Amounts of spring nitrogen (N) fertilizer (0–240 kg/ha),
combined with three timing treatments
(single, divided early or divided late), were tested at 14 sites in England
and Wales between 1984 and
1988 to determine the optimum fertilizer N requirement for winter oats.
The trials were superimposed
on commercial crops of the cultivars Pennal (9 sites) or Peniarth (5 sites).
Optimum amounts of N
ranged from nil to 202 kg/ha (mean 119) and optimum yields varied between
5·8 and 9·9 t/ha (mean
7·3). Much (c. 60%) of the inter-site variation in N optimum
was explained by differences in soil N
supply, as indicated by N offtake in the grain at nil applied N. Mean yield
differences between single
and early (+0·08 t/ha) or late (−0·04 t/ha)
divided dressings were slight, although significant
(P<0·05) but inconsistent yield effects were obtained
from early N at two sites and late N at three sites.
Lodging occurred at 11 of the 12 sites where lodging scores were recorded
and always increased
significantly (P<0·05) with applied N. The amount of
crop lodging at N optimum was, on an area
basis, <50% at nine of the sites. The overall extent of site lodging
was also influenced by soil N
fertility and hence inversely related to N optimum. However, multiple regression,
using site lodging
as well as soil N supply, only accounted for slightly more (65%) of the
variation in N optimum, which
suggests that lodging was not a major limiting factor. Lodging was unexpectedly
less from early N
(mean 43%), but more from late N (53%) divided dressings, compared with
a single N dressing
(49%). Early N reduced lodging significantly (P<0·05)
at four sites, although the actual reduction
was only large at one site where early N also increased yield significantly
(+0·57 t/ha).
Grain N concentrations increased significantly (P<0·05)
with applied N, on average by 0·12% per
40 kg/ha N increment. Timing effects on grain N concentration were
very small, with mean values
of 1·94, 1·91 and 1·96%N respectively from single,
early and late divided dressings. Apparent
recovery in grain of fertilizer N at the optimum amount ranged from 13
to 57% (mean 37), with better
N recovery at the more yield-responsive sites. Changes in mean grain weight
due to the amount and
timing of fertilizer N were small, with an average reduction of 0·6
mg/grain per 40 kg/ha N applied.
The adverse effects of N fertilizer on grain quality were slight and unlikely
to have commercial
significance. The agronomic implications of these results on the N fertilization
of winter oats are
discussed.