Nutrition of Populus deltoides plantations during maximum production

Abstract

Maximum annual production (19 Mg ha −1) of Populus deltoides plantations in the Lower Mississippi River Valley is attained near the end of their first decade of development, which is also when the mass of the forest floor, understory and overstory canopy approach a steady state. Annual above-ground net primary production at this stage of development is partitioned into 87% overstory and 13% understory, and annual increases in the permanent tissues of the standing crop immobilize from 13 to 27% of the nutrients in flux. Above-ground nutrient pools in the standing crop (68 Mg ha −1) were about 60% of those estimated for the system at carrying capacity and, depending on the nutrient, represented 1–10% of the system's total, the remainder being in the soil (0–120 cm). The cycling of nutrients in these rapidly accumulating systems is already well developed, and is dominated by the fluxes of the biogeochemical cycle (55–97% of the requirements) and is rapid. Thus, demands on the soil nutrient pools during maximum rates of production are relatively modest, since steady-state levels of the canopy have already been attained, and such demands only replace nutrients retained in the annual increments of woody tissues.