How much fertilizer does canola need?

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.

2023 Guidelines update the actual averages but this demonstrates general need and uptake by growth stage.

*Uptake and removal numbers in this article are based on results from the 2023 nutrient uptake and removal guidelines for Western Canada. These replace the Canadian Fertilizer Institute’s 2001 guidelines. The final report includes Table 3 that compares new and old removal guidelines and Table 5 that compares new and old uptake guidelines. Micronutrient results are shown in Tables 4 and 6.

Nitrogen (N)

Overall need

  • Crop uptake: 2.38 pounds per bushel, on average, with a range of 1.12 to 3.64.
  • Crop removal: 1.68 pounds per bushel, on average, with a range of 1.36 to 2.00. The rest remains on the field in straw, roots and other biomass.
  • Averages for a 50 bu./ac. canola crop: Uptake of 119 lb./ac. and removal of 84 lb./ac.

Estimating fertilizer rates

Soil tests will indicate soil nitrogen (N) reserves, but availability can be difficult to predict. Often about half the soil test is immobilized and not available to this year’s crop.

Soil tests will also indicate organic matter. 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.

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.

Try the new removal calculator. Note, the calculator rates are based on the 75th percentile numbers, not the average removal rates.

Canola Encyclopedia chapter on nitrogen management

Phosphorus (P2O5)

Overall need

  • Crop uptake: 0.90 pounds per bushel, on average, with a range of 0.40 to 1.40.
  • Crop removal: 0.67 pounds per bushel, on average, with a range of 0.52 to 0.82. The rest remains on the field in straw, roots and other biomass.
  • Averages for a 50 bu./ac. canola crop: Uptake of 45 lb./ac. and removal of 34 lb./ac.

Estimating fertilizer rates

If soil tests show available phosphate 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.

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 Encyclopedia chapter on phosphorus management

Sulphur (S)

Overall need

  • Crop uptake: 0.86 pounds per bushel, on average, with a range of 0.29 to 1.43.
  • Crop removal: 0.19 pounds per bushel, on average, with a range of 0.13 to 0.25. The rest remains on the field in straw, roots and other biomass.
  • Averages for a 50 bu./ac. canola crop: Uptake of 43 lb./ac. and removal of 9.5 lb./ac

Estimating fertilizer rates

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 Encyclopedia chapter on sulphur management

Potassium (K2O)

Overall need

  • Crop uptake: 2.93 pounds per bushel, on average, with a range of 1.51 to 4.35.
  • Crop removal: 0.35 pounds per bushel, on average, with a range of 0.28 to 0.42. The rest remains on the field in straw, roots and other biomass.
  • Averages for a 50 bu./ac. canola crop: Uptake of 147 lb./ac. and removal of 18 lb./ac

Estimating fertilizer rates

Canola is an excellent scavenger of K in the soil. 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. If soil tests show less than 250 pounds per acre (125 ppm), canola may benefit from a K application.

K deficiency is more likely to show up in coarse textured (sandy loam) soils in higher precipitation regions.

Canola Encyclopedia chapter on potassium management

Micronutrients

Canola takes up more boron than other micronutrients, but amounts are still low. The 2023 uptake and removal guidelines say canola takes up 0.336 pounds of boron per 100 bushels of canola seed.

The new Prairie Nutrient Removal Calculator includes boron, copper and zinc.

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.

Canola Encyclopedia chapter on micronutrients management

Moisture

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.

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