Simulation of nitrous oxide peak emissions from a Dutch peat soil with SWAP-ANIMO

Nitrous oxide (N2O) is a very strong greenhouse gas, with agricultural soils as its main anthropogenic source. Various management practices, like fertilization or tillage, can give rise to pulses of N2O emissions. In spite of their short duration, in the order of a couple of days to weeks, these pulses can constitute a major part of total annual N2O emission. Understanding, predicting and ultimately mitigating these pulses poses a considerable challenge. In this study the model combination SWAP-ANIMO is used to assess the sources of N2O peak emissions in a Dutch peat land. The results show that the simulation of highly dynamic N2O fluxes is possible, but requires accurate modelling of the hydrology, the carbon cycle and the nitrogen cycle. Failure in the simulation of peak emissions can be traced back to failures in the simulation of soil moisture content. In peat lands, including macropores is expected to improve the simulation of soil moisture, especially after dry periods. Peak emissions from peat land are the result of coupled nitrification-denitrification. Nitrification produces continuously nitrate, which is the substrate for peak emission of N2O produced by denitrification. Only after ammonium fertilization nitrification contributes directly to the peak emissions. The larger peaks occur just after soil saturation, when the groundwater level is decreasing. N2O production then takes place just above the groundwater level.