13 August 1999

OSR seed rate key to top yielding open canopies

CHOOSE oilseed rape seed rates which will deliver the open canopies needed to secure top yields next year, urges a top crop scientist.

To achieve the best rape yields growers must pay closer attention to seed rates and establishment, says Nottingham University crop physiologist David Stokes.

Careful planning now can help achieve the open canopies that deliver the highest rape yields, thanks to better light penetration to pods at the bottom of the canopy, he says. Open canopies also mature more uniformly and are easier to combine, perhaps without the need for desiccation at harvest.

Trials suggest a target of 5000-6000 pods a sq m. "These are crops where you should just be able to see through to a small amount of leaf material at the base of the crop."

That generally means a sowing rate nearer 60 seeds a sq m than 120/sq m. "Between 30-50 established plants a sq m is the ball-park figure to aim for in the spring," confirms Dr Stokes. "Then it is a case of ensuring nitrogen is available to prolong pod-fill in the open canopy."

Thick rape crops are likely to produce too many pods a sq m, leading to thin, lodging-prone stems and shading of later formed pods on side branches.

Farmers often say their best crops come from where they made a mistake in calibrating the drill, or where pigeon damage was significant, he notes. "These are crops that probably were not pampered – simply given the minimum attention – and the reason they did well is probably that they had just the right canopy to ensure strong pod formation and seed survival and growth."

But accurately predicting establishment success is not easy, Dr Stokes admits. "The problem is that there are so many variables to consider and, not surprisingly, growers are reluctant to reduce seed rates unless they can be sure they will get a good stand from a good seed-bed."

Take time to examine soil conditions before adjusting seed rates for each individual field this autumn, Dr Stokes advises.

Hybrids can be more vigorous in early seedling growth, giving growers greater confidence to use the reduced seed rates, he notes. "The more vigorous hybrids could help growers drill to a stand.

"And by planting at half the spacing traditionally employed for in-bred varieties, growers can benefit from hybrid vigour to ensure they have the right population to provide a productive summer canopy." &#42