Oxidation of Ammonium to Nitrate in a Soil Column

Abstract

A mathematical model based on Michaelis‐Menten kinetics for oxidation of ammonium to nitrate during downward flow in a column of soil mixed with sand has been tested. First the column was perfused with nitrite to stimulate the growth of nitrite oxidizing microorganisms in order to decrease the concentration of nitrite at any time in the column during subsequent perfusion with ammonium. The nitrite oxidizers multiplied in a quasilogistic fashion to nearly maximal numbers, exceeding ammonium oxidizers by at least a factor of 102. After a population density of 103/cm3 was reached for NO2‐ oxidizers, the column was perfused with ammonium solution; in a steady state the ammonium concentration decreased with depth (proportional to time of flow) in accord with Michaelis‐Menten kinetics. The rate constants for oxidation of NH4+ were proportional to the numbers of ammonium oxidizing microorganisms extant at any given time of observation; these numbers increased exponentially at first but leveled off after about 3 weeks of continuous perfusion of the column.As expected, the decline of ammonium concentration with depth during solution flow just equalled the appearance of nitrate with very low concentrations of nitrite in the steady state. From the data the normalized rate constant is 4.5 × 10‐3 ppm cm3/hour per microbe at room temperature, about five times greater than the corresponding figure for nitrite oxidation.

Nitrogen surface runoff losses from a Chinese cabbage field under different nitrogen treatments in the Taihu Lake Basin, China

“…Zhang et al (2009) 66-17.69%, 6.41-11.72%, and 7.42-13.35% in 2010, 2011, and 2012, respectively (Table 6), significantly lower than the percentages represented by NO 3 − -N. These results were observed primarily because NH 4 + -N is easily adsorbed by both soil particles and soil organic matter (Ardakani et al, 1974;Rosenfeld, 1979). Under aerobic conditions, NH 4 + -N can be quickly converted into NO 3 − -N through nitrification and can also be lost through ammonia volatilization (Koper et al, 2010;Salazar et al, 2012).…”

Consecutive Steady State Reactions of Urea, Ammonium and Nitrite Nitrogen in Soil

“…Figure 2 shows that the models Fig. 2 (Ardakani et al 1973(Ardakani et al , 1974 Tabatabai (1973) Tabatabai (1973) Fig. 2 with Fig.…”

“…As before (Ardakani et al 1913(Ardakani et al , 1974, experimental conditions were so chosen as to minimize the effect of dispersion and adsorption.…”

Nitrification Studies at Non-limiting Substrate Concentrations

“…It may also explain our failure to observe the overshoots in nitrite and nitrate concentrations following decrease in flow rate that were observed by these workers. Ardakani et al (1974) found negligible amounts of nitrite but this was probably due to previous enrichment of the soil with nitrite allowing development of a maximum Nitrobacter population before addition of ammonium. Very low nitrite concentrations are found in soils which are actively nitrifying.…”

“…Again there was no evidence of a biomass gradient and numbers in the column were two to three orders of magnitude lower than for Nitrobacter. Ardakani, Rehbock & McLaren (1974) determined numbers of Nitrosomonas in a sand-soil column supplied with ammonium and found a reduction in numbers near the base of the column where ammonium had been completely utilized. Such a reduction would not be expected here because conversion was never complete within the column.…”