Successive ‘Beasts from the East’ have hampered oilseed rape growers’ fertiliser plans this year with careful management now needed to try to keep potential yield losses to a minimum. CPM seeks advice.
If ever there was a year to manage your crops by growth stage, this is it.
By Rob Jones
This spring’s icy weather and snow cover, combined with waterlogged land and low soil temperatures are causing real problems for oilseed rape growers desperate to get the most out of the crop.
“It’s turning out to be one of those years where it’s virtually impossible to plan fertiliser applications and fieldwork,” says CF Fertilisers’ arable agronomist Allison Grundy.
“Whilst last year’s warm and dry spring helped many growers achieve excellent yields, this year’s weather has confounded them at every stage. You couldn’t imagine two more contrasting years so far.”
But whilst spring is undoubtedly late, concerns are that crops will romp through the growth stages as the weather warms meaning vigilance will be more critical than ever, she says.
“You need to ignore the calendar, look at your crops and be prepared to change your plans if needs be. If ever there was a year to manage your crops by growth stage, this is it. Crops are variable across the country, with some drilled in mid-Sept still quite small, while others sown a month earlier were starting to develop large canopies. These have definitely taken a hit and been pushed back a bit.”
Many crops have had periods of snow cover followed by soggy, waterlogged soils as it melts.
As a result, many growers who carried out CF N-Min testing in Feb may need to re-evaluate Green Area Index (GAI) to get an accurate foundation for calculating future nitrogen needs, she suggests.
“Soil Nitrogen Supply (SNS) uses an estimate of GAI to ascertain the level of nitrogen already taken up by the plant and then adds this to Soil Mineral Nitrogen (SMN) and Additionally Available Nitrogen (AAN) to give a true picture of nitrogen needs.
“If GAI has gone back a bit, then crops may need a bit more nitrogen applied to make up for this because the nitrogen already contained in the crop makes a significant contribution to the overall SNS,” she explains.
CF business manager Ross Leadbeater is more direct, saying if you can travel safely on the land without causing damage, go for it. “I’m worried about yields this year. Where there was little snow cover, crops definitely got hit hard by the cold weather, with some visibly going backwards. In other cases, when the snow started to melt, the pigeons moved in and they have done a lot of damage to some crops.”
It’s important to be realistic about GAI and reassess where necessary otherwise crops could be nitrogen deficient throughout the growing season, he says.
“Sulphur will be of critical importance too. OSR has a large requirement for sulphur, taking up to 250kg SO3/ha by July in most years. But this year without sufficient sulphur, you just won’t get the levels of nitrogen utilisation efficiency the crops will definitely need.
“My advice is to get your sulphur on early, and if you have a good SNS you can probably hold off the second dressing of straight N until it’s safe to apply it. But if you see an opportunity, don’t miss it – it’s shaping up to be a very difficult year.”
Many crops entered March hungry for nitrogen, although some growers did manage to get some on in between the bouts of cold weather, points out Allison.
Delayed fertiliser and fungicide applications are going to put the pressure on this spring.
“I can understand why growers would be keen to get ahead, but the recovery of these applications by the crop is likely to be a lot less than typical. It’s also likely that nitrogen applied during the very cold, snowy and wet weather has been at risk of surface run off or will have leached down the profile and out of the rooting zone.
“It’s easy to see this in hindsight, but conditions have been so unpredictable making the right decisions has been virtually impossible. In some parts of the country we’ve seen 10oC swings in air temperature within a matter of 24 hours.”
But despite the cold wet weather and concerns about nitrogen availability, analysis of CF N-Min tests conducted during Feb and March shows SNS are nationally a little better than last year, she says.
“Last year, we saw around 10% of samples taken showing SNS levels in the band between 25 – 50kgN/ha, which is pretty low and meant a lot of nitrogen would need to be put on to get decent yields. This year, that same band accounts for only 5% of samples, so SNS levels appear to be higher generally.”
The higher SNS levels could give growers some options with fertiliser timings, she believes. “If you have a high SNS level, there’s a case for delaying early nitrogen as the plant will be able to take what it needs from the soil for the earlier stages of canopy development.”
The real problem will be the reduced window for getting fertiliser on as crops will grow very quickly as the days lengthen and the cold conditions become a memory, says Allison.
“At the end of March and into early April, particularly on the lighter textured soils, crops certainly started to move. On the heavier soils crops take a little longer to get going but don’t tend to run out of steam as the season progresses.
“We recommend using DoubleTop (27N + 30SO3) at the first timing to provide between 50-80kg SO3/ha, or 112kg SO3/ha in circumstances of high deficiency risk, and about 45-72kgN/ha, and hopefully most people will have been able to find a window to do that.
