Estimating potentials for nitrate-N reduction and nitrogen transformations from field incubations

Fine-textured soil cores were saturated with KNO₃ solutions, withdrawn at periodic in tervals and examined for mineral N forms. Reduction of NO₃^? was correlated with time using a first-order rate function. Instantaneous initial NO₃^?-N reduction rates were determined by taking derivatives of the rate function and setting t = 0. Duplicate experiments gave maximum NO₃^?-N reduction rates of 1.0 μ N/g soil/h or ? 100 kg NO₃^?-N/ha/day. Calculated NO₃^? reduction rates increased with depth down to 30 cm. Net NO₃^?-N reduction ceased between 48 and 96 h after which net NO₃^?-N production of 0.016 to 0.29 μg N/g soil/h (～1.5 kg N/ha/day/0 to 20 cm) occurred. Net NH₄⁺-N mineralization ranged from about 0.03 to 0.05 μg N/g soil/h (3.5 to 4.0 kg N/ha/day/0 to 30 cm). Both instantaneous initial NO₃^?-N loss rates and N mineralization rates are similar to results of laboratory studies elsewhere on similar soil types. This procedure for estimating N-transformations may be useful where other techniques are either not adequate or not feasible for field use.