Research has shown canola to be the most effective winter crop for reducing crown rot levels in subsequent wheat crops.
Canola can have both positive and negative effects on subsequent crops. Canola is non-mycorrizal, and so VAM levels can fall under canola.
This may disadvantage crops sown after canola, which are highly dependent on VAM.
Crops affected include all commonly grown summer crops (sorghum, cotton, maize, sunflower and the summer pulses) as well as faba bean and chickpea.
Wheat, barley and oats have a low dependence on VAM, and so can be readily grown in rotation with canola. As canola reduces VAM levels the same way as long fallows do, canola should be grown with short (about 6 months) fallows before and after it.
Research has shown that wheat yield increases in the order of 0.6–1.0 t/ha can be expected when following canola compared to wheat following wheat.
Zero tillage, which retains more stubble, is increasing the carryover of many of the main cereal diseases, such as crown rot, in northern NSW. Canola fits well into this system by allowing an additional season for cereal stubble breakdown to occur and therefore reducing the carryover of disease.
Tractor Sowing Canola
Maintaining a rotation of one canola crop every four years also minimises the potential for disease build-up in the canola. The use of triazine tolerant varieties has helped to control difficult weeds such as bindweed and fleabane.
Rutherglen bugs may be present in large numbers on canola stubble around harvest time. These can readily move into neighbouring summer crops or crops planted directly into the canola stubble causing serious damage.
Sowing
Early sowings maximise yield potential and oil content but sowing too early increases the risk of frost damage during the late flowering and pod-filling stages.
Sow mid season varieties from early May and early maturing varieties from mid May. Delay sowing further in paddocks known to have high frost risk.
Seek guidance from experienced agronomists in your district, but in general finish sowings by about June 1 around Moree and June 15 south of Gunnedah. Within these guidelines, consider sowing several varieties with different maturities and even several sowing times to spread the risks of unforeseen seasonal factors such as moisture stress or frost.
Canola usually flowers for 3–5 weeks, and frost damage is greatest if it occurs towards the end of flowering and through pod filling. Early maturing varieties sown at the beginning of May would be subject to frosts in the late flowering and pod-filling stages, whereas mid season varieties will flower and fill pods later, reducing the risk of frost damage.
The small seeds of canola need to be sown ideally no more than 5 cm deep in self-mulching clays (2–3 cm in red soils) into well prepared, moist seedbeds. Good seed-soil contact, to help ensure uniform establishment, is aided by the use of rollers, culti packers and press wheels. The crop is suited to conventional and no-till systems.
Heavy stubble loads may reduce emergence, and should not be left over the sowing row. Triazine tolerant varieties are less vigorous so planting methods are more critical for even establishment.
Aim to establish 30 to 50 plants per m2 in northern NSW, which can be achieved with 2–4 kg/ha of seed (provided it is good quality seed).
Variety Selection
The main features to consider when selecting a variety are: maturity, yield, oil content, herbicide tolerance and blackleg resistance. Early maturing varieties are generally more suited to drier western areas, and mid season types to favoured growing areas.
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