Management practices of Miscanthus x giganteus strongly influence soil properties and N2O emissions over the long term
Résumé
Cropping practices of Miscanthus × giganteus, a promising energy crop, can influence C and N cycles and therefore potentially affect N2O emissions. They may vary in harvesting date, either early (EH) or late harvest (LH), and the fertiliser form (NH4 or NO3). 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, N2O emissions and the contribution of nitrification and denitrification. Daily N2O fluxes and soil parameters were measured during the 4-month period following fertilisation in 2014 and 2015. Mean cumulative N2O emissions were markedly higher in LH than EH (4.21 vs. 0.89 kg N2O–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 N2O emissions. The large decrease in pH observed after NH4 fertilisation stimulated N2O emissions probably through less-efficient reduction of N2O to N2 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 N2O 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.