Agrii OSR specialist, Philip Marr.
Many winter oilseed rape crops are so wellgrown after the exceptionally mild winter that growers should hold-off on theirfirst spring nitrogen until late March, be sparing in the use of it and apply agood growth regulating fungicide at early stem extension, advises Agrii OSRspecialist, Philip Marr. This will ensure both the most productive canopies andgreatest standing power.
Regardless of its inherent lodging resistance, any variety can go over if itis either too dense or puts on excessive top growth at the expense of stemstrength or rooting, he stressed to growers meeting at the companys new iFarmin Holderness this week (February 17). Excessive crop density or top growthwill also seriously compromise canopy light interception and, with it, yieldingability.
With the possible exception of low biomasshybrids with the semi-dwarf character, agronomy is a far more important factorin the crops canopy structure and standing power than genetics. Which puts theonus on careful agronomy to make the most of the great potential we undoubtedlyhave in this seasons winter OSR.
Good establishment and early crop development conditions means the vastmajority of winter rapes Mr Marr is seeing across the country this year arewell-structured and rooted. Especially so where they were sown at appropriateseed rates, received a good root-stimulating seed dressing and had a timely growth regulating dose ofmetconazole as part of the autumn fungicide programme.
Even the most vigorous, rapid autumndevelopers will have plenty enough anchorage and strength to develop well fromrelatively high Green Area Indexes of 2.0 or more coming out of the winter, hereasoned. To ensure the most productive and robust canopies it will be vitalto avoid giving them too much early nitrogen, though. Equally, theyll need agood inclusion of metconazole in their spring fungicide programme.
Lessforward crops, of which there are also a good number this season, will requiremore nitrogen early on to develop the most productive canopies. They will alsohave less need for growth regulating power in their spring fungicide.
WithAgrii iFarms from Exeter to Inverness and South Wales to Kent showing one ofthe widest-ever ranges in GAIs between varieties in a single season from lessthan 0.6 to well over 2.0 Mr Marrconsiders it vital that spring nitrogen management, in particular, is carefullymatched to specific crop condition. At the same time he urges growers to takefull account of soil mineral nitrogen contents which early testing shows arealso notably variable from field to field.
At our Newcastle iFarm, our Nitrogen Calculator shows DK Excellium with a GAIof 2.4 needing just 50 kg N/ha to build the optimum canopy and a 3.5 t/hayield, he explains. With N-Min testingrevealing 40 kg/ha of N currently available from the soil, we only need toapply 27 kg/ha of fertiliser N at 55% efficiency. In contrast, Excalibur on thesame site with a GAI of 0.6 needs around 190 kg of extra N for the same canopyand base yield.
Add the extra 90 kg N/ha required by both crops for a yield of 5 t/ha and, at117 kg/ha, the DK Excellium has a total N fertiliser requirement of less thanhalf the Excalibur. More N applied later may be valuable to support a higheryield with the higher potential hybrid, but putting more than a small amount onearly could do more harm than good, as well as being extremely wasteful.
All too often, in my experience, winter rape crops that flatter early only todeceive later do so because they are not managed with sufficient precision toproduce the right canopies. With the great variation we see in both crops andsoils coming in to the spring this time around, such canopy managementprecision will be more essential than ever.