Cool way to grow oil
AHDB research has shown that the duration of seed filling is precisely determined by Growing Day Degrees (GDD) – so effectively the warmer the temperatures the quicker seed filling will shut down, whilst in cool conditions the period can be significantly extended.
At an average temperature of 25°C, seed filling could be over in less than 35 days, whilst at an average temperature of 17°C it could go on for 55 days, reported Syngenta OSR Field Technical Manager, Georgina Wood.
Discussing the effects of the cold, slow start to spring growth with iOSR growers, she said: "Oilseed rape seed fill is likely to start later this year - when temperatures can be expected to be hotter."
"In a short, intense seed fill period you need the maximum photosynthetic activity of the green leaf to feed the seed fill period and maximise oil yield,” she pointed out.
The temperature differential could prove particularly pertinent for growers in the north of England and Scotland, where average GDD temperatures can be three to five degrees lower than the south and eastern counties.
“They have real potential to continue pushing yield for longer with effective canopy management and more important now is green leaf retention," said Georgina (above).
"Including an Amistar application at the later flowering timing, to protect against disease and enhance physiological plant greening, will maintain energy capture for longer,” she advised.
“Managing the effects of summer drought is now outside growers’ control, but they can still influence the negative effects of disease and early desiccation, which have been identified as the key factors that cut short the green leaf period.”
The importance of green leaf for energy production during seed fill cannot be over emphasised, added Georgina. Whilst the seed is only a small part of the overall crop biomass – typically accounting for less than a third of dry matter at harvest – the energy-rich oil it holds equals well over half of the plant’s overall content and ultimately, that's what we're looking to harvest.
“One of the physical limitations of the oilseed rape plant is that it is very poor at reallocating its energy reserves. Unlike wheat, which can remobilise up to half of its biomass reserves into filling grain, the oil content of OSR is 90% generated by photosynthetic energy capture after flowering."
“If the plant doesn’t have the green leaf area exposed to the sun, it will never reach its potential,” she advised.
Growers generally attribute OSR yield losses from crop lodging to problems with combining, whereas in fact most of the lost performance could be due to the lodged crop shading itself and preventing light from reaching the lower green leaf.
See the light fantastic
Earlier season canopy management, through initial seed rates, autumn management and spring PGR use, would have all had a significant contribution in creating the plant structure to make the best use of available sunlight – as well as developing a deep root structure to minimise the impact of summer drought.
Studies by AHDB have shown that half of all OSR crops could be compromised by insufficient rooting depth below 40cm. “Getting the deep soil structure right before planting this autumn will help plants right through to next summer,” advocated Georgina.
However, she also urged growers to consider Clubroot as a cause of poor rooting. Whilst the soil-borne pathogen can cause the characteristic malformation and knurling of roots – often leading to premature plant death – at low levels of infection it could still be having an adverse effect on rooting depth.
“Good establishment conditions and nutrition can help to mask the effects of Clubroot, however, there will be an underlying cost in plant health and its ability to take up moisture and nutrients,” she warned.
“There are now some very good Clubroot resistant varieties, with little or no yield penalty over conventional genetics, which growers in susceptible areas or with a known problem should be looking to utilise.”
Clubroot effects on a conventional variety (left) compared to the rooting of SY Alibaba, from a 2017 farm trial in Hampshire, southern England
Whilst Clubroot had historically been considered a major pathogen in Scotland, where brassicas have been more frequently grown in the rotation and soil conditions have suited it, the problem has been increasingly seen in northern and eastern counties associated with warmer and wetter winters.
The Clubroot resistant variety, SY Alibaba, for example, has resistance to both the P1 and P3 clubroot pathotypes. Yields in trials have been comparable with leading conventional varieties, such as Windozz and Alizze, she reported, as well as showing good phoma resistance and robust LLS scores.