EFFECT OF REDOX POTENTIAL ON UREA HYDROLYSIS AND NITRIFICATION IN SOIL SUSPENSIONS

Abstract

We conducted laboratory experiments to determine urea-N transformations in four rice soils maintained under oxidized and reduced conditions. Urea hydrolysis rates differed significantly between oxidized and reduced soil suspensions. Urease activity showed considerable variation with flooding, and for three soil suspensions hydrolysis rates were faster under aerobic conditions. Urea hydrolysis followed first-order kinetics, and rate constants in oxidized acid soil suspensions ranged from 0.054 to 0.094 h−1(t1/2= 7.4 to 13.8 h) and under reducing conditions from 0.028 to 0.062 h−1(t1/2= 11.2 to 24.8 h) after urea application of 50 μg N g−1soil. For the calcareous soil, disappearance of urea was faster under a reducing environment (0.403 h−1), compared with the oxidized rate (0.369 h−1). Ammonium production under reducing conditions ranged from 0.50 to 4.74 μg NH4+–N g−1h−1, and nitrification in oxidized soil suspensions showed a significant linear relationship over initial sampling periods, and rates ranged from 0.16 to 0.72 μg NO3−–N g−1h−1. © 1989 The Williams & Wilkins.