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

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.