Promotion of flowering in Eucalyptus nitens by paclobutrazol was enhanced by nitrogen fertilizer

We examined the effects of nitrogen and phosphorus fertilizer and paclobutrazol on flowering precocity and abundance in Eucalyptus nitens Deane & Maid. Trials to test these effects consisted of a factorial nitrogen by phosphorus experiment replicated on two sites and factorial nitrogen by paclobutrazol experiments conducted separately on reproductively immature and reproductively mature trees. The increase in tree size due to nitrogen fertilization increased the occurrence and abundance of precocious flower buds. However, the increase in tree size alone could not account for the nitrogen effect on flowering, indicating a secondary mechanism of flower induction by nitrogen. The application of both nitrogen fertilizer and paclobutrazol substantially increased the occurrence of precociously flowering trees over that of either treatment applied alone. The efficacy of both paclobutrazol and nitrogen in stimulating the flowering of the reproductively mature trees was affected by soil type, but this effect was overcome through the combination of nitrogen and paclobutrazol. The combination of nitrogen and paclobutrazol also restricted tree growth and combined applications on nitrogen deficient sites will be beneficial in commercial systems for producing eucalypt seed.