Timing of nitrogen application to macadamias. 1. Tree nitrogen status and vegetative growth

Abstract

Nitrogen (690 g/tree.annum) was applied to 12-year-old macadamia (Macadamia integrifoloia Maiden and Betche) trees in subtropical Queensland (lat. 26¦S.) at either pre-floral initiation, inflorescence development, premature nut drop or at the oil accumulation stage. Control trees received a total of 230 g of nitrogen (N) split into equal monthly applications. Leaf N concentrations in May (vegetative and reproductive dormancy) was lower in control trees (approx. 1.2%), which were visually N-deficient during winter and spring. Leaf N concentrations of all other treatments were approx. 1.3-1.4% N and leaves remained a healthy green colour throughout the year. Low N status in control trees suppressed vegetative growth (indicated by changes in trunk girth, tree height and canopy volume), effectively manipulating the vegetative:reproductive balance in favour-of the latter. The desirability of small, but frequent applications of N fertiliser to macadamias is indicated, although the optimum rate is likely to be greater than that applied to control trees in this study. It is suggested that determining tree N requirements using standard leaf nutrient levels should not be done in isolation. Tree health and vegetative growth in relation to yield, and time of sampling, particularly in relation to time of application of N and flushing peaks, should also be considered.