Nitrate sorption in the profile of an acid soil

Sorption of $NO_3^ - $ by different horizons of a highly weathered, acid tropical soil was measured in laboratory batch experiments. Sorption was found to increase with depth, ranging from small amounts in the 0-15 cm layer to amounts that would be roughly equivalent to 25 to 50% of the $NO_3^ - $ in the 90-120 cm layer at water and $NO_3^ - $ contents commonly found under field conditions. Calculations, based on sorption isotherms, demonstrated how sorption may be important for managing N in a tropical acid soil. Sorption of Cl⁻ was also found in the range of 0.1 and 2.0 mol m⁻³. In this range of concentrations sorption of $NO_3^ - $ and chloride were found to be independent, suggesting that anion exchange sites were far from saturated.