Feeding strong OSR potential
This season’s large autumn oilseed rape crop plants may have concerned growers fearful of over big canopies, but vigorous top growth is indicative of strong rooting that 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 pointed out that nutrients from any leaves that do die-back and drop off over the winter will be recycled by the plants, to drive green leaf development over the spring and summer, but that crops need tailored mnagment now to get them growing well.
Ian highlighted that 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 that 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 N/ha for example, as soon as growing conditions commence, if we are to avoid stressing plants that will affect yields,” Ian commented.
Although timing shouldn’t be changed just because of the canopy size, the rate at the early timing should be adjusted to take this into account, advised Ian (below).
He urged growers to initially assess crop GAI in the autumn, and then again in the spring before making any management decisions.
GAI is an important management guide, but growers shouldn’t get too obsessed with hitting targets per se, he advocated. A review of the original trials data that 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 to 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 that can be managed to develop big leafy plants.”
Crops that have been more backward throughout the 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.
Ian also reminded growers of the importance to hold back some of the N allocation for a late flowering application, which had consistently 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 (above), added that the 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 Toprex to manage the crop architecture to open up the potential of the most efficient green leaves,” James advised.
“Furthermore, Toprex use can synchronise flowering of the crop into a shorter, more intense, period – which reduces the sunlight reflectance and allow more light to reach the green leaf and maximise energy production.”
Norfolk iOSR grower, Chris Eglington (below), reported 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 the winter my fertiliser programme is pretty well set now,” he said. “If I had a poor GAI in the autumn, then the spring GAI would be far more important.
“Taking on board what Ian said, I may have been starving my crop more than I should,and intend to start earlier with a little of the N for the biggest crops," Chris added.
"But totally agree that 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.”