Kinetic formulation of oxygen consumption and denitrification processes in soil

Abstract

. 1997. Kinetic formulation of oxygen consumption and denitrification processes in soil. Can. J. Soil Sci. 77: 253-260. A kinetic expression for oxygen, nitrate, nitrite and nitrous oxide reduction in soil was developed. The formulation was based on competitive Michaelis-Menten kinetics for a steady microbial population whose respiratory activity was assumed to be constant so that the number of electrons produced per unit of time was constant. Competition among the electron acceptors was characterized by their affinity toward the electron and by their concentration. Several different values for the affinity coefficients were used to simulate the concentration of O 2 , NO 3 -, NO 2 -, N 2 O and N 2 at various times. When relative magnitudes of affinity coefficients were chosen to be 100 000, 1, 100 and 0.1, for O 2 , NO 3 -, NO 2 -and N 2 O, respectively, the temporal plot of concentration showed that the disappearance of O 2 and NO 3 -was zero order. The accumulation of NO 2 -was very small and it was rapidly reduced to N 2 O. The production rate of N 2 O was nearly zero order but the magnitude of the rate was rather small as opposed to the rate of disappearance of NO 3 -. The reduction of N 2 O to N 2 took place only after NO 3 -had almost disappeared. With these competition parameters NO 3 -was stable in the presence of O 2 . The reduction of N 2 O was also very much retarded in the presence of NO 3 -. NO 2 -was relatively unstable, even in the presence of O 2 , and it was further reduced to N 2 O. With the relative magnitude of the chosen affinity coefficients, the kinetic formulation effectively simulated the "inhibitory" effect of O 2 upon the denitrification process, and the "inhibitory" effect of NO 3 -and NO 2 -upon the reduction of N 2 O to N 2 . Nitrogen has oxidation states ranging from -3 to +5. The most reduced form, ammonium, is stable under reduced conditions and the oxidized form, nitrate, is stable under oxidized conditions. The oxidation-reduction status of the environment determines whether the oxidation of ammonium to nitrate (nitrification) or the reduction of NO 3 -to gaseous forms, such as N 2 or N 2 O (denitrification) will occur. Even though the denitrification process has been extensively investigated (Kohl et al. 1976;Betlach and Tiedje 1981;Cho 1982;Leffelaar and Wessel 1988;Dendooven et al. 1994), the mechanisms and kinetic expressions for denitrification are not fully understood. Cho and Mills (1979) proposed a competitive kinetic expression for denitrification based on steady state Michaelis-Menten kinetics. Their expression was based on a constant denitrification intensity, defined to be the sum of production rates of NO 2 -, N 2 O and N 2 from their immediate precursors. The model of Cho and Mills (1979) explains several important observations made by many workers (Blackmer and Bremner 1978;Cho and Sakdinan 1978;Gaskell et al. 1981). These include i) the apparent inhibition of N 2 O reduction by high concentrations of NO 3 -and NO 2 -, ii) the lag in the reduction of N 2 O prior ...

Effect of split application of fertilizer nitrogen on N2O emissions from potatoes

“…First, it is possible that the lower soil bulk density and lower WFPS in the hill compared with the furrow may have increased gaseous diffusion in the potato hill to allow greater O 2 supply and more rapid N 2 O escape from the site of denitrification; both processes would reduce the amount of N 2 O being reduced to N 2 during denitrification (Smith et al 2003). Second, the concentrations of NO 3 ( were greater in the potato hill, and the accumulation of NO 3 ( , which is preferentially reduced relative to N 2 O (Cho et al 1997) and inhibits nitrous oxide reductase activity (Firestone et al 1979), would result in a reduction in the conversion of N 2 O to N 2 . Third, it is possible that significant denitrification occurred in the hill below the depth of measurement.…”

“…Water is also a barrier to the diffusion of oxygen (O 2 ) to, and the escape of N 2 O from, the site of denitrification (De Klein and Van Logtestijn 1996). Soil NO 3 ( is used preferentially to N 2 O as a terminal electron acceptor (TEA) under anaerobic conditions (Firestone et al 1979;Aulakh et al 1984;Cho et al 1997). As a result, there is a strong interaction between soil aeration and NO 3 ( availability in determining N 2 O emissions (Ruser et al 2001).…”

Non‐Legume Cover Crops Can Increase Non‐Growing Season Nitrous Oxide Emissions

“…The result is increased N 2 O emissions under high NO 3 availability because microbes preferentially select NO 3 as a terminal electron acceptor under O 2 limiting conditions (Cho et al, 1997). When NO 3 is not limiting facultative anaerobic activity, the availability of the energy source (electron donor-organic C) may limit denitrification.…”

“…It is more likely that this ratio implies that the potential to emit N 2 O is a function of the supply of electron donors controlling the demand for terminal electron acceptors . A low WEOC to NO 3 ratio infers that NO 3 is more abundant relative to WEOC, thus facultative anaerobes would be more likely to preferentially use NO 3 rather than N 2 O as a terminal electron acceptor (Cho et al, 1997), thereby increasing the N 2 O to N 2 mole ratio for denitrification. At high WEOC to NO 3 ratio the electron donor source (WEOC-organic C) is more abundant than the preferred electron acceptor source (NO 3 ), thus facultative anaerobes would be more likely to use N 2 O as a terminal electron acceptor to maintain anaerobic respiration, thereby reducing the N 2 O to N 2 mole ratio of denitrification.…”

Nitrous oxide emissions from denitrification and the partitioning of gaseous losses as affected by nitrate and carbon addition and soil aeration

“…Soil NO 3 ( is a substrate for denitrification and is used preferentially to N 2 O as a TEA under anaerobic conditions (Aulakh et al 1984;Cho et al 1997). Increased soil NO 3 ( concentrations can result in increased denitrification and N 2 O emissions (Smith et al 1998).…”