Mineral nutrition of slash pine in subtropical Australia. III. Relationships between foliar P concentration and stand growth

Abstract

Foliar P concentration of slash pine was significantly related to the stand growth in the first 11.5 years. The relationship between foliar P concentration and total stand growth at foliar sampling improved as the plantation aged with coefficient of determination (R2) increasing from 0.14–0.15 at age 3.3 years to 0.56–0.65 at age 9.6 years. However, only 12–18% of the variation in total stand growth was explained by foliar P concentration at age 11.5 years when additional 40 kg P ha−1 was applied to the stands at age 10 years. This suggests that caution should be exercised in interpreting the foliar P concentrations of the established stands which had received application of P fertilizer just prior to foliar sampling. Periodic stand growth was more closely related to the foliar P concentration than total stand growth. Basal area and volume periodic annual increment (PAI) was better related to the foliar P concentration than height PAI.

Optimum foliar P concentration, at which the maximum stand growth was obtained, was between 0.093% and 0.110%. The optimum foliar P concentration for height PAI immediately prior to foliar sampling decreased from 0.097% at age 3.3 years to 0.070% at age 9.6 years. Critical foliar P concentration at age 9.6 years, at which 90% of the maximum basal area growth was obtained, was between 0.066% and 0.070%. Both optimum and critical foliar P concentration might decrease as the plantation aged.