pH dominates Leucadendron 'Safari Sunset' growth

The objectives of the present research were to study the effects of pH, NH4 :NO3 ratio, and P concentration in the nutrient solution on development of Leucadendron R. Br. 'Safari Sunset' [L. salignum Bergius x L. laureolum (La m.) Fourc.]. The experiment was conducted in aero-hydroponic systems and in volved six treatments in a nonfactorial design: two pH levels (5.5 and 7.5) , two P levels (7 and 20 mg L-1), and two NH4:NO3 ratios (60:40 and 25:75). The pH of the root environment was the most important factor controlling g rowth. Root cells were longer in plants grown at pH 5.5 than at pH 7.5, but width was not affected. Altering the NH4:NO3, ratio did not affect develop ment regardless of pH. Increasing the P concentration from 7 to 20 mg.L-1 s ignificantly decreased root fresh weight at the low pH and slightly reduced shoot growth. Nitrogen, P, K, Zn, and Mn concentrations were higher, while that of Fe was lower in plants grown at low pH. Reducing the NH4:NO3, rati o did not affect N concentration but increased P and K concentrations in th e shoots. Increasing the P concentration significantly raised the P content of shoot and root tissues but reduced the content of Fe, Zn, and Mn.