Summary. Genotypic differences in responses to nitrogen
(N) fertiliser of 6 cultivars of barley (Clipper, Stirling, Weeah, Schooner,
Chebec, Skiff) grown at 8 different rates of N were examined in 2 seasons.
Measurements of vegetative growth, N content, grain yield, grain protein
concentration (GPC) and yield components were taken to identify traits that
may contribute to high yield responsiveness.
The optimum rates of N for dry matter production at ear emergence
(DMee) were greater than 80 kg N/ha for all
cultivars and often growth increased up to 105 kg N/ha. Optimum rates of N
for grain yield (Nopt) were lower and ranged, on
average, from 50 kg N/ha for Clipper to 96 kg N/ha for Chebec. The
initial response to N varied from 13–14 kg/kg N in Chebec, Weeah and
Schooner, to 36 kg/kg N in Skiff.
The Nopt for the semi-dwarf cultivar Skiff was 71 kg
N/ha and it tended to show the greatest yield response to N. It produced
19 kernels/g DMee, compared with 15–17
kernels/g DMee in the other cultivars. Unlike most
other cultivars, Skiff’s yield was consistently and positively
correlated with ears/m2; Stirling was the only other
cultivar to show a similar relationship. However, the average kernel weight of
Skiff was up to 5 mg lower than that of Clipper, Weeah and Schooner, and
varied more than these cultivars between sites, suggesting that consistent
grain size may be a problem in this cultivar. By comparison, Clipper and
Schooner had lower Nopt (51 kg/ha) and a less
variable kernel weight.
There were no signs of differences in GPC of the 6 cultivars used here at 3
N-responsive sites. Adding N increased GPC up to the highest rate of N and the
responses were generally linear, but GPC at Nopt
exceeded the upper limit for malting quality of 11.8% in all cultivars.
Average N rates of between 38 kg N/ha (Schooner) and 58 kg N/ha
(Skiff) were sufficient to raise GPC above 11.8%.
The experiments showed that the N rates for optimum yields varied considerably
among cultivars, but applyi1ng rates to achieve maximum yields may cause GPC
to exceed the maximum value for malting barley. The use of semi-dwarf
cultivars, such as Skiff, which are very responsive to N, can provide some
leeway in the choice of N, but there may be a trade-off in quality associated
with reduced grain size.
Implications of Experimental Design on Predicting Economic Optimum Nitrogen Rates in Rice
