Oxygen Consumption and Denitrification Kinetics in Soil

Abstract

AbstractOxygen consumption and CO2, N2O, and N2 production from a slurry of a slightly acidic soil incubated in a closed container with several different concentrations of NO‐3 were investigated using a mass spectrometer. Under unshaken conditions, the rates of O2 consumption and CO2 production changed with time. Nitrous oxide and N2 gases were produced even though there was ample O2 in the atmosphere above the stagnant water. Under these conditions the rates of O2 consumption and N2O, N2, and CO2 production were controlled by the kind and rate of supply of electron acceptors to the sites of denitrification. When well shaken, the rate of O2 consumption was constant. The CO2 production rate had two distinctive values. The rate of CO2 production when O2 was still in the system was greater than the value obtained after O2 in the system was all depleted. Nitrous oxide started to appear only when O2 was completely consumed. Under the shaken conditions, the measured rates of O2 consumption, CO2, and N2O production were independent of NO‐3 concentration; however, the average life and the maximum concentration of N2O were directly related to initial NO‐3 concentration.It is useful to define a parameter, denitrification intensity (DNI), which is proportional to the potential maximum rate of electron production for a soil with constant microbial activity under fixed temperature. Determination of the DNI must be made when the rate of electron acceptor (NO‐3 or NO‐2) supply is not limiting the reaction. Under these conditions, the inhibition of conversion of N2O to N2 results in the rate of N2O‐N production which is greater than the rate of production of the sum of N2O‐N and N2‐N without inhibition. If the rate of supply of electron acceptors (NO‐3 or NO‐2) is smaller than DNI, a parameter, gaseous nitrogen production rate (GNPR), the magnitude of which is unaffected by the inhibition of conversion of N2O to N2, characterizes the denitrification process.