Management Practices of Miscanthus × giganteus Strongly Influence Soil Properties and N 2 O Emissions Over the Long Term

Cropping practices of Miscanthus × giganteus , a promising energy crop, can influence C and N cycles and therefore potentially affect N 2 O emissions. They may vary in harvesting date, either early (EH) or late harvest (LH), and the fertiliser form (NH 4 or NO 3 ). In this study, we combined a long-term field experiment and simulations with the STICS model to investigate the effect of these practices on soil parameters, N 2 O emissions and the contribution of nitrification and denitrification. Daily N 2 O fluxes and soil parameters were measured during the 4-month period following fertilisation in 2014 and 2015. Mean cumulative N 2 O emissions were markedly higher in LH than EH (4.21 vs. 0.89 kg N 2 O–N ha −1 year −1 ) but did not differ significantly between fertiliser forms or years. The difference was mainly attributed to the higher soil water-filled pore space (WFPS) observed in LH (80 vs. 56 % in EH) which resulted itself from the leaf mulch present in LH and not in EH. WFPS explained 67 % of the variance of N 2 O emissions. The large decrease in pH observed after NH 4 fertilisation stimulated N 2 O emissions probably through less-efficient reduction of N 2 O to N 2 as simulated by STICS. Model outputs suggest a large contribution of nitrification in EH and a dominant contribution of denitrification in LH. Our study highlights the crucial impact of management practises on N 2 O emissions in Miscanthus crops through changes in physico-chemical parameters and soil processes on the short and long term and brings knowledge required to maximise the benefits of bioenergy crops.