Bromide and nitrate movement through undisturbed soil columns

Field experiments often assume that Br(-), (14)NO(3)(-)-N, and (15)NO(3)(-)-N have similar leaching kinetics. This study tested this assumption. Twenty-four undisturbed soil columns (15-cm diameter) were collected from summit-shoulder, backslope, and footslope positions of a no-tillage field with a corn (Zea mays L.)-soybean [Glycine mar (L.) Merr.] rotation. Each of the landscape positions had a different soil series. After conditioning the columns with 4 L of 0.01 M CaCl(2) (2 pore volumes), (15)N-labeled Ca(NO(3))(2) and KBr were applied to the soil surface and leached with 4 L of 0.01 M CaCl(2). Leachate was collected, weighed, and analyzed for NO(3)(-)-N, NH(4)(+)-N, (15)N, (14)N, and Br(-). The total amount of (15)NO(3)(-)-N and (14)NO(3)(-)-N collected in 1000, 2000, and 3000 mL of leachate was similar. These data suggest that (15)N discrimination during leaching did not occur. Bromide leached faster through the columns than NO(3)(-)-N. The more rapid transport of Br(-) than NO(3)(-)-Nwas attributed to lower Br(-) (0.002 +/- 0.036 mg kg(-1)) than NO(3)(-)-N (0.17 +/- 0.03 mg kg(-1)) sorption. Results from this study suggest that (i) if Br(-) is used to estimate NO(3)(-)-N leaching loss, then NO(3)(-)-N leaching losses may be overestimated by 25%; (ii) the potential exists for landscape position to influence anion retention and movement in soil; and (iii) (15)N discrimination was not detected during the leaching process.