Fig. 8 Denitrification rate and NO-3 concentrations at the 5- and 20-cm depths of the soil solution sampled by suction plates. Denitrifying activity was measured with three pairs of cores during the NH+4 addition and with four pairs of cores during the NO-3 addition. NO-3 concentrations are the mean of two suction plates, installed within 50 cm of the microcups