Get out into oilseed rape crops now and analyse crop structure and rooting, Masstock technical manager David Langton advised growers attending the firm’s Agrifocus open day in Wiltshire.
“Getting better yields from oilseed rape is all about getting the right canopy.”
But he said too many growers were growing too much canopy, partly because of too high seed rates and the unnecessary use of nitrogen.
Typically, the canopy should remain open enough to allow light to get down to the lower leaves and pods, he said.
But all too often the canopy was too thick.
“For 80% of the year all you are doing is growing a canopy to catch sunlight to convert into yield.
“Leaves photosynthesise twice as efficiently as pods, so you need the canopy to be open enough to get light down to the bottom leaves as well as the pods.”
An easy way to judge whether your canopy was efficient was to dig some plants and check to see whether plants were well branched or just single raceme plants, he suggested.
The latter was characteristic of too thick a canopy.
“The smaller tillers are consuming sunlight and nutrients, but don’t really turn it into yield.”
The first step to establishing the right canopy was through the correct seed rate.
Seed rates were typically 80-100/sq m.
“It’s too much.”
But no specific advice about seed rates could be given, he said.
“It has to be decided on the day depending on conditions.”
Soil type, establishment technique and likely establishment success all had to be taken into account.
Notice should be taken of the German desire to restrict stem extension during winter to maximise rooting.
“You need a good root structure.
Where you have better rooted plants you get better yields.
They’re also more resistant to stem canker and lodging.”
Again the advice was to examine this year’s root structure.
“Roots that go out sideways won’t have good access to soil nutrients, which is important now at the key pod fill timing.”
Applying spring nitrogen unnecessarily was a mistake growers made that contributed to poor canopies.
“It is all about tailoring nitrogen inputs – timing and rate-wise – to the crops.”
That could mean applying less nitrogen to restrict excessive canopy growth, he said.
“Look at Continental Europe, where the cold weather restricts canopy growth.
We can’t do that in southern England because of our temperatures, so we need to do it by manipulating with growth regulator and nitrogen.”
This season’s crops had been helped by the colder and dry spring, he suggested.
“Crops went backwards.”
It promised better yields, he said.
“Look back at the yields in the last two seasons when we’ve had dry springs.
Nationally, they have been 0.75t/ha ahead of when we have had a more growy spring like 2001 or 2005.
“If you manage the canopy right you can unlock the genetic potential of the crop,” he concluded.