EVIDENCE FOR DIFFERENCES BETWEEN CULTIVARS IN RESPONSIVENESS OF WHEAT TO APPLIED NITROGEN

Three cultivars of wheat were grown using five levels of applied nitrogen (N) fertilizer at five locations in the central wheatbelt of Western Australia during 1986, 1987 and 1988. The cultivars were Gamenya (old, tall), Gutha (new, tall) and Aroona (new, semi-dwarf). The aim of the experiments was to determine if the newer cultivars responded more to applied N fertilizer than the older ones. At 10 out of 15 sites there was a yield increase to applied N. The semi-dwarf cultivar Aroona out-yielded the two tall cultivars and responded more to added N at 6 of the 15 sites. The average initial response to applied N at these six sites was 16, 18 and 31 kg of grain per kg of N applied for Gamenya, Gutha and Aroona. Aroona's increased initial response to applied N was not evident at five of the sites that received less than 250 mm of rainfall during the growing season. The increased responsiveness of Aroona was associated with a greater apparent net uptake efficiency, a larger concentration of N in the tops, the production of more ears and kernels per unit area at larger concentrations of N in the tops, and an ability to maintain kernel size at the larger kernel numbers produced by an increased N supply.