8th INTERNATIONAL WHEAT CONFERENCE

Nitrogen use efficiency: Nitrogen accumulation (kg N/ha) by anthesis tended to increase
with crop heights upto around 80cm, but this was only evident when adjustment had
been made to the data for the delaying effect of Rht alleles on time to anthesis. Dwarfing
was also associated with reduced N uptake after anthesis. All Rht alleles reduced N
utilization efficiency (NUtE, kg DM/kg N) for above ground biomass. There was no clear
relationship between crop height and the N apparently remobilized from the vegetation
at anthesis to the grain and maturity. NHI and NUtE to produce grain (NUtE g ; kg grain
DM /kg biomass N) reached maxima at crop heights around 80cm. Overall nitrogen-use
efficiency (NUE, kg grain DM/kg available N) necessarily followed the grain yield response,
peaking at 24 and 19 kg DM/kg N in C and O respectively. N recovery in the grain
(kg grain N/kg available N) peaked at 0.55 and 0.35 in C and O respectively. Low values
in O were associated with significant competition from weeds. NUtE of the grain (1/
grain N concentration) peaked in C at around 80cm, but no peak was evident in O, where
increases were apparent to 120cm. Empirically, grain DM yield was mostly a function of
grain N yield (or vice versa), rather than grain NUtE. There was no consistent effect of
Rht on N/grain so NUE and several of its components were related to grain numbers/
m 2 . Ppd-D1a shortened the time to anthesis, and consequently reduced pre-anthesis N
uptake. There was, however, a compensatory increase in post-anthesis uptake. Other than
for these effects, Ppd-D1a did not have a large influence on NUE and its components.
In the Mercia background, Rht-D1b and Rht8c+Ppd-D1a had similar heights, NUtE for
biomass and grain, NUtE g , NHI and recoveries of N in the grain.
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