The anaerobic soil volume as a controlling factor of denitrification: a review

Denitrification is an important component of the nitrogen cycle in soil, returning reactive nitrogen to the atmosphere.
Denitrification activity is often concentrated spatially in anoxic microsites and temporally in ephemeral events, which
presents a challenge for modelling. The anaerobic fraction of soil volume can be a useful predictor of denitrification in
soils. Here, we provide a review of this soil characteristic, its controlling factors, its estimation from basic soil properties
and its implementation in current denitrification models. The concept of the anaerobic soil volume and its relationship
to denitrification activity has undergone several paradigm shifts that came along with the advent of new oxygen and
microstructure mapping techniques. The current understanding is that hotspots of denitrification activity are partially
decoupled from air distances in the wet soil matrix and are mainly associated with particulate organic matter (POM) in the
form of fresh plant residues or manure. POM fragments harbor large amounts of labile carbon that promote local oxygen
consumption and, as a result, these microsites differ in their aeration status from the surrounding soil matrix. ... mehrCurrent
denitrification models relate the anaerobic soil volume fraction to bulk oxygen concentration in various ways but make
little use of microstructure information, such as the distance between POM and air-filled pores. Based on meta-analyses,
we derive new empirical relationships to estimate the conditions for the formation of anoxia at the microscale from basic
soil properties and we outline how these empirical relationships could be used in the future to improve prediction accuracy of denitrification models at the soil profile scale.