A new conceptual framework explaining spatial variation in soil nitrous oxide emissions

Abstract

Soil emissions of nitrous oxide (N2O), a potent greenhouse gas, contribute substantially to global warming from agriculture. Spatial variation in N2O emissions within agricultural fields leads to high uncertainty in the benefits of climate-smart agricultural practices. Here, we present a new conceptual framework explaining spatial variation in soil N2O emissions developed from high spatial resolution automated measurements of soil N2O emissions together with measurements of gross N2O fluxes and soil physicochemical properties in two separately managed maize fields in central Illinois, USA. We found that sub-field locations with consistently low N2O emissions had distinct biogeochemical properties compared to locations where high emissions occurred episodically, leading to spatial variation in which factors control N2O production rates. In the consistent N2O cold spots, soil nitrate (NO3-) and dissolved organic carbon (DOC) constrained N2O production irrespective of changes in soil moisture. In contrast, in the episodic N2O hot spots which had higher soil NO3- and DOC availability, N2O production was stimulated by increases in soil moisture. These findings form the cannon model which conceptualizes how sub-field scale variation in soil NO3- and DOC determines where increases in soil moisture can trigger high soil N2O emissions within agricultural fields.