To describe the transport of the ammonium ion in different classes of aggregates of a typic Haplortox, a laboratory experiment was carried out. The treatments corresponded to a 3 x 5 factorial, being three sources of NH4+ [(NH4)2SO4, NH4Cl, and NH4NO3] and five aggregate classes (2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.105, and <0.105 mm). The experimental unit was a glass column saturated, under vacuum to which was applied a CaCl2 0.005 mole L-1 solution. After saturation, the same solution was applied until constant percolation, followed by a seven pore volume pulse of solution of respective source - 0.01 mole L-1 NH4+ (Co). Fractions of the effluent, corresponding to 0.3 pore volume (p), were collected, and the NH4+ concentrations were determined (C). C/Co relationships were calculated for every p fraction, and the experimental elution curves were traced. The highest retardation factors were calculated for the smallest aggregates, indicating a larger retention of ammonium, and the almost superimposed theoretical curves showed the predominance of the dispersive transport for ammonium. The NH4+ percolation was not affected by the studied anions in the different aggregates classes.
ammonium transport; soil aggregates; Oxysol
