AMELIORATION OF COARSE-TEXTURED ACIDIC SOILS USED FOR MACADAMIA PRODUCTION .1. TREE GROWTH, YIELD AND LEAF NUTRIENT COMPOSITION

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.