| Abstrakt: |
Macadamia growers have responded to increasing soil acidity in plantations by applying ameliorants, but optimum pH for production has not been identified. The effects of lime applications on the growth, yield and leaf composition of macadamia (Macadamia integrifolia Maiden and Betch) trees were investigated at each of two sites (Pomona and Cootharaba) with acidic sandy soils in south-east Queensland. Trees at the Pomona 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 site. 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 and Cootharaba sites, respectively. with a concomitant range in soil Ca and A1 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 acidity. However, yields from treatments with pH values greater than 5.5 tended to be lower than those with more acidic pH values, suggesting that overliming may adversely affect long-term productivity. High lime rates also resulted in a marked reduction in the number of proteoid roots. At the Cootharaba site, nitrogen treatments significantly (P < 0.05) increased nut-in-shell yield despite the juvenile growth stage of the trees precluding nut yield until the 1993 season. Although lime applications at the Cootharaba site resulted in some increase in leaf Ca concentrations, treatments at the Pomona site, with older trees, had little effect on leaf nutrient composition. |
