Ra. Stephenson et al., AMELIORATION OF COARSE-TEXTURED ACIDIC SOILS USED FOR MACADAMIA PRODUCTION .1. TREE GROWTH, YIELD AND LEAF NUTRIENT COMPOSITION, Australian Journal of Agricultural Research, 47(1), 1996, pp. 97-107
Macadamia growers have responded to increasing soil acidity in plantat
ions by applying ameliorants, but optimum pH for production has not be
en identified. The effects of lime applications on the growth, yield a
nd leaf composition of macadamia (Macadamia integrifolia Maiden and Be
tch) trees were investigated at each of two sites (Pomona and Coothara
ba) with acidic sandy soils in south-east Queensland. Trees at the Pom
ona site had been established for 6 years whereas, at Cootharaba, the
trees had been recently planted. The effects of annual applications of
nitrogen and nitrogen plus lime were also studied at the Cootharaba s
ite. Tree parameters and soil properties were monitored each year for
5 years after treatment application in 1988. Treatments resulted in pH
(water) values ranging from 4.6 to 7.5 and 4.3 to 6.5 at the Pomona a
nd Cootharaba sites, respectively, with a concomitant range in soil Ca
and Al levels. Despite the wide range in soil properties, lime had no
significant (P < 0.05) effect on nut-in-shell yield in any year, and
the results suggest that macadamia is relatively tolerant of soil acid
ity. However, yields from treatments with pH values greater than 55 te
nded to be lower than those with more acidic pH values, suggesting tha
t overliming may adversely affect long-term productivity. High lime ra
tes also resulted in a marked reduction in the number of proteoid root
s. At the Cootharaba site, nitrogen treatments significantly (P < 0.05
) increased nut-in-shell yield despite the juvenile growth stage of th
e trees precluding nut yield until the 1993 season. Although lime appl
ications at the Cootharaba site resulted in some increase in leaf Ca c
oncentrations, treatments at the Pomona site, with older trees, had li
ttle effect on leaf nutrient composition.