Bromide Leaching on a Piedmont Toposequence

Solute leaching on the field-scale is a poorly understood, complex process affected by local soil variation and landscape position. We hypothesized that Br ion leaching is a function of landscape position in a well-structured, clayey soil on a Piedmont toposequence that had been in pasture for the previous 30 yr, Dry KBr, mixed with sand at a ratio of 12 g sand to 1 g KBr, was surface-applied at a rate of 314 kg Br ha(-1) on 24 May 1994 along two transects and allowed to move into the-soil under natural rainfall conditions. Soil cores 0.90- and 2.00-m-long were taken 13 June and 20 Dec. 1994, respectively (corresponding to 20 and 210 d after Pr application and 15 and 63 cm rain, respectively). The cores were subdivided into increments 10 or 15 cm, oven dried, and analyzed for Pr, Centers of Br mass at both sampling times were significantly deeper in the footslope position (31 and 82 cm for June and December, respectively) compared with the shoulder and linear slope positions combined (25 and 70 cm for June and December, respectively), which was possibly due to lower clay contents (44 vs. 50% clay) and lower water retention (37 vs. 43 cm in the:top meter in December) for the footslope vs. the linear and shoulder slopes combined, respectively. Predicted leaching depths were calculated from measured soil water content profiles and were positively correlated with observed depths to the center of Pr mass for the Dec. 20 sampling (r(2) = 0.35, P < 0.007). Anion leaching may be partially controlled by landscape position, and soils susceptible to initial rapid leaching may not necessarily be susceptible to sustained rapid leaching throughout the year.