The effect of level and timing of nitrogen (N) fertilizer application on grain yield (YLD), grain protein (GPC), and breadmaking ability of four hard red spring wheat cultivars and on soil residual nitrate was investigated. Nitrogen fertility caused an increase in YLD, lodging, several yield components, GPC, and breadmaking quality and caused a reduction in N harvest index and grain ash, and N use efficiency (NUE) resulting in an increase in soil residual NO$ sb3$-N. Split N application reduced lodging, tillers and spikes m$ sp{-2}$ and caused an increase in grain weight, GPC, loaf volume and NUE. Grain yield increases were largely due to increases in the grain spike$ sp{-1}$ and tillers n$ sp{-2}$. Absolute protein content was found to be critical in determining GPC. Cultivars showed plastic responses to N. Despite its high YLD and flour yield, Hege 155-85 may be risky to produce because of its high dependence on N. Mineralization of N occurred during winter. Marked differences existed between the sites.

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