II.3. BRASSICA CROPS (BRASSICA SPP.) – 181
The seeding rates recommended for precision drilled hybrid varieties with a high
branching density and a 1 000 seed weight of 4 g/1 000 is 1.2-1.6 kg per hectare and for
seed of 7 g/1 000, 2.1-2.8 kg per hectare. The seeding rates for drilled hybrids are lower
than for open pollinated varieties since the hybrid seed is likely to produce a more
vigorous plant that better withstands the winter. The optimum spring plant population is
reported to be 80-100 plants/m². Winter varieties are heavy users of nitrogen so
frequently some nitrogen is incorporated prior to planting, with the balance top-dressed in
the spring. Excessive nitrogen promotes vigorous fall growth but tends to make the crop
more susceptible to winter kill. Phosphorus and potassium are applied before planting at
the recommended levels. Sulfur is used in early spring in combination with
N-fertilization. Boron is often applied in late spring in combination with fungicides.
Nearly all seed is treated with a fungicide-insecticide combination (often with more than
two active ingredients) to control seedling pests.
Disease, insect and weed control in the emerged crop is achieved by spraying the
recommended products when needed. Flowering in northern Europe begins the last days
in April, and harvest starts with some swathing at the end of July with the vast majority of
the crop straight combined a week or so later. Harvest can continue through to the end of
August. In southern regions, harvest commences about one to four weeks earlier.
Australian crop cultivation and management
Oilseed rape production in Australia is relatively recent with the first commercial
production undertaken in 1969. In the early years, both B. rapa and B. napus spring
varieties from Canada were imported and grown in the winter season. Today production
is almost exclusively from Australian-bred B. napus varieties. Canola is grown in most
cropping areas of Southern Australia, including Western Australia (Figure 3.29). Most of
the B. napus crop is sown in late autumn or early winter (April to June) during the rainy
period. The seed is primarily sown with air seeders at seeding rates of 4-6 kg per hectare
with hybrid varieties being sown at about 3 kg per hectare. All seed is treated to control
blackleg disease (Leptosphaeria maculans [Desm.] Ces. et de Not.) and some seed is
treated for control of the red-legged earth mite (Halotydeus destructor Tucker).
Flowering occurs in August and September with harvest in late spring or early summer
(November and December). The growing season ranges from about 150-210 days,
depending on latitude, rainfall, temperature and sowing date. Growth and yield of the
crop is almost always limited by the amount of water available to the crop, particularly
during maturation.
Due to the age of Australian soils, macronutrients (particularly nitrogen, phosphorous
and sulphur) and micronutrients are deficient. Deficiencies in boron, manganese,
molybdenum and zinc have been reported for B. napus crops, as has toxicity on the more
acid soils due to high levels of aluminium and manganese. Most soils are strongly acidic
and liming is necessary to achieve high yields. Initially oilseed rape was sown into
well-worked soil, but with the availability of glyphosate as a pre-planting herbicide and
varieties resistant to triazine and imidazolinone herbicides, direct seeding has become
standard practice.
Oilseed rape is most frequently preceded by a pulse crop or pasture while fallow and
wheat are other alternatives. When the canola crop precedes wheat in the rotation,
substantial wheat yield benefits occur.