THE INFLUENCE OF INCREASED NH4+ DEPOSITION RATES ON ALUMINUM CHEMISTRY IN THE PERCOLATE OF ACID SOILS

The influence of different NH4+ loads on aluminiums speciation in percolating water was studied on acid luvisols with similar soil-pH values but with different soil adsorption surface characteristics. All of the applied NH4+ was nitrified and therefore led to proton production. Thus, Al displacement in the percolate was increased. The extent of this enhanced translocation was found to be chiefly a function of the amount of exchangeable base cations which buffered the protons produced by nitrification. The proportion of the different Al species in the percolate was altered at large NH4+ loads. Very large Al3+ concentrations eliminated Al species bound to dissolved organic matter and particles, presumably because of flocculation and precipitation of organic ligands. Furthermore, increased NO3- and Al3+ concentrations enhanced the desorption of F- giving rise to an additional increase in Al displacement by the formation of Al fluoro complexes in the aqueous phase.