Despite the lack of evidence for a critical level of leaf nitrogen in
macadamia, fertiliser management has been largely based on tentative s
tandards for high yielding trees. Trees on a lower plane of nitrogen n
utrition, however, produced higher yields of good quality nuts. This s
tudy was therefore carried out to establish the relationship between y
ield and nitrogen status of trees. Three rates of nitrogen fertiliser
(0.5, 1.5 and 2.5 kg urea/tree.year; 230, 690 and 1150 g nitrogen resp
ectively) were applied to macadamia trees in 1 of 5 application strate
gies: 1 application in April (floral initiation); 2 applications, one
in April and one in June (inflorescence development); 3 applications,
April, June and November (rapid nut growth and premature nut drop); 4
applications, April, June, November and January (oil accumulation); an
d 12 monthly split applications. Multiple applications were all equal
in size. The association between high yields and low nitrogen status w
as confirmed. In some, but not all, years, yield was negatively correl
ated with leaf nitrogen, accounting for 47 and 59% of the variation in
yield of commercially acceptable nuts (>19 mm diameter) in 1991 and 1
993, respectively. It is therefore recommended that the standard for l
eaf nitrogen in macadamia be lowered from 1.4-1.5 to 1.3% under Austra
lian conditions. These results raise concerns at the current trend for
leaf nitrogen to be as high as 1.8%. It would be prudent to cease nit
rogen applications on at least a small experimental block until leaf n
itrogen declined to 1.3% and then maintain this level for at least 3 y
ears and monitor yields.