Nutrient supply changes within a growing season in two deciduous forest soils

Little information is available on how the indices of nutrient availability used in mechanistic nutrient uptake models might be influenced by the temp erature at which the equilibrium soil solution (C-1) is extracted or how th is parameter, and the solid-phase nutrient concentration (C-s) might be alt ered by the progression of the growing season. Objectives of this study wer e to determine: (i) if the laboratory extraction temperature would influenc e C-1 estimates, and (ii) the degree of change in C-1 and C-s during the gr owing season. Soil samples were collected from two forest sites in eastern Tennessee In April, July, and October, Samples were returned to the laborat ory and equilibrium soil solution concentrations of NO3-N, NH4-N, P, K, Ca, and Mg determined at the average soil temperature (11-18 degrees C) or at laboratory temperature (24 degrees C), Solid-phase (C-s) concentrations wer e also determined and both values used to calculate the buffer power (b) an d the effective diffusion coefficient (D-e), Extraction temperature did not alter C-1 values, All solution nutrient concentrations except P declined b y 16 to 99% after the July sample. Increases in P in the A horizon at one s ite were as high as 100%. Solid-phase nutrient concentrations exhibited dec lines ranging from 6 to 91% while solid-phase P concentrations increased by up to 40%, Disproportionate changes in the C-1 and C-s values lead to chan ges in the calculated b and D-e estimates. Results indicate that efforts di rected at establishing soil supply parameters needed for mechanistic nutrie nt uptake models should take into consideration changes that occur in solut ion and solid-phase nutrient concentrations during the growing season.