Potential nitrification rates and associated nitrous oxide production from NANORP soils. Urrbrae, South Australia, 2010 - 2015

A series of laboratory incubations were run on soils
collected from NANORP field sites to measure potential
nitrification rates and the proportion of nitrified nitrogen
emitted as nitrous oxide. The assay assumes that aerobic
conditions are maintained, thus the nitrification rate can be
calculated as the accumulation of nitrate, and any nitrous oxide
accumulated is from nitrification only. Soils (0-10cm) were
collected and air dried or transported on ice. Soils were
stored air dry prior to sieving and use in laboratory
incubations. Prior to the assay proper, soils were moistened and
pre-incubated for at least two weeks to allow the
re-establishment of microbial processes and prevent a flush of
activity on re-wetting. At time zero, excess ammonium substrate
was added and the soil water content adjusted to defined levels.
Incubation tubes were capped with seals for the duration of the
incubation. Acetylene was injected into a subset of tubes to 10
kPa to enable the identification of denitrfying activity and
hence check that the assumption of aerobicity remains true. Gas
samples were also taken at zero, two and four days to allow the
measurement of the accumulation of nitrous oxide, carbon dioxide
and methane. Mineral nitrogen (NH4+ and NOx) were also measured
on KCl extracts of the soils. The data presented are the
nitrification rates, nitrous oxide accumulation, proportion of
nitrified nitrogen emitted as nitrous oxide, and the soil
respiration rates for all treatments in a given experiment. It
is envisaged that the data will enable the informed
parameterisation of model runs for the NANORP sites. A relative
measure of potential nitrification rates and the proportion of
nitrified nitrogen emitted as nitrous oxide will be provided.