Principles and practice of foliar analysis as a basis for crop-logging in pine plantations

Abstract

Progress towards the introduction of crop-logging as a management tool is illustrated by the development of multiple regression equations relating basal area increment to various stand parameters including foliar phosphorus levels. Mixed mode regression analysis was used, removing foliar P variables first and adding other variables stepwise. The model which best described the relationships sought was of the form: $$\log B = a_1 P + a_2 P^2 + a_3 \frac{{BA.SI}}{{Age}} + a_4 \frac{{SI}}{{BA.Age}}$$ where B = average annual basal area increment for the three-year period preceding or subsequent to foliar sampling; P = percentage phosphorus in foliage; BA = basal area standing at the time of sampling; SI = site index, defined as predominant height (predicted or actual) in feet at age 25 years; and Age = age of plantation in years at time of sampling. Using this equation, the critical level of phosphorus in slash pine (Pinus elliottii Engelm.) is set at 0.075–0.080 per cent and in loblolly pine (P. taeda L.) at 0.095–0.105 per cent. Critical level is here defined as the foliar P concentration associated with 90 per cent of maximum basal area increment. Over the range of parameters examined, the critical levels so determined are, for all practical purposes, independent of age, site index and stand density. Utilization of critical foliar nutrient levels in crop-logging requires a know-ledge of fertilizer — soil — plant interactions which can be derived in part from the fertilizer trials used to establish critical levels in the first instance.