Transient N2O accumulation and emission caused by O2 depletion in soil after liquid manure injection

Abstract

Emission of nitrous oxide (N2O) from soils is the net result of N2O-producing and consuming processes within the soil, and studying the regulation of these processes in the real soil environment is essential to the understanding of the factors governing N2O emission. In this study, microscale distributions of O2 and N2O in the soil were investigated to describe how N2O production within, and emission from, soils are regulated by anoxic volumes created by injection of liquid manure. An application device simulating field injection methodology was developed and liquid pig manure was injected at a depth of 5 cm into boxes containing soil. Microsensors with <0.12 mm tip diameter were used to measure high-resolution vertical N2O and O2 concentration profiles though the centre of the horizontally positioned soil-manure core and up to 4 cm laterally away from the centre. Both microsensor measurements and N2O emission rate determinations, with a closed chamber, were performed daily. Injected manure filled the original air-filled pore space of a 6-cm-wide cylindrical core and created anoxia. Nitrous oxide was detected in the anoxic part of the core, indicating N2O production by denitrification in the entire anoxic volume. Although anoxia was present in the core during all 3 days of the experiment, a peak rate of net N2O production was detected after 1 day, with a maximum N2O accumulation of 500–700 Pa in the core. Comparison of the cumulated N2O net production and emission revealed a delay of N2O emission, as N2O was trapped inside the saturated core.