Set aside the pub talk and be honest: are you really achieving a consistent 5t/ha off your oilseed rape, or was it just a bumper patch in one field that flicked up on the combine yield monitor?
The truth is the five-tonne crop remains the Holy Grail for OSR growers. It’s a worthwhile target with rich rewards for those who can achieve it as an average. So what’s the secret?
We’ve asked some of the nation’s experts and narrowed it down to three essentials:
• Managing the root
• Managing the canopy
• Managing disease
But there are many more factors, such as crop development, seed vigour, cultivation technique and micronutrients that complete the story.
The route to a good root
More than any other crop, good establishment is vital and, as with all good agronomy, it starts with the soil. From a tiny seed, OSR develops a long, strong tap root. Conditions at establishment have a huge bearing on this process.
“Oilseed rape is very lazy at rooting,” says Masstock agronomist Philip Marr. “The slightest bit of compaction and it starts going sideways, leading to a poor root structure and a poor crop.” Compaction resistance must be removed to allow easy passage for the root through the soil profile.
Establishment technique and seed rate can vary, but good soil-to-seed contact is essential to get the process started.
For more on this: See all of the articles on High 5 OSR yields
“You can get a good crop from just 30 plants/sq m in the autumn so long as every seed is placed so that it can put its roots down deeply,” says Hampshire AICC agronomist Steve Cook.
The surest way to encourage this is to give the seed a kick-start – a dose of nitrogen in the seed-bed. Again technique can vary – it can be liquid or prilled, applied in bands, dressed on the seed, or released from the soil through cultivation.
Yorkshire agronomist Andrew Beeney says: “Good early establishment is about using manure as it supplies a good, slow release of a number of important nutrients. It also helps with structure and water-holding capacity. That can’t be replaced by applying straight N.”
Once established, there are no hard-and-fast rules about what a five-tonne crop should look like during the autumn. A canopy thick enough to stave off pigeon damage, but kept sufficiently in check, should be the aim. It’s early spring when the management starts in earnest.
“The biggest killer of yield is nitrogen,” says Mr Marr. “Apply too much and the canopy grows too thick, blocking out light to the leaves. The flower is a wonderful reflector. It should be used to bring light down to the leaves as these are five times more efficient at converting it into yield than the pods.”
The aim is for a green area index (GAI) of 3.5 before the onset of stem extension in March. “You need 175kgN/ha to get to 3.5, made up of N in the soil, N in the crop and any bagged N you apply.”
N-Min testing tells you the N in the soil, while there’s 50kgN/ha in your crop for every unit of GAI.
Plant population is also crucial. The aim is for 20-25/sq m by March for hybrids or 30-35 sq m for conventional varieties, says Mr Marr. “You want to end up with a good thick main raceme with plenty of laterals.”
Plant too thick and the crop puts out few laterals, relying on the main raceme to deliver 90% of the yield.
A five-tonne crop needs to be clean, insists Lincolnshire AICC agronomist Ruth East.
“A healthy crop looks after itself and delivers N efficiently. You always get money back on a good fungicide programme,” she says.
This starts with prothioconazole or difenaconazole for phoma and light leaf spot in autumn. Metconazole is a better choice if crop growth needs controlling.
At early stem extension in mid-March, another growth regulatory application may be needed or a high rate of tebuconazole. Mid-flowering the attention turns to sclerotinia and alternaria, and Ms East recommends prothioconazole mixed with azoxystrobin again.
“If you’re lucky you’ll get three weeks out of that. If flowering starts early or it’s a wet spring, you’ll need a third spring spray.”
See our dedicated area for the High 5 OSR Challenge