Rainfall has renewed optimism in many key canola growing regions. Growers still have time to top up nitrogen and sulphur to take advantage of higher yield potential. Nitrogen should be applied before the 5-leaf stage to provide a strong economic benefit. Sulphur can be applied up to bolting. Click here for top up tips and photos of sulphur deficiency.
Apply whatever rate you feel is appropriate based on how much was applied earlier and the new yield potential of the crop. While there may be some leaf burn from high rates of nitrogen, the crop can usually grow through this damage without significant losses.
Efficacy can be very good for in crop applications. The key is to get a rain AFTER application to limit losses and move nutrient into the root zone. Uptake through leaves is minimal.
Rain that creates soil saturation can actually increase nitrogen losses due to denitrification, especially in fields with high residue. Crop residue, which provides a carbon-rich, nitrogen-poor food source for soil bacteria, will tie up (immobilize) fertilizer nitrogen stranded on the soil surface or in the shallow top layer. Whether using urea (dry) or UAN (liquid), Agrotain can limit losses while waiting for rain.
To minimize the effects of leaf burn, consider this tip: Apply liquid products when leaves are wet so the product runs off, but apply granular products in dry conditions since prills are less likely to stick to plant leaves.
Factors to consider before a top up:
—Nitrogen topdressing can extend the vegetative period and delay crop maturity. Consider the calendar date and the fall frost risk when making a nitrogen top up decision.
—As canola plants grow their roots will start to access sulphur reserves that moisture carried lower into the soil profile. Growers who have been applying recommended rates of sulphur may find that topdressing produces a smaller economic return than it does for those who have cut sulphur rates.