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Canola is highly sensitive to seed-placed fertilizer in general, but especially nitrogen, potash and ammonium sulphate. The only beneficial fertilizer to safely place with canola seed is phosphate, and even then, there are limits. Safe rates are 20 lb./ac. (40 lb./ac. of MAP) in general, and 25 lb./ac. with wider openers.
Although canola stands can compensate to some degree for thinning due to seed-placed fertilizer, keeping safe rates of phosphate with the seed and placing the remaining fertilizer in a band away from the seed will help establish a uniform, earlier maturing crop,
U of M soil scientist Don Flaten says these three points represent the “bottom line” for seed-placed fertilizer in canola:
1. Apply plant available sources of nutrients. Elemental S, for example, may increase seed-placed safety, but it will not necessarily be available for uptake when the crop needs it.
2. Place a modest rate of P in the seedrow. At rates over 20 lb./ac., the salt component in MAP, for example, can start to set back seedling survival. Cereals can tolerate higher rates of seed-placed phosphate, so the cereal phase of a crop rotation provides a better opportunity to apply higher rates needed to rebuild soil P reserves when necessary.
3. Place N and S in a band away from the seed.
The seedbed utilization (SBU) dilemma: Narrow row width and higher opener spread will increase SBU and can make it possible to safely apply higher rates of seed-placed fertilizer. However, higher SBU also means the phosphate fertilizer young canola plants really need is spread out farther from the seed. The 20 lb./ac. phosphate rate may be inadequate with high SBU. Phosphate, at the safe rate your equipment allows, should be in a tight band with the seed.