Despite not being able to do anything about the weather, there’s a lot we can learn from the generally disappointing oilseed rape performance of 2016 to improve future crop resilience according to a specialist round table of growers and advisers brought together by leading OSR breeder, DEKALB to review the past season.
Everyone involved agreed that the weather was the key factor behind national yields around 0.5 t/ha down on the five-year average of 3.6t/ha. Specifically, a mild, wet winter which restricted rooting while favouring pests and diseases; a cold, dull spring which held back canopy development and flowering; a very dull but warm June which limited pod filling; and early July heat which brought it to a rapid, premature end .
“Solar radiation in June was 31% down on 2015 at our Winchester iFarm, 27% down at Brackley in Northampton and 21% down at Berwick-upon-Tweed,” reported senior Agrii agronomist, Andrew Richards. “This may help to explain why more northerly crops fared relatively better than those in the south.
“With regular rainfall throughout pod fill, the crops certainly didn’t want for moisture anywhere. But on heavy ground, in particular, this masked poor rooting in the wet winter and cold spring. Which, in turn, restricted the crops’ productive capacity and ability to cope with the sudden heat stress of early July, resulting in very small seeds.
“Under these challenging conditions we saw a much greater spread in performance across our variety trials,” he noted. “In the far better growing season of 2015, there was barely a tonne/ha yield difference between the best and worst performing of the 20+ varieties at our Brackley iFarm. But last season, the difference between DK Exalte at the top and Excalibur at the bottom was well over 2t/ha.”
“Intense pressures from cabbage stem flea beetle in some places – larvae as well as adults – and light leaf spot across the country also played their part last season,” added DEKALB technical specialist Will Vaughan-France. “These and other pests and diseases were favoured by both the warm, wet winter and a spring that prevented crops growing away from them as well as they would otherwise do. With these indirect as well as direct weather effects, we really can’t be surprised they struggled to perform.
“Clearly, there’s nothing we can do about the weather,” he said. “And, equally clearly, every season will bring its own weather challenges. Even so, there’s a lot we can do to put our crops in the best possible position to cope with whatever future growing seasons throw at them.”
The round table identified four key areas for such risk management attention – soils, establishment, nutrition and varieties.
Across Flagleaf Farming’s 430 ha of oilseed rape on a wide variety of soils north of Lincoln, 2016 yields were only 0.2 t/ha below the business’ five year average at 3.7 t/ha. However, manager Jim Beeden saw his better-draining soils delivering 4.2 t/ha against just 3.2 t/ha from less well-drained land.
He and AHDB Huntingdon Monitor Farm host, Russell McKenzie who grows just under 150 ha of OSR each year on heavy clay ground both underlined the importance of investing in drainage and mole ploughing to boost their soils’ capacity to deal with weather extremes.
“Rape is so vulnerable to restricted moisture availability at pod fill that we have to do everything we can to encourage early root development,” stressed Jim. “Continual care and attention to drainage throughout the rotation is vital here, and compaction is something we cannot afford.”
“We’ve found cover crops in the rotation can really help soil structure, as well as improving health and organic matter,” Russell pointed out. “But we know that brassicas in the mix can be a bridge for slugs and flea beetles. So we need to choose and grow our covers carefully.”
Putting sufficient time and effort into establishment is crucial, everyone agreed. Not least because crops that fail to establish well or evenly enough are invariably more vulnerable to weather, pests and diseases.
“Less disturbance and more precision at drilling are our priorities,” explained Russell Mckenzie who employs a range of establishment systems depending on soil conditions. “August is one of the busiest times of our year but we have to make time to get the rape in right, sowing it with the care and attention it needs. And we must understand where and when to stop drilling if the risks become too great.
“Switching from subsoiler seeding to a Vaderstad Rapid with a Rapid Lift toolbar has made all the difference on our heavier land,” Jim Beeden reported. “The seeds go in at a far more consistent depth and with far better seed-to-soil contact. Thanks to the drill’s press wheel, we now only need to roll once after drilling to achieve the good consolidation critical for success.”
As well as allowing Flagleaf Farming to vary seed rates to improve establishment on heavy headlands and other problem areas, drilling enables the team to apply DAP in bands alongside the seed, giving the young seedlings immediate access to nitrogen and phosphate. This is followed by variable rate P&K in the spring to support the rapid increase in nutrient demand as the crop grows away from the winter.
DAP placement with the seed and variable application in the spring are also key components of the OSR regime that delivered an average 3.72 t/ha for Russell McKenzie last season, against his five year average of 4.26 t/ha.
“I’m always disappointed with less than 4t/ha from our rape,” he said. “But 2016 would have given us a lot less than this without the care and attention we put into the crop’s nutrition and other management essentials, including steadily building our soil organic matter levels.”
Long-term studies at the AgriiFocus Technology Centre near Marlborough have confirmed the value of adding organic matter in improving both crop nutrition and soil structure. Andrew Richards explains that they’ve also shown very good responses to spring-applied P and K.
“Evening-up soil indices seems to have been much of the recent focus in phosphate and potash work on most farms,” he observed. “Yet available nutrients at the time the crop most needs them are what really count. So we need to be asking ourselves whether index-based applications every three years are providing us with enough available P and K. In many cases, I suspect, they aren’t.
Modern hybrids were seen as another key element in improving OSR resilience, both for their superior ability to grow away from environmental challenges and the combination of yield-protecting traits they carry.
“Studies with populations of 40-50 flea beetle larva/plant last season showed the best DEKALB hybrids suffered noticeably less main stem loss and stunting than other varieties by virtue of faster growth ahead of the winter and earlier stem elongation in the spring,” revealed Will Vaughan-France.
“As well as their superior ability to compensate, double phoma and strong light leaf spot resistance in our hybrids are also proving to be real advantages in minimising crop setbacks should weather or workloads get in the way of the most-timely spraying. Both these diseases can be especially harmful where conditions don’t allow crops to compensate adequately for the damage they cause.”
“Light leaf spot is our biggest disease worry these days,” said Russell McKenzie. “With a world of difference between 6 and 5 resistance ratings, we won’t touch a variety rated at less than a true 6.0 for light leaf spot.”
“At the same time, we’re looking for phoma scores of 8 or more to give ourselves the greatest leeway in our spraying,” added Jim Beeden. “This allows us to use a single November treatment to target light leaf spot as much as phoma so we keep on top of this increasingly problematic disease from the outset.”
Alongside these key opportunities to minimise the risks of poor growing conditions, the round table also suggested extending the OSR rotation to one in four to reduce pest and disease pressures; using Clearfield varieties to reduce competition from cruciferous weeds, eliminate the need for pre-em herbicides and overcome any vigour-reducing effects of SU residues; and taking advantage of market volatility to secure the best available returns over a 24 month selling period.
At this year’s £320/t, it was pointed out that OSR is generating greater returns before oil bonuses at 3.7 t/ha than 4.5 t/ha did a year ago at £260/t. Despite disappointing yields, therefore, it continues to be one of the best margin-earners for most growers and certainly their preferred cereal break.
“Before the past season, we’d never had a field of rape come in at less than 3.5 t/ha,” said Russell McKenzie. “Flea beetle has definitely built-up since the loss of neonics and we’re seeing worrying resistance to even the best pyrethroids. All of which is taking the fun out of OSR growing. When we do the figures, though, few crops can’t touch it in margin terms, even at 2016 yields. So we won’t be moving away from winter rape in a hurry.
“The crop remains a firm fixture in our rotation too,” Jim Beeden insisted. “It beats the alternatives hands-down in so many ways. And, I’m convinced it will continue to do so as we steadily improving its resilience with the many opportunities open to us.”