Spatial Scale of Bromide Leaching into Initially Wet and Dry Soil.

Solute concentrations vary significantly in space at the field scale as a function of many soil state variables. This study was conducted to characterize the spatial variability of solute concentrations during leaching and to identify their spatial correlation length. The effect of 40 mm rainfall (22mm/hr) on the leaching depth and concentration of Bromide applied as 40 g KBr/m² was studied in a Maury Silt Loam soil. Two different auger types were used to evaluate the influence of the soil volume sampled within an initially wet and an initially dry soil in an 18.5-m-long plot. Anion concentrations measured by colorimetric standards for Bromide were found spatially correlated below 10 and down to 40 cm depth. Auger size did not have an effect on Bromide mass recovery measured with an anion chromatograph whereas the initially dry soil showed low recovery (20 %). Spatial sampling distances of 0.25 m were adequate to characterize the spatial distribution of leaching depth of Bromide since observations were auto-correlated over 0.75 m for each 10-cm increment between 10 and 40 cm depth. Solute concentrations in subsequent horizontal depth compartments were crosscorrelated over two lag distances. Solute concentrations below 50 cm were < 2 ppm in the dry soil, and the center of mass was found in the 0-10 cm layer whereas simulations with HYDRUS-1D showed it at 13.9 cm. For the initially wet soil, the center of mass was found at 10-20 cm in good agreement with the simulation model. Measured anion concentrations at the 40-50 cm layer were > 10 ppm suggesting deeper leaching than indicated by the simulation model.