Dramatic differences due to nitrogen timings are showing
up in oilseed rape trials on drought-prone land at the meeting's
host farm.
The first of a range of N dressings on the
GrowHow/
HGCA/
Bayer experiments at Fawley Court Farm, designed to see if
semi-dwarf varieties might need specific N management, had been
applied at the end of February. Manager Mark Wood's first
treatments, 80kg/ha plus sulphur, had not gone on until 12
March.
Dramatic differences were already showing between the trial
treatments which include one with an initial half total dose of
180kg/ha intended to stretch the two varieties -
Excalibur
and semi-dwarf
PR45D03 - to their limits.
"It's amazing how similar they all looked only eight days ago,"
said John Spink, then of ADAS
but now with Eire's
Teagasc.
By contrast the surrounding
Castille
on the mainly sandy loam appeared relatively thin and not far off
flowering. "We didn't have any rain in March, and I think the roots
just haven't found the
Sulphan yet," said Mr Wood.
With hindsight it was easy to suggest that the commercial
dressing should have gone on sooner, said Mr Spink. "But you
wouldn't have expected the whole of March to be dry. The trials
have clearly got hold of the N and we're seeing some massive
responses."
Nevertheless the farm crop still had plenty of potential, and
was certainly more promising than the lush dark green Excalibur
which would eventually receive 360kg/ha of N and so overshoot the
optimum GAI of 3.5 by flowering, he explained.
Despite appearing relatively thin, Mr Wood's fields drilled in
late September were mainly uniform thanks to good establishment.
Only rarely had trials shown any advantage in sowing at the start
rather than the end of September, and good yields were possible
from plant populations as low as 9/sq m (1/sq ft), noted Mr
Spink.
One of team member Innes McEwan's crops, which according to its
GAI (Arable 20 Feb) needed no bag fertiliser, posed a potential
problem with sulphur supply, noted GrowHow's Tom Land.
"We need to get everything else right before knocking back the
N," he said.
Malate sulphur testing suggested Mr McEwan's crop needed
100kg/ha of SO3. In theory that could be supplied by the firm's
Double Top, but applying enough to do so would supply far too
much N, risking an overlarge canopy and reduced yield.
Using kieserite (magnesium sulphate) would be too expensive, so
Mr Land's recommended an alternative. "I'll get into trouble for
saying it, but I'm advising ammonium sulphate."
Using enough to supply most of the necessary sulphur (allowing
for the fact that the field had a history of organic manure use)
would add only 27kg/ha of N. And because fertiliser N is used with
only 60% efficiency that reduced the risk of over-supply, he
explained.
Pre-harvest management
Given the wide range of oilseed rape growth stages within fields
this season growers planning to desiccate should consider treating
patches of different maturity separately, suggested
Syngenta's Iain
Hamilton.
"They may well need to this year."
A key benefit of desiccation was reduced drying costs - a big
issue last harvest, he said. The main choice was between "true
desiccation" via
Reglone (diquat) or "slow death" using glyphosate, as in
Touchdown, for about half the cost.
Each offered specific yield-saving advantages, while swathing,
traditionally a more northern operation, fell somewhere between the
two in terms of speeding harvest.