GROWTH AND UPTAKE OF N, P, K AND B BY PINUS-RADIATA D DON IN RESPONSE TO APPLICATIONS OF BORAX

Leader dieback associated with B deficiency in P. radiata D. Don plantations was treated with borax applied at rates of 50, 100 and 150 kg ha-1. This initially increased B in foliage from 5 to 40, 80 and 110-mu-g g-1 respectively, and was followed by a rapid decline and stabilisation at around 25-mu-g g-1 for the duration of the study. Annual fluctuations in foliage B levels were strongly correlated with rainfall during the preceding spring and summer. Uptake of N, P and K increased as a result of applied B and comparison of the distribution of these nutrients in crowns of fertilized and unfertilised trees six years after application indicated continued uptake of these nutrients probably as a result of improved root growth due to B. Foliage concentrations of B like N, P and K, increased in young needles towards the upper crown and this, together with a decline in needle concentrations of B as foliage aged, indicated some redistribution of B from older to new foliage. A limit of 5-mu-g g-1 was found below which little redistribution seems to occur. Application of B prevented further leader dieback, improved apical dominance and height growth and increased volume production by 25 m3 ha-1 at age 8 years. Differences between application rates of B were not significant in terms of growth.