Boron requirements of macadamia seedlings1

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Abstract
A greenhouse experiment was conducted to determine the internal and external boron (B) requirements of macadamia (Macadamia integrifolia). Ten B levels ranging from 0 to 32 mg B/kg were added to a Typic Hydrandept from Hawaii where commercial plantings of Macadamia have been intense. Visual symptoms, leaf dry weights, and B concentrations in leaves and in soil solutions were monitored periodically to measure plant response to B treatments. Results suggested that the internal B requirement of macadamia is relatively high as compared with other crops. The adequate range is 40 to 100 mg B/kg in leaves. The external requirement is rather modest. Optimum growth was attained at 0.45 mg B/L in soil solution which corresponded to an application rate of approximately 2 kg B/ha for this Andept. Boron toxicity may pose a greater problem than B deficiency because the margin between adequacy and excess is narrow.