There has been limited research on winter canola fertility in Ontario. Recommendations are adopted from other regions and based on known fertilizer requirements in spring canola, which is the same species as winter canola.
The high rates of nitrogen and sulphur required, and the seeding methods used make it inconvenient and risky to apply all fertilizer requirements with the seed. Many Ontario producers apply low rates of phosphorous with the seed. Nitrogen and sulphur requirements are split across an application at or before seeding and spring applications.
Maximum Safe Rates of Seed-Placed Nutrients
Up to 28 kg/ha (25 lb/acre) of phosphate (P205) may be seed-placed as ammoniated phosphate, or as superphosphate or MAP. Ensure the rate of nitrogen placed with the seed does not exceed 11 kg/ha (10 lb/acre).
The rate of nitrogen, potash (K2O) and sulphur placed with the seed must not exceed 11 to 33 kg/ha (10 to 30 lb/acre) depending on soil type. The lower rate is applicable on sandy loam soils.
Ammonium sulphate has a high salt index and rates above 22 kg S/ha (20 lb S/acre) can reduce emergence, especially in dry conditions.
Nitrogen
Canola has a great demand for nitrogen (N). Previous recommendations for Ontario producers based on a price ratio of nitrogen cost to grain price are outdated, and limited research has been conducted in recent years. Based on uptake and removal guidelines for spring canola in Western Canada that were updated in 2023, canola requires an average of 47.6 kg N/ MT (2.38 lb N/bu) of canola. This means a crop yielding 3929 kg/ha (70 bu/ac or 1.59 tonne/ac) requires 187 kg/ha (167 lb N/ac).
Nitrogen application ahead of seeding is recommended to ensure plants grow quickly and are not stunted or nitrogen deficient, to support winter survival. Kansas State University recommend a minimum of 34 kg/ha (30 lb N/ac) in the fall or about one third of the total nitrogen requirement, and also state that too little or too much fall-applied N can negatively affect winter survival. On-farm experience in Ontario has shown that about 45 kg/ha (40 lb N/ac) ahead of seeding supports vigorous early season growth and may improve winter survival compared to no nitrogen. Where manure has been applied there may not be a need for synthetic fertilizer.
Nitrogen should not be placed with the seed. Seedlings are sensitive to ammonia toxicity and the salt effect of fertilizers that causes desiccation of seedlings. Nitrogen fertilizer is typically broadcast ahead of seeding, but where equipment allows it can be banded 5–7.5 cm (2–3 in.) to the side of the seed row.
Local research is needed to improve nitrogen rate recommendations in Ontario; however, past recommendations have been to apply 45 kg/ha (40 lb N/ac) at seeding and an additional 168 kg/ha (150 lb N/ac) when growth resumes in spring, prior to bolting. This has worked well for producers in recent years. In a few cases where producers have applied higher rates in spring, they have not recorded increased yields. The maximum rates of nitrogen uptake occur during bolting through to mid-bloom. Monitor the crop for new growth at the center of the rosette in spring and apply nitrogen as soon as weather allows prior to reproductive growth. Canola produces flower buds down in the whorl of the plant prior to bolting. If fertilizer application is not possible prior to bolting, it is still beneficial to apply nitrogen up to the time the first few flowers open on each plant. If plants look deficient during early bloom some yield potential may be lost, and nitrogen rates can be adjusted down by about 25%.
In some winter canola-producing regions of the world it is common to split the spring fertilizer across two applications; the first prior to bolting and the second during early bloom. This may not be as practical in Ontario where we have longer, harsher winters and more precipitation than in other regions. In Ontario, winter canola advances very quickly from green-up to first flower, and there may be as few as two weeks between pre-bolt and first flower stages. While applications during early bloom may benefit the canola crop, the most economical application timing for spring nitrogen is prior to bolting.
If canola plants are still in vegetative growth stages and are relatively flat with growing points low to the ground, wide tires can be used for spring fertilizer applications. If growing points are raised, which may occur with excessive fall growth and very large plants, or if the canola has begun to bolt, the plants can be significantly damaged by sprayer or spreader tires so a narrow tire that runs over fewer plants is recommended.
There is some risk of injury with top dressing high rates of nitrogen, but in-crop applications can be safely applied by broadcasting dry (urea) products or dribble banding liquid (UAN) products. Granular products should be applied when leaves are dry, while liquid products should be applied when leaves are moist, to reduce the potential of fertilizer sitting on leaves. Liquid products may cause some burn or stress so herbicides should not be applied for a few days after fertilizer application.
