Lc. Burns et al., DETERMINATION OF THE SIMULTANEOUS PRODUCTION AND CONSUMPTION OF SOIL NITRITE USING N-15, Soil biology & biochemistry, 27(6), 1995, pp. 839-844
Traditionally nitrite is viewed as a transient intermediate in a numbe
r of processes. Recent studies have shown that NO2- can occur in relat
ively high concentrations in soil and may be the source of concentrati
ons in river water above EU guidelines. Nitrite has the potential to b
e formed by several processes. Although there is evidence that both ox
idative and reductive processes contribute to the presence of NO2- in
soil, the relative contribution of these processes to soil NO2- flushe
s is not known. The development of sensitive techniques for determinin
g the N-15 content of soil NO2- has facilitated new studies on its tur
nover. In our study, the rates of NO2- production and consumption in s
oil were determined, using N-15-labelled NO2- and isotope dilution equ
ations. Portions of soil with a pulse of (NO2-)-N-15 were incubated in
sealed jars for 24 h. Periodically, NO2- and NO3- concentrations and
their N-15 content were determined by destructive sampling during the
experiment. The he concentration and N-15 content of the NO2- pool dec
lined rapidly during the first 6 h of the incubation, becoming more st
able thereafter. Concentrations of NO3- increased between 0 and 20 h,
as did the N-15 content of this pool. Calculated rates of NO2- product
ion and consumption indicated the speed with which NO2--N can be metab
olised within the soil. Consumption rates were 5 times greater than pr
oduction rates during the first 6 h of incubation. Generally > 50% of
NO2--N consumed was recovered in the NO3- pool, indicating that nitrif
ication was the major NO2--consuming process. It was not possible to c
alculate the relative contribution of reductive processes to NO2- cons
umption. The validity of using the isotope dilution equations is discu
ssed, and in particular the significance of the recycling of NO2--N fr
om the NO3- pool. The stabilising of NO2- production and consumption r
ates, of NO2- and NO3- N-15 contents, and of NO2--N concentrations ind
icated that recycling occurred between 20 and 24 h. The rapid metaboli
sm of NO2- in soil suggests that the NO2- in river water may not be wh
olly soil-derived. The processes responsible for the presence of NO2-
in river water need further investigation. The techniques used in this
study should be readily applied to water and sediment samples.