February 19, 2014
Manage winter rape with particular precision this spring
Many winter oilseed rape crops are so well grown after the exceptionally mild winter that growers should hold-off on their first spring nitrogen until late March, be sparing in the use of it and apply a good growth regulating fungicide at early stem extension, advises Agrii OSR specialist, Philip Marr. This will ensure both the most productive canopies and greatest standing power.
“Regardless of its inherent lodging resistance, any variety can go over if it is either too dense or puts on excessive top growth at the expense of stem strength or rooting,” he stressed to growers meeting at the company’s new iFarm in Holderness this week (Febuary 17). “Excessive crop density or top growth will also seriously compromise canopy light interception and, with it, yielding ability.
“With the possible exception of low biomass hybrids with the semi-dwarf character, agronomy is a far more important factor in the crop’s canopy structure and standing power than genetics. Which puts the onus on careful agronomy to make the most of the great potential we undoubtedly have in this season’s winter OSR.”
Good establishment and early crop development conditions means the vast majority of winter rapes Mr Marr is seeing across the country this year are well-structured and rooted. Especially so where they were sown at appropriate seed rates, received a good root-stimulating seed dressing and had a timely growth regulating dose of metconazole as part of the autumn fungicide programme.
“Even the most vigorous, rapid autumn developers will have plenty enough anchorage and strength to develop well from relatively high Green Area Indexes of 2.0 or more coming out of the winter,” he reasoned. “To ensure the most productive and robust canopies it will be vital to avoid giving them too much early nitrogen, though. Equally, they’ll need a good inclusion of metconazole in their spring fungicide programme.
“Less forward crops, of which there are also a good number this season, will require more nitrogen early on to develop the most productive canopies. They will also have less need for growth regulating power in their spring fungicide.”
With Agrii iFarms from Exeter to Inverness and South Wales to Kent showing one of the widest-ever ranges in GAIs between varieties in a single season – from less than 0.6 to well over 2.0 – Mr Marr considers it vital that spring nitrogen management, in particular, is carefully matched to specific crop condition. At the same time he urges growers to take full account of soil mineral nitrogen contents which early testing shows are also notably variable from field to field.
“At our Newcastle iFarm, our Nitrogen Calculator shows DK Excellium with a GAI of 2.4 needing just 50 kg N/ha to build the optimum canopy and a 3.5 t/ha yield,” he explains. “With N-Min testing revealing 40 kg/ha of N currently available from the soil, we only need to apply 27 kg/ha of fertiliser N at 55% efficiency. In contrast, Excalibur on the same site with a GAI of 0.6 needs around 190 kg of extra N for the same canopy and base yield.
“Add the extra 90 kg N/ha required by both crops for a yield of 5 t/ha and, at 117 kg/ha, the DK Excellium has a total N fertiliser requirement of less than half the Excalibur. More N applied later may be valuable to support a higher yield with the higher potential hybrid, but putting more than a small amount on early 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 to deceive later do so because they are not managed with sufficient precision to produce the right canopies. With the great variation we see in both crops and soils coming in to the spring this time around, such canopy management precision will be more essential than ever.”