Oilseed rape growers will need to strike a careful balance between strong growth and yield loss this spring as mild growing conditions encourage crop canopies to flourish well ahead of normal size for the time of year.
The warning comes from Adas senior research consultant Pete Berry, who says many of the more vigorous and early maturing varieties, which were drilled in July and August, are further forward than last year.
Some growers have even been reporting confused crops coming into bud or flower already, as a only handful of frosts in January failed to hold growth back.
“There is a risk that the plants will effectively outcompete and shelter each other, blocking sunlight which can affect seed numbers and filling on lower pods, ultimately restricting yields”
Pete Berry, Adas
Mr Berry told Farmers Weekly the biggest risk of the accelerated growth is crop lodging, which can potentially reduce yields by 50%, but he explained that having too big a canopy at current growth stages can cause yield losses of about 0.4t/ha.
“There is a risk that the plants will effectively outcompete and shelter each other, blocking sunlight which can affect seed numbers and filling on lower pods, ultimately restricting yields,” he said.
However, the big canopies mean growers could enjoy a welcome cut to required nitrogen inputs this season, with the unseasonably warm weather also encouraging soil mineralisation.
Dr Berry recommends growers examine crops in February and take a green area index (GAI) reading to calculate any reduction in fertiliser that may be warranted.
Bedfordshire grower and Arable Farmer Focus writer Matt Redman said he is considering altering his canopy management strategy this spring to reflect the taller, thicker crops.
“Crops are about knee-high and have thick canopies, but being so high and thick has helped keep the pigeons off.
“No doubt this will mean some changes to what we do in the spring, easing off the initial nitrogen application at least or delaying it slightly.
“Crops will have a fair bit of nitrogen already so hopefully we can make some savings,” he said.