Abstract
Nitrate (20 mg N03‐ N l−1) was leached through 180 cm columns of oxisol subsoil until the leachate attained the initial nitrate concentration. Leaching was continued with water until no nitrate was detectable in the leachate. The Δ15N for the first aliquot of leachate containing nitrate was 2.2 units lower than that of the added solution indicating that 15Nwas preferentially adsorbed to 14N. The breakthrough curve for nitrate indicated that nitrate adsorption decreased after six pore volumes. The implications for modelling nitrate leaching are discussed.