- CPM (Crop Production Magazine)
A “little and often” approach to spring fertiliser applications and tailored use of growth regulators are two important ways growers can help oilseed rape crops fulfil their promising yield potential this season, say Farmacy agronomists.
Low disease pressure and good weed control have resulted in many crops that are well forward, with strong root and canopy growth. Jason Noy, who looks after crops in Cambs, Herts, Wilts and Glos, says the first nitrogen has been applied to some early-sown crops that were beginning to look “hungry”, in order to ensure early development is not constrained.
“This is particularly true in the East where we’ve tended to drill OSR very early in the first or second week of Aug due to flea beetle pressure. Many crops had used up the standard dose applied at drilling, so received 45kgN/ha in early Feb.
“Even further west where OSR hasn’t been drilled so early, crops will benefit from nitrogen if it hasn’t already been applied. We don’t want to generate massive crop canopies, but equally we have to ensure the crop isn’t starved of nutrients.”
The aim with spring fertiliser applications is to achieve a green area index of 3.5 by flowering, and the focus for remaining nitrogen is usually around the stem extension timing. But Jason feels there are clear benefits from holding some back to apply later in the season to ensure the crop is well nourished during the important seed filling stage.
Norfolk-based agronomist Peter Riley agrees, and favours a four-way split, if farm logistics, equipment and product choice allow. The early dose would be followed by another at stem extension (usually mid-March), a third at green-bud stage in early April and a final dose of foliar urea at mid- to late-flowering. “A lot of research shows there are benefits from this kind of approach,” he points out.
“OSR also requires a lot of sulphur, especially when the crop is taking up nitrogen, so I often recommend applying both at the first three fertiliser timings. Sulphur can be very mobile in the soil though so it’s sensible to apply it as close as possible to when it is needed and will be quickly taken up by the crop.”
Additional micronutrients should also be applied as required, with boron in particular often needed – deficiency can impair stem elongation and flowering, he notes.
Jason believes a well-timed growth regulator can benefit large, forward crops and help create a canopy structure that maximises light interception throughout the growing season. Mepiquat + metconazole is his favoured choice at stem extension for growth regulation and height reduction. But he also suggests trinexapac-ethyl can be a useful alternative for canopy manipulation and creating a more even flowering period.
This works by reducing the plant’s apical dominance and encouraging side branches to flower at the same time as the main stem, he explains. “If flowering is less drawn out, it increases the window for light to penetrate the canopy after flowering which helps the plant to build yield potential through photosynthesis.”
Peter advises growers not to get caught out by applying growth regulators too late when crops are growing quickly in the spring. “We sometimes find growth regulators are being applied too late, which reduces their effectiveness. Ideally, they should go on at early stem extension, but sometimes they’re not actually going on until green bud stage which is too late.”
Spring disease control should now focus on sclerotinia sprays at flowering, he adds. He favours a two-spray approach including azoxystrobin and boscalid, while prothioconazole-based products are also worth considering, especially if there’s any light leaf spot or phoma to mop up.