Ni-hyperaccumulators are ideal candidates for agromining on ultramafic Ni-rich soils where other technologies for metal recovery are economically unviable. However, agronomic practices can be optimised in order to fully develop agromining at a large scale. Nitrogen (N) supply is a relevant factor, since it is generally a limiting nutrient, and especially in ultramafic soils. A pot experiment using ultramafic soil was carried out to improve the performance of agromining by the hyperaccumulators Odontarrhena serpyllifolia and Bornmuellera emarginata (Brassicaceae). Six different treatments, providing different N sources, were established for each hyperaccumulator: control monoculture, monoculture with mineral N fertilisation (2*40 kg ha-1), monoculture with 2% manure addition and co-culture with 3 different nodulating leguminous species (Anthyllis vulneraria, Lotus corniculatus –both native to ultramafic areas- and the commercial cultivar Vicia sativa cv. Prontivesa). The effects of the six treatments on Ni agromining efficiency of both hyperaccumulators were assessed from different perspectives: soil physico-chemical and biological properties, plant (shoot and root) biomass and nutritive status, plant δ15N isotopic signatures, and shoot Ni concentration and Ni yield after 5 months growth. Fertilisation with manure had a strong impact on plant biomass of both hyperaccumulators and resulted in a significant increase in Ni yield (maximum values of 90 mg Ni plant-1 for B. emarginata). Increased plant biomass due to manure application also influenced other soil parameters (such as DTPA-extractable [Ni] or soil urease and arylsulphatase activities). Co-culture with leguminous species increased the shoot Ni concentration of both hyperaccumulators. However, a significant increase in Ni yield was only obtained for B. emarginata when co-cultured with A. vulneraria. Mineral fertilisation and co-culture with Vicia sativa improved root and shoot N concentration of both hyperaccumulators. These two treatments also led to increased N assimilation at the shoot level (as indicated by an increased δ15N signature between shoots and roots). Hyperaccumulators in manure treatment presented the maximum δ15N per plant. The abundance of soil microbial communities involved in N-cycling varied between treatments and species, pointing out to possible competitive effects between plants and soil microorganisms for nutrients. Bornmuellera emarginata is a promising species for Ni-agromining. Breeding for increased biomass and/or Ni concentration is needed in order to improve the use of Odontarrhena serpyllifolia for agromining in the Iberian Peninsula.