Integrating winter legume cover crops in temperate rice cropping systems for enhancing carbon and nitrogen inputs without increasing GHG emissions

Transitioning to low-input cropping systems while enhancing soil fertility and limiting greenhouse gas (GHG) emissions is a major challenge for temperate rice cultivation. In northern Italy, cultivating a winter leguminous cover crop (CC) in conventional monocropped rice systems may represent an important source of organic matter (OM) to sustain soil fertility and nitrogen (N) for crop nutrition. However, incorporating fresh green manure before flooding may also stimulate methane (CH4) production by increasing the availability of labile OM under anaerobic conditions. This study evaluated the agronomic and environmental implications of introducing Vicia villosa Roth as a winter CC in a rice-based system managed under dry seeding followed by continuous flooding. Plots with CC were compared to a winter fallow over two consecutive growing seasons, during which biomass inputs, porewater chemical composition, GHG fluxes, and soil organic matter (SOM) composition were evaluated. Hairy vetch established successfully in both years and provided inputs of 1.91 ± 0.32 and 2.72 ± 0.19 t C ha-1 and 180 ± 30 and 240 ± 30 kg N ha-1. Cumulative methane emissions over the entire rice growing cycle, as well as the global warming potential, showed no statistically significant differences between the treatments. Overall, these results suggest that integrating hairy vetch as a winter cover crop preceding dry-seeded temperate rice can substantially increase organic matter and N inputs without an evident trade-off in seasonal CH4 emissions, thereby supporting the development of low-input and more environmentally sustainable rice paddy management strategies.