Nitrogen Deficiency Slows Leaf Development and Delays Flowering in Narrow-leafed Lupin

Effects of nitrogen (N) supply on leaf and flower development in Lupinus angustifolius L. cv Merrit were examined in a temperature-controlled glasshouse. Low N supply (0.05 or 0.4 m M N) had little effect on leaf initiation but slowed leaf emergence on the main stem compared with plants receiving high N supply (6.0 or 6.4 m M N), or with symbiotic N 2 -fixation. Plants experiencing transient N deficiency had slower leaf emergence than plants with a continuous supply of 6.4 m M N. Nitrogen supply did not affect the time of floral initiation, which occurred within 4 weeks of sowing, by which time nine to ten leaves had emerged. However, the flowering of low-N plants was delayed by 68 to 220 °C d (i.e. 4–14 d) even though they had fewer leaves. The effect of N deficiency on flowering time was largely a result of slower leaf emergence.