Acknowledgements The authors would like to thank the Spanish National R+D+i Plan (AGL2012-37815-C05-01, AGL2012-37815-C05-04) and very specifically the workshop held in December 2016 in Butrón (Bizkaia) to synthesize the most promising measures to reduce N2O emissions from Spanish agricultural soils. BC3 is sponsored by the Basque Government. M. L. Cayuela thanks Fundación Seneca for financing the project 19281/PI/14. This paper has been produced within the context of the REMEDIA network: http://redremedia.wordpress.com/.Peer reviewedPostprintPostprin

Nitrification inhibitors (NIs) such as dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) provide an opportunity to reduce losses of reactive nitrogen (Nr) from agricultural ecosystems. To understand the fate and efficacy of these two inhibitors, laboratory-scale experiments were conducted with ¹⁴C-labelled DCD and DMPP to determine the relative rates of mineralization, recovery in soil extracts and sorption in two agricultural soils with contrasting pH and organic matter content. Concurrently, the net production of soil ammonium and nitrate in soil were determined. Two months after NI addition to soil, significantly greater mineralization of ¹⁴C-DMPP (15.3%) was observed, relative to that of ¹⁴C-DCD (10.7%), and the mineralization of both NIs increased with temperature, regardless of NI and soil type. However, the mineralization of NIs did not appear to have a major influence on their inhibitory effect (as shown by the low mineralization rates and the divergent average half-lives for mineralization and nitrification, which were 454 and 37days, respectively). The nitrification inhibition efficacy of DMPP was more dependent on soil type than that of DCD, although the efficacy of both inhibitors was lower in the more alkaline, low-organic matter soil. Although a greater proportion of DMPP becomes unavailable, possibly due to physico-chemical sorption to soil or microbial immobilization, our results demonstrate the potential of DMPP to achieve higher inhibition rates than DCD in grassland soils. Greater consideration of the interactions between NI type, soil and temperature is required to provide robust and cost-effective advice to farmers on NI use.

Agronomical and environmental benefits are associated with replacing winter fallow by cover crops (CCs). Yet, the effect of this practice on nitrous oxide (N₂O) emissions remains poorly understood. In this context, a field experiment was carried out under Mediterranean conditions to evaluate the effect of replacing the traditional winter fallow (F) by vetch (Vicia sativa L.; V) or barley (Hordeum vulgare L.; B) on greenhouse gas (GHG) emissions during the intercrop and the maize (Zea mays L.) cropping period. The maize was fertilized following integrated soil fertility management (ISFM) criteria. Maize nitrogen (N) uptake, soil mineral N concentrations, soil temperature and moisture, dissolved organic carbon (DOC) and GHG fluxes were measured during the experiment. Our management (adjusted N synthetic rates due to ISFM) and pedo-climatic conditions resulted in low cumulative N₂O emissions (0.57 to 0.75 kg N₂O-N ha⁻¹ yr⁻¹), yield-scaled N₂O emissions (3–6 g N₂O-N kg aboveground N uptake⁻¹) and N surplus (31 to 56 kg N ha⁻¹) for all treatments. Although CCs increased N₂O emissions during the intercrop period compared to F (1.6 and 2.6 times in B and V, respectively), the ISFM resulted in similar cumulative emissions for the CCs and F at the end of the maize cropping period. The higher C : N ratio of the B residue led to a greater proportion of N₂O losses from the synthetic fertilizer in these plots when compared to V. No significant differences were observed in CH₄ and CO₂ fluxes at the end of the experiment. This study shows that the use of both legume and nonlegume CCs combined with ISFM could provide, in addition to the advantages reported in previous studies, an opportunity to maximize agronomic efficiency (lowering synthetic N requirements for the subsequent cash crop) without increasing cumulative or yield-scaled N₂O losses.