Retarded leaching of nitrate in acid soils from the tropics: measurement of the effective anion exchange capacity

Abstract

SUMMARY Delay in the leaching of nitrate was measured in laboratory columns of repacked soils (Oxisols, Alfisols, Ultisols and Inceptisols) from South America, Africa and South‐East Asia. Between one and five pore volumes were required for the frontal displacement of chloride by nitrate (2 mM adjusted to the natural pH of the soil). The delay was in good agreement with that calculated from charge (0 to 1.7 cmol positive charge kg −1 ). Measurement of charge by batch equilibration with 0.5 M and then 2 mM NH 4 CI at the pH of the soil overestimated the effective charge, probably due to removal of sulphate in the washings. A leaching method using only 2 mM NH 4 CI gave a better estimate.