“The issue now is getting on the remaining nitrogen and, depending on what your base SNS was, this will have to be one application as soon as possible or two applications in fairly tight succession.”
Whatever the base SNS, the canopy management principles suggest you need to get 175kgN/ha into the crop by green bud stage. This supply comes from a combination of the SNS and the nitrogen you apply from the bag, she explains.
“This should give you the foundation for a yield of around 3.5t/ha and you’ll need to add a further 30kg N/ha for every additional 0.5t/ha you expect to achieve on top. So if you’re aiming for a final yield of 5.0t/ha, you need to be applying a further 90kgN/ha – equivalent to 260kg/ha Nitram (34.5%N) to achieve it.”
This final application for additional yield needs to be applied at early yellow bud/early flowering, she points out.
“Applying N too late during the flowering period can cause physical damage to the crop and negatively impact on oil content, the later you apply. CF advice is always to apply N before the crop gets into full flowering swing,” says Allison.
2018 may also be remembered as a difficult year for those relying on liquid fertilisers, she believes. “The late spring and the reduced window for optimum fertiliser applications will be manageable for those using solid material, but for liquid users the demand on the sprayer will be extremely difficult to manage.
“It’s not just fertiliser applications that will need to be conducted in a shortened time period this year, but also herbicide treatments and fungicide programmes, so there could be a real bottleneck as the spring develops.”
Whatever you do, you must keep a close eye on the crop, work with your agronomist to manage all crop inputs as effectively as possible and be prepared to be flexible, she points out.
“In a year like this you have to farm by growth stage and be vigilant. A lot can happen in a week so be ready with product and equipment so that you can get on quickly when the opportunity arises.”
Advice for this spring
- Manage crops by growth stage not calendar date.
- Be prepared to re-evaluate GAI if necessary and adjust N rates accordingly.
- Get a first dressing on as soon as the land allows you to travel.
- Don’t forget sulphur.
- If SNS levels are good, consider delaying a second application of N.
Good genes count too
While management of nitrogen rates and timings are of critical importance in optimising canopy development and light capture, how different varieties cope with cold conditions is largely down to genetics, says Michael Farr of breeders DSV.
“The right nutrition and effective use of PGRs where necessary are essential components of good spring management, but much of a crop’s ability to grow quickly and produce the correct plant architecture after a cold unforgiving winter is in-built.
“Many of the hybrids that perform best in cold conditions – Sparrow 45, Dualis and Dariot, for example – have a ‘pre-programmed’ specific burst of growth in early spring to break dormancy and lay the foundation for the best plant structure,” he explains.
Some thinking suggests early flowering could be an increasingly important factor in building yields, as is a relatively short flowering period, he says.
“Early flowering can minimise the threat from pollen beetles and allows a longer period for pod fill. The shorter the flowering period, the less chance there is of valuable light being reflected rather than being used by the leaves and pods to drive growth,” says Michael.
The new varieties Plurax CL and Phoenix CL are good exponents of this thinking, he says. “As well as allowing growers to benefit from the proven advantages of Clearfield technology, they also flower relatively early and have a short to medium flowering duration which goes a long way to explaining why they achieve similar high yields to the best performers on the current Recommended List.
“In addition, they are very winter hardy as they were tested in some of the coldest conditions in Europe. After a growth pause in winter, which allows them to avoid the worst of the frost damage, they produce good canopy development characteristics in spring which provides the ideal foundation for stable yields.”
Even though these characteristics are largely in-built, strong performance in the spring and at flowering can be influenced by appropriate in-field management of crops, he adds.
“In last year’s Yield Enhancement Network (YEN) initiative, a crop of Incentive 45 – one of the most popular varieties chosen by the 53 growers in the project, sown at DSV’s Oxon site – achieved top spot in the trials section with a yield of 5.8t/ha.
“As well as good canopy management, effective control of weed competition and potential diseases can have a profound effect on how much light a plant can absorb and its subsequent yield.”
Sclerotinia can cause significant losses with some reports suggesting crops can lose 50% of their potential yield from the disease, he points out. “Sclerotia occur within the soil profile and those in surface layers germinate in spring when soil temperatures are above 10°C. These produce ascospores which are discharged into the air and land on petals infecting plants.”
The DSV YEN crop was treated with four fungicide sprays in total, with the first two in the autumn followed by one in spring and a final one at petal fall. Different modes of action were used including SDHIs, strobilurins and triazoles, with alternaria and botrytis targeted at petal fall.
“The overall aim is to maximise the total number of seeds produced by the plant, with the 121,000 seeds/m2 achieved by the DSV crop at Wardington being the highest of all crops taking part in the YEN initiative,” he concludes.
