MINERAL-NUTRITION OF SLASH PINE IN SUBTROPICAL AUSTRALIA .1. STAND GROWTH-RESPONSE TO FERTILIZATION

Fertilization at plantation establishment and later age is often required to maximize stand growth of slash pine (Pinus elliottii) in subtropical Australia. A field experiment was conducted to examine stand growth response of slash pine in the first 11.5 years of plantation following (I) initial fertilization at plantation establishment with phosphorus (P) at 11, 22, 45 and 90 kg P ha(-1) which were either banded or broadcast in the presence or absence of basal fertilizers containing 50 kg nitrogen (N) ha(-1), 50 kg potassium (K) ha(-1) and 5 kg copper (Cu) ha(-1) and (2) additional application of 40 kg P ha(-1) at age 10 years. The initial P fertilization significantly increased the stand growth in the first 9.6 years. The P banded application was more effective in improving the stand growth than the P broadcast application. Application of the N, K and Cu basal fertilizers did not affect the stand growth. Overall, 53-73% of the variation in basal area and volume growth in the first 9.6 years was explained by the initial P fertilization, indicating that P deficiency was the major factor limiting the stand growth under the experimental conditions. Optimum plantation age, at which the maximum periodical annual increment (PAI) of basal area was obtained, increased from age 10.9 to 12 years when the initial P rate increased from 11 to 90 kg P ha(-1). Application of additional 40 kg P ha(-1) at age IO years resulted in a further improvement in the stand growth at age 11.5 years. With 66% of the variation in basal area PAI between ages 9.6 and 11.5 years, 50% was explained by the initial P fertilization and 16% by the additional P applied at age 10 years. Similarly, 51% and 12% of the variation in volume PAI were attributed to the initial P fertilization and the additional P application, respectively. This highlights the need of refertilization with P on some established stands of slash pine at later ages.