Choosing a variety of oilseed rape with the wrong physiology for its planting date, as well as poor soil structure, might have contributed to many of the establishment problems last autumn, says Philip Marr, Masstock’s northern technical manager.
He has spent eight years looking at oilseed rape establishment, assessing 110 varieties for their speed of emergence and development.
The work has led him to categorise varieties into three different drilling windows and choosing the right variety, particularly for late sowings last autumn, was crucial.
“Slow-developing varieties, such as Castille, ES Astrid and NK Bravour, didn’t stand a chance in 2008 if they weren’t drilled by the beginning of September,” he says. This is because they have a greater day degree requirement for the development of a leaf, needing between 125-130 day degrees, he explains.
In contrast, a faster-developing type, such as Excel, requires just 85 day degrees, while Lioness and Excalibur sit between the two extremes at 105 day degrees.
“The other important consideration with oilseed rape is that the root stops growing in length once the flower florets are formed,” says Mr Marr. “Any variety emerged by the end of August has the flower florets in place by December, while those that don’t emerge until October won’t have florets until late January or early February.”
This helps to explain why some crops are struggling now, he believes. “They went in at the end of September into a poor soil structure, the root stopped growing at the end of January and dry spring conditions have restricted nutrient uptake.
“In many cases, the root is just three inches long. They can’t get what the crop needs.”
After floret initiation, leaf development speeds up, continues Mr Marr. “This is why some varieties, for example Excalibur, are very early to flower.”
Hybrid varieties are no different to conventional varieties, he stresses. “There are slow, medium and fast developing hybrids. Flash is a very slow one, Excel is very fast.”
He disagrees that hybrids are better on autumn vigour, pointing out that his trial results on vigour have come to the same conclusion as NIAB’s findings.
“Autumn vigour is all to do with seed size,” he says. “Big seed means faster vigour.”
This year, he drilled Hammer, DK Cabernet, Flash and Excel on the same day. “Those with a higher thousand grain weight of 8-9g emerged six days after drilling. The smaller seeded types, with thousand grain weights of 3-4g took another three days to come through.”
Growers looking for a very vigorous variety need to opt for a big seed, he concludes. “The only disadvantage with these is in a dry autumn they need more moisture to germinate.”
The majority of oilseed rape varieties on the market fit into the early drilling window, says Mr Marr. “That means getting them in by the end of August. It’s a good idea to have a medium variety in the mix, in case drilling gets pushed into September.”
His final point is on pigeons. “Slow developing varieties allow them to land in the crop, as the ground cover isn’t there. If you’re likely to have a problem with pigeons, a fast-developing variety will help.”