Nutrient Supply and Fertilization Efficiency in Midrotation Loblolly Pine Plantations: A Modeling Analysis

We simulated the 10 yr macronutrient budgets for 14 installations in a regionwide midrotation loblolly pine (Pinus taeda L.) fertilization study using NUTREM, a simplified model of carbon and nutrient uptake and distribution. Each installation includes 2–4 replications of N and P addition in a two-way factorial design. By approximating the constraints on nutrient use as elements in a linear programming problem, and estimating the parameters of the problem using least squares, we were able to identify baseline soil supply rates and fertilization efficiencies for N and P for each installation. Estimated N supply ranged from 47 kg ha-1 yr-1 to 103 kg ha-1 yr-1, while P supply ranged from 5.5 to 12.4 kg ha-1 yr-1. Fertilization efficiencies were extremely variable, ranging from 23% to 100% for N and 0% to 78% for P. A lower bound to the baseline supply rate was identified for K, Ca, and Mg for each site. While only three sites were P-limited, P limitation was imminent on all sites with operational doses of applied N. While the accuracy of NUTREM is limited by the availability of basic process-level data, the method suggests possibilities for predicting growth response to nutrient amendments. FOR. Sci. 47(1):96–102.