CHAMBER MEASUREMENT OF SOIL-ATMOSPHERE GAS-EXCHANGE - LINEAR VS DIFFUSION-BASED FLUX MODELS

We compared linear regression with a diffusion-based model for N2O flux estimation using non-steady-state chamber gas concentrations from a long-term study of N cycling in a managed grass pasture on sandy soil in southern Texas, Of 2224 chamber deployments, 449 met criteria established for using the diffusion-based model, which yielded flux estimates that averaged 54% larger than linear regression (n = 3). Although they represented only about 20% of all chamber deployments, this group included most of the data with greatest influence on the magnitude and dynamics of total N2O exchange at our site; e.g., of the 263 fluxes >10 g N ha(-1) d(-1), 199 (or 73%) were included, Apparently, application of a linear model to nonlinear chamber concentration data represents a potentially serious source of measurement bias that may influence not only summary statistics for the experiment, but also larger scale budgets based partially or wholly on those data.