It is now well known the key to achieving high oilseed rape yields is to deliver a high number of seeds. And with seed number determined during a two to three week period towards the end of canopy development, the aim must be to maximise photosynthesis during this time, growers attending an Agrovista GrowCrop Gold discussion group meeting at Croft, Darlington, heard.
Technical manager Chris Martin said: “We need to maximise photosynthesis in this period. To do this, we need to maintain the canopy for as long as possible, as the leaves are the most effective part of the plant at photosynthesising.”
He identified a number of factors which play a part in influencing the green area index of oilseed rape plants at this crucial time.
Producing a canopy which is not too big is important in making efficient use of light, allowing for optimal photosynthesis, so nitrogen cannot be applied to early. Instead, the green area index of the crop can be prolonged with late nitrogen applications.
Mr Martin said: “When applying foliar nitrogen at flowering with the sclerotinia spray, we are seeing regular yield responses of 0.3 tonnes per hectare.
“While historically we looked at applying nitrogen to the pod, this meant an extra pass and caused a lot of damage to the crop but also reduced seed oil content. By bringing the application forward, with the sclerotinia spray, we avoid this.”
Initial trials in Germany suggested a limiting factor to seed number is the distance between plants.
Mr Martin said: “If the growing plant is not given enough room, the plant tries to fight for light. In doing so it grows upwards and will not branch to the side. This will not correct itself so it is important to get it right from day one.
“A distance of less than 5cm between plants led to strong competition leading to a yield reduction. Additional work over the last seven years has shown a maximum limit of 15 plants per linear metre should be set.”
While at narrow row spacings this should never become a problem, as row spacings are widened, it is important to cut seed rates back to avoid exceeding 15 plants per linear metre, said Mr Martin.
There are also weed control considerations. When a developing oilseed rape plant touches a neighbouring weed, it fails to branch out so it is best to remove competition early by applying well-timed pre-emergence and early post emergence sprays, he added.
Another key finding has been the importance of unrestricted root growth. To fill seeds, the filling period needs to be as long as possible. Inadequate moisture and nutrients can cause the filling period to become shortened, and so active root growth is crucial.
The project has revealed a number of factors which have the potential to limit root growth.
“Removing compaction is key in order to ensure roots can retrieve nutrients for seed fill. As well as this, gaining good seed-to-soil contact is important in ensuring optimal germination. Therefore double rolling in opposite directions can be crucial in one-pass systems,” said Mr Martin.
He also identified soil nutrients as an important root growth factor. “Every year we have seen a root growth response to soil nitrogen and phosphate. Applying phosphate is important as it gives roots energy to grow and search for natural nutrients.”
New products are proving beneficial in increasing root activity, including new fungicides such as penthiopyrad and biostimulants such as Terra-Sorb
“Now we have penthiopyrad, the first specific SDHI for OSR, we are seeing a yield benefit through rooting not just due to fungal protection,” said Mr Martin.
Growing oilseed alongside various companion plants produced better establishment year on year compared to OSR grown on its own in Agrovista trials.
Mr Martin suggested this could be because the companion plants help produce a better microclimate which aids plant growth, or the reduction of pests associated with growing companion crops.
“We have seen a massive reduction in slug activity where companion plants have been grown. Nobody really knows why although some suggest there is simply more biomass to eat which is potentially more palatable than the OSR leaves,” he said.
Perhaps more importantly, is the benefits companion crops have shown underground. As well as improving soil structure, trials have indicated OSR rooting is improved when companion crops are grown.
Mr Martin said: “There has been around a 25 per cent increase in OSR rooting where we have got companion crops. This is over three years.
“Berseem clover has proved particularly good at breaking through compaction layers and providing a path for OSR roots to follow. We are seeing this consistently in the field.”
Additionally, companion crops are good at trapping nitrogen in a form that is not going to be lost to the atmosphere or leach into watercourses. In the spring, this nitrogen becomes available to the crop.
“We are seeing around 30kg per hectare being trapped over the winter,” said Mr Martin.
Companion crop trials have led to a range of yield improvements depending on the site and the nature of the growing season. The biggest response has been on more challenging sites, he added.
“The Croft trial site saw only a 0.1 tonne per hectare yield increase; however it has been a fantastic year and OSR crops have not needed much help. In more challenging areas, we have seen well over 1 tonne per hectare improvements,” said Mr Martin.