Nitrogen deficiency appears as premature yellowing of the older, lower leaves. Deficient plants may appear spindly and thin and have an overall pale or yellow colour. In some cases, particularly with nitrogen deficiency observed in the fall during vegetative growth stages, leaves may have a range of colours including yellow, orange and purple on lower leaves (Figure 1). Healthy leaves are a dark blue-green colour.
Figure 1. Nitrogen deficiency visible on lower leaves in late fall in a field that has not had nitrogen applied.
Sulphur
Canola has a much higher requirement for sulphur (S) than most other field crops grown in Ontario. Sulphur levels can be variable across a field and sulphur is mobile in the soil. It is critical to apply sulphate to avoid deficiencies. A deficiency can occur at any crop stage and can reduce yields. The current guideline is to apply 28 to 40 kg/ha (25 to 35 lb/acre) of sulphate. According to the recently updated guidelines on nutrient uptake and removal in Western Canadian spring canola, canola requires 17.1 kg S/MT (0.86 lb S/bu) so an average Ontario crop yielding 3923 kg/ha (70 bu/ac or 1.59 tonne/ac) requires 67 kg S/ha (60 lb S/ac).
Sulphur deficiencies can be corrected with top dressing at any time prior to pod development, and deficiency in the seedling stage is typically only observed if severe. For these reasons, it may be acceptable to apply the full rate of sulphur during the early spring prior to bolting. However, studies conducted in spring canola show that sulphur uptake is rapid in the seedling stages and peaks during the first 6 weeks of growth. In addition, wet soil conditions in spring sometimes prevent fertilizer application prior to bolting. It is therefore recommended to apply some sulphur at seeding and the remainder in spring prior to bolting; an application of 17 kg S/ha (15 lb S/ac), or up to half of the planned sulphur rate, is adequate at seeding.
While some sulphur will be supplied by the soil, annual application of sulphate is recommended. Complete conversion of elemental sulphur to the usable sulphate form can take 2 to 3 years so application of elemental sulphur is unlikely to be available in time to meet crop needs.
Sulphur is linked to soil organic matter and is mobile, like nitrogen. Sulphur deficiency is more likely to occur on sandy or open bottom soils with low organic matter. While sulphur is ideally applied prior to bolting, applications up to the early flowering stage may provide a yield benefit where deficiencies exist. Effective absorption of sulphur occurs when foliar applications are made during the evening or early morning when temperatures are moderate, and under high humidity conditions.
Sulphur deficiency may appear as yellowing and upward cupping of new leaves. These symptoms are often accompanied by purple colouring at leaf edges or on the back of the leaf due to anthocyanin pigments caused by sugar buildup resulting from the deficiency (Figure 2). Sulphur deficiency in the seedling stage is typically only observed if the deficiency is severe. During flowering stages, deficient plants have small, pale flowers (Figure 3). If deficiency occurs during later growth stages, plants may display symptomatic flowers, but leaves may not show symptoms.
Figure 2. Sulphur deficiency (left) results in mottling of the leaf surface, purple underside of leaves and small, pale-yellow flowers.
Figure 3. Sulphur deficient plants observed during bloom stages may not express symptoms on leaves but may have smaller, pale flowers (left).
Phosphate and Potash
Phosphate and potash recommendations for canola are based on OMAFA-accredited soil tests, as provided in Tables 1 and 2[MM(1] . The phosphorus requirements of canola are greater than for cereals, due to the higher protein content of the seed. The nutrient uptake and removal guidelines for Western Canada indicate an average of 18 kg P/MT (0.90 lb P/bu) is taken up by the crop and 13.4 kg P/MT (0.67 lb/bu) is removed in the grain. Although canola is responsive to starter phosphorous it is also sensitive to salt injury, refer to Table 9–22, Chapter 9, Maximum safe rates of nutrients in fertilizer.
Canola requires 50 kg K/MT (2.5 lb K/bu) per bushel. Most potassium remains in the plant biomass and is returned to the soil. Yield response to potassium is expected on soils with less than 100 ppm (Table 2).
