RESPONSIVENESS OF BARLEY CULTIVARS TO NITROGEN-FERTILIZER

Genotypic differences in responses to nitrogen (N) fertiliser of 6 cul tivars of barley (Clipper, Stirling, Weeah, Schooner, Chebec, Skiff) g rown at 8 different rates of N were examined in 2 seasons. Measurement s of vegetative growth, N content, grain yield, grain protein concentr ation (GPC) and yield components were taken to identify traits that ma y contribute to high yield responsiveness. The optimum rates of N for dry matter production at (DM(ee)) 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 (N-opt) 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 N-opt for the semi-dwarf cultivar Skiff was 71 kg N/ha and it tended to show the greatest yield response to N. It produc ed 19 kernels/g DM(ee) compared with 15-17 kernels/g DM(ee) in the oth er cultivars. Unlike most other cultivars, Skiff's yield was consisten tly and positively correlated with ears/m(2); Stirling was the only ot her cultivar to show a similar relationship. However, the average kern el weight of Skiff was up to 5 mg lower than that of Clipper, Weeah an d Schooner, and varied more than these cultivars between sites, sugges ting that consistent grain size may be a problem in this cultivar. By comparison, Clipper and Schooner had lower N-opt(51 kg/ha) and a less variable kernel weight. There were no signs of differences in GPC of t he 6 cultivars used here at 3 N-responsive sites. Adding N increased G PC up to the highest rate of N and the responses were generally linear , but GPC at N exceeded the upper limit for malting quality of 11.8% a ll 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 experime nts showed that the N rates for optimum yields varied considerably amo ng cultivars, but applying rates to achieve maximum yields may cause G PC to exceed the maximum value for malting barley. The use of semi-dwa rf cultivars, such as Skiff, which are very responsive to N, can provi de some leeway in the choice of N, but there may be a trade-off in qua lity associated with reduced grain size.