Canola has a high nitrogen demand yet more than half of the nitrogen taken up is later returned to the soil. Nitrogen is the source of much of the yield but in excess may also reduce the oil content. Optimizing nitrogen fertilization is crucial and the subject of much research.
Canola is considered a crop with high phosphorous demand. Throughout the world, phosphorous is often the primary limiting factor on yield. The European countries seem to have rediscovered the importance of this nutrient.
Canola has a high demand for potassium from the end of winter until flowering, up to 400 kg/ha. Potassium is the nutrient with the highest rate of uptake. Even if 90% of the potassium is returned at the end of the season, the soil must be capable of satisfying these considerable demands at the period of maximum growth.
An often neglected nutrient, magnesium is required in significant quantities by canola. Magnesium nutrition is often fulfilled by “default” through the use of a magnesium containing lime or sulphur fertilization.
Sulphur is an example of a “secondary” nutrient which plays a “primary” role in canola nutrition. Its role is fundamental in amino acid production which is the precursor to protein, making it inseparable from nitrogen. Sulphur is taken up right through the growing season with uptake at its peak in the spring coincident with nitrogen. Application timing should be the same as nitrogen. Excess applications can interact with soil molybdenum creating a deficiency.
Boron is canola’s “major” micronutrient. Boron deficiency most frequently occurs on calcareous soils and when rapid cell formation and division is happening. Deficiency may cause significant yield and quality loss. It is therefore recommended to monitor the crop for deficiency through soil or plant analysis.
Closely linked to the assimilation of nitrogen, molybdenum is a “significant” micronutrient in all brassicas and deficiency occurs especially in acid soils. Excess applications of sulphur can cause molybdenum deficiency.
Manganese, copper and zinc deficiencies are fairly rare in canola, and copper or zinc deficiencies require no particular attention. Manganese may occasionally be seen due to its significant requirement by the canola.