Canola in Western Canada generally needs nitrogen, phosphorus and sulphur fertilizer each year, and a small percentage of fields will also benefit from a potassium application. Nutrients in soil and crop residue will provide some of that need. The rest will come from fertilizer. A fertilizer program based on yield goals, 4R practices and current soil nutrient levels will improve profitability.
The 2023 nutrient uptake and removal guidelines for Western Canada put average nitrogen uptake for canola at 2.38 pounds per bushel, with a wide range of 1.12 to 3.64. This is less than the Canadian Fertilizer Institute’s 2001 guidelines, which averaged 3.19 with a range of 2.85 to 3.51. See Table 5 here for a comparison of new and old guidelines.
Soil tests will indicate soil reserves, but available carryover nitrogen can be difficult to predict. Often about half the soil test N is immobilized and not available to this year’s crop.
Mineralization of soil organic matter (OM) will provide available nitrogen to the crop, but the amount varies widely based on soil type, soil OM levels and moisture. In general, OM can generate 6 to 30 pounds of available nitrogen per acre for each percentage point of OM. Rigas Karamanos uses 14 lb./ac. per OM%. Of that amount, only 80% is available to the crop that year. Using Karamanos’s number, soil with 4% OM will supply 45 lb./ac. of N through the growing season (4 x 14 x 0.80 = 45). He adds that mineralization can increase by up to 25% with more than average moisture and be 25% lower in drier conditions, which makes predicting mineralization rates a challenge.
Losses should also be considered. High straw loads and poor fertilizer placement (such as broadcasting) mean more N than normal may be immobilized or temporarily tied up early in the season when canola is needing nitrogen. North Dakota State University (NDSU) estimates about 30 lb./ac. of N is immobilized for every ton per acre of cereal straw.
Of the N canola takes up, around 70% is removed with the seed and 30% is returned to the field in the residue. Try the new removal calculator. Note, the calculator rates are based on the 75th percentile numbers, not the average removal rates.
According to the 2023 nutrient and removal guidelines, average phosphorus (P2O5) uptake for canola is 0.90 lb./bu. crop, with a range from 0.40 to 1.30.
Of the phosphate canola takes up, around 67% is removed with the seed and 33% is returned to the field in crop residue.
If soil tests show available P levels at less than 10 parts per million (20 lb./ac.), this is considered “low” and growers may want to use a rate higher than crop removal to build soil reserves. At a soil test of 10-20 ppm, rates that match removal are recommended.
Harvested canola removes an average of 0.67 lb./bu., so a 50 bu./ac. canola crop could remove 33.5 lb./ac. of phosphate, based on the new guidelines. When planning phosphate fertilizer applications, note that a safe seed-placed rate of 20 lb./ac. of phosphate will ensure that canola has access to phosphate fertilizer and the benefit of early pop up. This is especially important when seeding into cool soils with low P levels, into soils with pH outside the sweet spot of 6.5-7, and in short-season areas. The rest can go with the nitrogen blend placed outside the seed row, ideally in a band.
Canola takes up an average of 0.86 pounds of sulphur (S) per bushel of yield, making it a high S-using crop. This number, taken from the new guidelines, is quite a bit higher than the 2001 guidelines, which put the average at 0.54. See Table 5 here.
A 50 bu./ac. canola crop needs 43 lb./ac. of available S, although the range in the new guidelines is very wide.
Fertilizer rate recommendations are based on the total need (uptake) minus the soil reserves, however a fair estimation of soil reserves is not always possible with a soil test. That’s because S is often highly variable across a field – it might be 10 pounds per acre in one corner and 2,000 pounds in another. If soil is low in S, fertilize according to soil test recommendations. If soil is moderate or high in S, some S in the fertilizer blend – say 10-15 lb./ac. – may be required to offset the high amount of S-test variability in a field.
Canola plants need 2.93 pounds of potassium (K2O) for every bushel of seed yield, according to the new guidelines. Like sulphur, this is higher than the CFI factsheet, which averaged 2.31. A 50 bu./ac. crop can take up 147 lb./ac. of potassium, on average. Of the K canola takes up, over 80% is returned to the field in the residue.
Canola is an excellent scavenger of K in the soil and because the relatively “young” Prairie soils continue to produce plant-available K through break-down of clay minerals, canola crops have rarely shown a response to K fertilizer. But if soil tests show less than 250 pounds per acre (125 ppm), canola may benefit from a K application.
Long-time Alberta soil scientist and fertilizer expert Ross McKenzie estimates that 20-25% of fields on the Canadian Prairies could have soil K levels in the deficiency range for canola. He says soils most likely to show K deficiency are intensively cropped, coarse textured (sandy loam) and tend to be in the higher precipitation regions in the Black and Gray soil zones.
Canola takes up more boron than other micronutrients, but amounts are still low. Tissue analysis of canola at flowering show sufficiency at these levels: 29 parts per million (ppm) for boron, 19 ppm for iron, 14 for manganese, 14 for zinc, 2.6 for copper and 0.02 for molybdenum. The new Prairie Nutrient Removal Calculator includes boron, copper and zinc for 14 crops.
The Canola Council of Canada boron trials, done as part of the Ultimate Canola Challenge for 2013-15, found no consistent yield benefit from boron treatment, including in those plots with very high yield results. Read more.
Moisture is a major limiting factor for canola yield potential and must be included when setting fertilizer rates and budgets. Although dependent on evapo-transpiration potential, the general rule is that canola needs an inch of available moisture through the growing season for every four bushels per acre of yield potential. A 50-bushel crop will need roughly 12 inches of moisture.
- Final report for “Revising the crop nutrient uptake and removal guidelines for Western Canada” which has removal (Table 3) and uptake (Table 5) for 14 crops grown in Western Canada.
- Prairie nutrient removal calculator. Compare 14 crops.
- Canola Encyclopedia
- Canola Discovery Forum 4R panel – Q&A, and more
- Fertilizer Canada’s 4R principles
- PODCAST – fertilizer planning
- Canola Digest articles:
- Simple 4R tips to improve profitability
- Soil sampling as a step toward improved land use
- Use 4R to show the benefits of modern agriculture
- Why are low-yielding areas low yielding?
- Canola Research Hub: