Many growers strive to apply all their fertilizer during the seeding pass. This one-pass system is a good way to save fuel, minimize soil disturbance and maintain the integrity of the seed bed, but it does present challenges for seed and fertilizer separation. Putting all seed and fertilizer down a single-shoot opener presents a high risk of seedling injury and a greatly reduced canola stand.
Growers need to keep nitrogen out of the seed row, for the most part. When applying 100 pounds of actual nitrogen per acre, for example, most or all of it should go in a side band, paired row or mid-row band away from seed and young emerged seedlings. Canola at its earliest stages needs very little nitrogen. When it needs nitrogen in larger amounts, it has the roots in place to go get it. Too much nitrogen at early stages can burn seed and seedlings, causing them to lose vigour and perhaps die. Nitrogen toxicity can also hinder early roots from accessing phosphorus — a nutrient the crop needs for early growth.
So how much seed placed nitrogen is too much? As this table (see below) from a Saskatchewan Ministry of Agriculture factsheet shows, tolerances for nitrogen in the canola seed row range from zero to 40 pounds per acre, depending on row width, row spacing, and soil conditions. For example, using a one-inch knife on 9-inch spacing and seeding in medium textured soil, seed-placed urea should not exceed 10 pounds of actual nitrogen (22 pounds of urea) per acre. Urease inhibitors and coated time-release prills make it safer to apply higher rates in the seed row, but even then growers still have a large amount of N to apply in a side band, paired row or mid-row band.
Click here for Manitoba seed-placed nutrient recommendations, which tend to be more conservative due to more calcareous soils.