Table 1. Phosphate guidelines for canola
| Sodium Bicarbonate Phosphorus Soil Test | Phosphate Required |
| 0–3 ppm | 70 kg/ha (HR) |
| 4–5 ppm | 60 kg/ha (HR) |
| 6–7 ppm | 50 kg/ha (HR) |
| 8–9 ppm | 30 kg/ha (HR) |
| 10–12 ppm | 20 kg/ha (MR) |
| 13–15 ppm | 20 kg/ha (MR) |
| 16–30 ppm | 0 (LR) |
| 31–60 ppm | 0 (RR) |
| 61 ppm + | 0 (NR)1 |
| 100 kg/ha = 90 lb/acre | |
| Legend: HR = high response MR = medium response LR = low response RR = rare response NR = no response | |
| 1 When the response rating for a nutrient is “NR,” application of phosphorus in fertilizer or manure may reduce crop yield or quality. For example, phosphorus applications may induce zinc deficiency on soils low in zinc and may increase the risk of water pollution. Based on OMAFRA-accredited soil tests. Profitable response to applied nutrients occurs when the increase in crop value, from increased yield or quality, is greater than the cost of the applied nutrient. Where manure is applied, reduce the fertilizer application according to the amount and quality of manure (Chapter 9, Manure section).[MM(2] | |
Table 2. Potash guidelines for canola
| Ammonium Acetate Potassium Soil Test | Potash Required |
| 0–15 ppm | 70 kg/ha (HR) |
| 16–30 ppm | 50 kg/ha (HR) |
| 31–45 ppm | 40 kg/ha (HR) |
| 46–60 ppm | 30 kg/ha (HR) |
| 61–80 ppm | 20 kg/ha (MR) |
| 81–100 ppm | 20 kg/ha (MR) |
| 101–120 ppm | 0 (LR) |
| 121–250 ppm | 0 (RR) |
| 251 ppm + | 0 (NR)1 |
| 100 kg/ha = 90 lb/acre | |
| Legend: HR = high response MR = medium response LR = low response RR = rare response NR = no response | |
| 1 When the response rating for a nutrient is “NR,” application of potash in fertilizer or manure may reduce crop yield or quality. For example, potash applications may induce magnesium deficiency on soils low in magnesium. Based on OMAFRA-accredited soil tests. Profitable response to applied nutrients occurs when the increase in crop value, from increased yield or quality, is greater than the cost of the applied nutrient. Where manure is applied, reduce the fertilizer application according to the amount and quality of manure (Chapter 9, Manure section). | |
Canola takes up phosphorus from the soil rapidly in the early growth stages and continues to remove phosphorus for up to about 8 weeks. Although canola requires a large amount of phosphorus, canola successfully scavenges phosphorous from the soil profile and maximum yields are attained at generally lower rates than that for most spring cereals. Canola is non-mycorrhizal and does not utilize fungal networks in soil to take up phosphorous. The roots of canola will proliferate extensively in banded fertilizer phosphorus.
When applying phosphorus, an adequate supply near the seed row is important for early access. When broadcast, 2–4 times more P is required to obtain the same yield response as banded P, and broadcast P is also at higher risk for runoff. Canadian research indicates that canola yields are optimized with an initial 17–22 kg/ha (15–20 lb/acre) of starter P205, even on soils with high fertility levels. Response to starter P is more likely on cold, low fertility soils, when planting early. Canola research has verified that MAP (11-52-0) is equally effective to other dry starters and liquid P fertilizer materials. The impact of starter fertilizer on early growth can be seen in Figure 3[MM(3] where on a medium fertility level soil, the crop on the left side of the photo had no starter fertilizer applied, while on the right side of the photo the crop received 55 kg/ha (50 lb/acre) of MAP as a starter fertilizer at planting.
Figure 3. The impact of early canola growth is evident for this medium fertility field, where the crop on the left side had no starter fertilizer applied while the crop on the right side the crop received 55 kg/ha (50 lbs/acre) of MAP at planting.
Boron
Boron deficiencies are rare in canola. Ontario field trials with foliar boron 0.34 kg/ha (0.3 lb/acre) applied at early flower did not show a consistent economic yield response. Although rarely seen, when it occurs it can reduce yields significantly.
Symptoms can include:
- Stunted appearance
- Brown areas in pith of the stem or cracked stems
- Brown to reddish coloured new leaves and yellow to brown spots in between leaf veins
- Cupping of leaves
- Prolonged flowering and poor pollination
Boron deficiency can be corrected with either foliar or soil applications of soluble boron fertilizers. Although there is little evidence of an economic response to boron applications, soil applied pre-plant applications and addition of boron to fungicide applications are common in Ontario.