Flowering N to feed OSR yields
This year’s relatively early and forward oilseed rape crops could be best placed to take advantage of late flowering N applications, according to Syngenta Technical Manager, James Southgate.
Longer post-flowering photosynthetic activity could help to drive yields and oil content as the pods fill, he told iOSR growers. The large green leaf area of vigorous crops would have already taken up a lot of the nutrients applied, so these crops may be best placed to utilise any extra N applied at mid to late flowering.
“Green leaf area is by far the most efficient at converting sunlight into yield, compared to pods or stems," he said.
“Crops that have retained healthy green leaf from Amistar at mid to late-flowering can retain significantly greater green leaf area through the post-flowering period to harvest,” advised James.
He pointed out that there is a strong indication that lack of sunshine in May and June last year – when radiation levels were 30% below the norm – was a primary cause of disappointing OSR yields. “There is no knowing that it will happen again this year, but it does reiterate the importance of maintaining green leaf area for as long as possible to utilise available light,” he said. “Those crops which held on later last year, even for a few days, reported to yield better.”
James highlighted that the greatest benefit in retaining green leaf came from Amistar application at green-bud to early flowering, but there was still a significant effect with later applications from mid-flowering.
“Over recent years we have also seen Sclerotinia coming in towards the end of flowering. The later application of Amistar has given good control of Sclerotinia and other late foliar diseases, such as Alternaria” he advocated.
“The key thing is that, even in the absence of disease, the yield increase from the green leaf retention always pays. However, it is important for growers to get the nutrition right so that the crop can reach its full potential,” James added.
Northamptonshire grower, Ian Matts (below), has retained 40 to 50 kg N/ha of the crop’s allocation for a late flowering top-up. He highlighted that his second top-dressing applications were delayed this season and that crops had moved through growth stages very quickly, hence he cut back the overall rate at that time.
However, that has given greater flexibility in allowance for a flowering foliar N application. “I think there will be a particular benefit this year, due to spring applications going on relatively early and total doses being reasonably low,” said Ian. “If flowering is prolonged, an application later on will help to ensure crops do not run out of steam too early.
“Fungicides applied to keep the crop green for longer will only work to their full potential if the crop is fed sufficiently as well,” he added.
ADAS trials have demonstrated that applying 40 kg N/ha at late flowering timing increased gross output by an average 0.25 t/ha, through the combination of increased seed yield and oil content of seed. Yara has calculated the expected return on investment of around 3:1 over the cost of liquid fertiliser application – worth around £115/ha at this season’s prices.
Wider rows let in light
However, Lincolnshire iOSR grower, Andrew Ward, is not convinced by the post flowering N benefit. In fact, one year he reported yields actually decreased. He argues that moving to wider row plantings and using lower seed rates has created bigger, healthier plants that are well able to grow through to harvest without the need for a foliar feed.
“I'm convinced with the wide 50 cm row concept, and would never go back to conventionally drilled,” he reported.
“We get far more branching and pods per stem with wide rows. Light is able to penetrate through the crop, to the floor contributing to a bigger green leaf area.”
Andrew (below right, pictured with Derbyshire iOSR grower James Chamberlain) added all his fields were looking probably the best OSR he has had for a number of years, with very even, disease free and vigorous plants. Flowering was approximately two-weeks ahead of normal, despite sowing at the same time in late August and early September.
“We have made no change to normal N rate and timings - calculated after carrying out N mins and GAI assessments as crop came out of the winter,” he said, “Crops suffered minimal winter damage and GAI's of 1.6 to 2.3 was up on most years.”
Since the ADAS trials revealed no significant differences with timing around the flowering period - between the onset of flowering and two weeks after the end of flowering - Yara advocates the application can be tank mixed with a fungicide treatment where appropriate.
Syngenta Application Specialist, James Thomas (below), highlighted spraying advice for a tank-mix of Amistar with a foliar N feed should aim to achieve good coverage throughout the crop canopy, but retaining as much spray on the leaf surface and stems as possible.
“We would advocate angled nozzles fitted to alternate facing forwards and backwards along the spray boom. Typically application would be at 200 l/ha water volume – although in really dense crops there may be an advantage of increasing water volume,” advised James.
“However, operators should aim to avoid over wetting leaves that could result in excessive run off.” James advocated slowing down and using an Amistar Nozzle would be a good option.
“In tall oilseed rape crops boom height will have to be raised to maintain even pattern across the target zone, but operators should be aware of the risk of drift,” he warned. “If the crop is variable, they will need to adjust the boom height accordingly.”
James also pointed out that foliar application of nitrogen can result in leaf scorch, particularly in hot or sunny weather, or crops under stress from drought.
“Since the key objective of both the Amistar and the nutrient application is to retain green leaf area, it makes sense to apply in the early morning when plants are least stressed, or the evening when it’s not sunny,” he advised.