NITRATE SORPTION IN THE PROFILE OF AN ACID SOIL

Sorption of NO3- 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 NO3- in the 90-120 cm-layer at water and NO3-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 NO3- and chloride were found to be independent, suggesting that anion exchange sites were far from saturated.