The new season iOSR initiative is underway, with the first meeting of Syngenta’s oilseed rape growers group having taken place at Sutton Estates, Lincolnshire.
This season’s predominantly big oilseed rape crop plants may be concerning for growers fearful as winter approaches, but vigorous top growth is indicative of strong rooting which could prove the foundation for good yield potential, according to Yara Consultant and agronomist Ian Matts.
Discussing nutrition plans with the Syngenta iOSR grower group, he said nutrients from leaves which do die-back and drop off over winter will be recycled by the plants, to drive green leaf development over spring and summer.
Host for the November iOSR Group meeting Chris Baylis, head of farming for Sutton Estates, based at Stainton le Vale, Lincoln, said the combination of good establishment conditions and growing 100% hybrid varieties had resulted in strong autumn growth.
With the farm’s gradual improvement in soil conditions, the reliability of establishment techniques and the early autumn hybrid vigour, Mr Baylis believes there is scope to reduce the seed rate even further from this season’s 45 seeds/sq.m.In October he had already applied an autumn triazole fungicide, intended as much to suppress growth as to prevent disease.
The application rate had been tailored to the size of different crops, based on 25gof tebuconazole per true leaf emerged. “We will certainly be looking closely at spring nutrition to keep the crop growing. The farm has relatively high pH levels, so there is the risk of lock up and availability,” he added.
“We are doing regular tissue tests to build up a picture of the crop’s requirement over time. That can be linked to satellite imaging and N sensor readings of crop health.
He urged growers to assess crop GAI in autumn, and then again in spring before making any management decisions. GAI is an important management guide, but growers should not get too obsessed with hitting targets per se, he advocated.
A review of the original trials data which set the optimum GAI at 3.5, revealed the highest yield was from a crop with a GAI of 5.5, with crops from GAI 2-5.5 all capable of performing well. “Individual plant structure is more important; a dense plant population with masses of tall, thin stems may have a desirable GAI, but is far less efficient and will be less productive than a lower count which can be managed to develop big leafy plants.”
Mr Matts highlighted the natural inclination may be to delay spring fertiliser applications on the larger and more forward crops, in an effort to restrict the target GAI to 3.5. “However, they are the crops which are likely to get growing first when conditions warm up,” he said. “And they are most likely to have already used up any available N in producing the bigger plants.
“That makes it more important to give them an early spring application, of 20-30kg nitrogen/hectare for example, as soon as growing conditions commence, if we are to avoid stressing plants which will affect yields.”
Although timing should not be changed just because of the canopy size, the rate at the early timing should be adjusted to take this into account.
Crops which have been more backward throughout autumn and winter – particularly in drier eastern counties this season, where autumn growth was restricted by dry conditions and insect pest damage – will also require the early N application as soon as conditions warm up for growth, but may need higher rates of application to stimulate rapid development.
Once crops get motoring, they can be using up to 2.5kg N/ha per day to support green leaf growth. Mr Matts also reminded growers of the importance to hold back some of the N allocation for a late flowering application, which had consistently been shown to increase yields.
Although the oil content (as a percentage) is generally decreased with increasing N application, but this is outweighed by a larger increase in yield, he pointed out.
Syngenta technical manager James Southgate added that spring nutrition timing and application rate to manage crop growth should be allied to the use of Toprex to adjust crop architecture to make most efficient use of inputs and sunlight.
“Oilseed rape performance suffered severely with the low levels of sunlight through the crucial June pod fill period – with light for photosynthesis down by more than 30% over the month,” he reported.
“It emphasised the crucial importance of managing the crop architecture to open up the potential of the most efficient green leaves,” he said.
“Furthermore, Toprex use can synchronise flowering of the crop into a shorter, more intense, period – which reduces the sunlight reflectance and allows more light to reach the green leaf and maximise energy production.”
Norfolk iOSR grower Chris Eglington said his crops were as big as they have ever been going into winter.
“They are certainly the biggest in terms of GAI since we’ve been sowing at ultralow seed rates. “I think autumn GAI is a good base to start from, so I’ve made my visual assessment of the crop; whatever happens over winter my fertiliser programme is pretty well set now,” he said. “If I had a poor GAI in autumn, then spring GAI would be far more important.“
Taking on board what Ian said, I may have been starving my crop more than I should, but totally agree a good proportion of the nitrogen should be left for later application, which for us has been going through with solid at the last possible moment and then applying liquid.”
High humidity and almost permanently wet leaves in a dense crop canopy could create the ideal conditions for light leaf spot (LLS) development in late autumn, warned Frontier agronomist Jeremy Ruff.
Where growers had been targeting phoma with early autumn fungicide applications, as the season progresses into November, greater emphasis should be on bolstering LLS protection, typically adding tebuconazole to Plover treatments.
“There is little or no curative activity for LLS, so the priority has to be on early prevention to stop disease getting established,” he advised.
“Once it’s in a dense crop it will continue to cycle and develop, especially over another mild winter.” Mr Ruff pointed out that while varietal resistance may help slow development of disease within the crop, plants are still susceptible and will be using energy to fight infection – which is better dealt with by a fungicide programme.
“With phoma, the resistance rating is based on a score of stem cankers in spring, not leaf infection in autumn; growers should be using varietal resistance as a guide for managing crops and prioritising treatments.”
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