Year × variety means of wheat grain crude protein content
(CP)
and Hagberg falling number (HFN)
surveyed in the UK from 1974 to 1993 were investigated with a residual
maximum
likelihood
(REML) analysis using variety, nitrogen fertilizer application (kg N/ha),
average monthly
temperatures (°C), and total monthly rainfall (mm) as fixed terms,
and year
as a random term.
Annual variety means were weighted according to the inverse of their variances.
The statistical
significance of fixed terms as they were added to the model was evaluated
by
comparing the Wald test
statistic with critical values of chi-squared. CP, except for 1976 which
was
associated with prolonged
drought conditions, was best described with a model combining effects for
variety (P < 0·001),
nitrogen application rate (0·0143, S.E. = 0·00312,
P < 0·001),
July temperature (0·184, S.E. = 0·0582,
P < 0·01) and May rainfall (−0·00952,
S.E. = 0·00233,
P < 0·001). A model describing HFN
combined effects for variety (P < 0·001), August rainfall
(−0·930, S.E. = 0·2579,
P < 0·001) and June
temperature (24·4, S.E. = 7·37,
P < 0·001). These models were
evaluated for describing CP and HFN
of cv. Avalon grown on sandy-loam from 1982 to 1992 at one site. Correlation
coefficients of 0·51
(P = 0·1) and 0·72 (P = 0·012) were
obtained between observed values at this site and those predicted
from the nationally derived models for CP and HFN respectively. Variety
effects
suggested that the
varieties commonly used in the mid 1970s would give higher CP and lower
HFN
than their more
modern counterparts if grown at similar levels of nitrogen and in the same
climatic conditions.