Denitrification potential and nitrate removal from solution percolating through soil above a water table were investigated using laboratory columns. The columns were packed with an Andisol subsoil (K(N)) or soil to which 10 g kg^<-1> of cellulose had been added (K+C(N)), and placed in a basin to keep the water level at 94 cm below the surface. To the upper surface of the columns, a KNO_3 solution containing 100 mg L^<-1> of NO_3-N was intermittently applied. Nitrate concentration in the effluent markedly decreased with time, both in the K(N) and K+C(N) columns, with 58 and 30% of the applied NO_3-recovered in the effluent, respectively. The NO_3-N content in the soil, determined after terminating the percolation experiments, showed a marked decrease with depth in the K+C(N) column. This was consistent with denitrification potential of the soils measured as a function of the depth above the water table. The accumulation of (N_2+N_2O)-N during anaerobic incubation was highest in soils taken from the 36-66 cm height in the K+C(N) column, where the first-order rate constant for denitrification was estimated at 5.0×10^<-6>-8.5×10^<-6>s^<-1>. In the K(N) column, the decrease of NO_3-N content with depth was less pronounced, and the rate constant for denitrification was one order of magnitude smaller. Using estimated profiles of the first-order rate constant for denitrification, the measured NO_3-N content profiles in both columns were reasonably reproduced by an approximate steady-state model for NO_3-transport. These results demonstrate that there is a good chance of nitrate removal by denitrification from solution percolating through soil above a water table, and that the nitrate concentration profile in the soil is highly dependent on the amount of easily decomposable organic matter and extent to which reducing conditions have developed in the soil.
