Hybrid oilseed rape in need of nitrogen now
Hybrid oilseed rape in need of nitrogen now
By Louise Impey
DO not delay nitrogen applications to hybrid oilseed rape which has started re-growing earlier than normal this year, urges breeder CPB Twyford.
"We have had a shorter than usual period of winter dormancy, which is creating a dilemma for growers," says CPBs agronomy services manager Kerry Barnes. "Usually they put on the first fertiliser as soon as they see signs of spring growth. They are wondering whether now is too early."
Winter leaching and poor rooting also mean extra nitrogen is likely to be needed to meet full yield potential, advises head of oilseeds breeding Liz Williams. A 5t/ha crop needs 300kg/ha of nitrogen from bag and soil reserves combined, she advises.
"Soils have poor structure and waterlogging has occurred, so there is less nitrogen in the soil than normal. And as it is important that nitrogen is available to the plant as soon as it starts to grow after winter dormancy, growers need to take action very quickly."
Without additional nutrients plants continue to develop, which can cause premature stem extension, bud development and flowering, says Ms Williams. "An early nitrogen application will help by encouraging a more gradual development, delaying flowering until the frost risk is reduced."
Rooting is also an issue, with purple patches showing in some crops where waterlogging has removed nitrogen and slowed root growth. Compaction is showing as a legacy of the wet 1998 harvest. But provided action is taken soon symptoms need not cause alarm, she says.
But not all crops are the same. Those drilled before the end of August are generally more advanced than those that went into colder seed-beds in September.
Her advice is for all hybrid crops to receive three splits of spring N. Such a little-and-often approach will ensure poorly rooted crops can take up the N. It will also reduce leaching risks where large total bagged N rates are required.
For backward crops put on up to a third of the total N where conditions are considered poor, or 100kg/ha, as soon as field conditions allow, she advises. The entire sulphur requirement should go on, too. That should be at least 32kg/ha of S or 80kg/ha as SO3. Without sufficient sulphur crops are unable to fully utilise high nitrogen rates, Ms Williams notes.
The rest of the N should go on in equal splits by the green bud stage.
Advanced crops should get the same treatment, but less of a priority. *
HYBRIDRAPE
• Fast spring growth.
• Get first N and all S on early.
• Top N rates may be needed.
• Phoma control still worthwhile.