MODELING POTASSIUM UPTAKE BY SLASH PINE-SEEDLINGS FROM LOW-POTASSIUM-SUPPLYING SOILS

The application of diffusion/mass-flow theory to K uptake by slash pine (Pinus elliottii Engelm. var. elliottii) seedlings from low-K-supplying soils is presented. Simulations for K uptake were evaluated by the Barber-Cushman model (BCM) and the Baldwin-Nye-Tinker model (BNTM) under greenhouse and field conditions. Potassium uptake was overpredicted by 31 to 50% in greenhouse studies; overestimates, however, are attributed to nonuniform distribution of roots along pot walls. Simulations underpredicted K uptake by 0.48 and 0.83 times that observed in seedlings grown in the field. Although ectomycorrhizal hyphae were abundant in the field, their contribution to K uptake was not incorporated. Predictions of K uptake were excellent for seedlings grown at a tree nursery when fertilizer amendments were included. The BNTM, based on simplifying assumptions, predicted K-uptake values similar to the BCM. Sensitivity analysis showed that root growth and initial K concentration in soil solution were the two most important factors affecting K uptake by slash pine. Soil processes that control K concentration were the limiting factors to K uptake on these soils. Monte Carlo procedures indicated that, for two harvests in the field, simulated estimates of uptake had CVs ranging from 34 to 64%.