Application technique affects the potential of mineral concentrates from livestock manure to replace inorganic nitrogen fertilizer

It has been suggested that mineral concentrates (MCs) produced from livestock manure might partly replace inorganic N fertilizers, thereby further closing the nitrogen (N) cycle. Here, we quantified nitrogen use efficiency (NUE) and N loss pathways associated with MCs, compared with inorganic fertilizer and manure. In a 26-day greenhouse experiment with ryegrass (Lolium perenne L.), the effects of application technique (surface application vs. injection) and N source (control, two types of MC, three inorganic fertilizers or pig slurry) were compared. We measured yield, ammonia volatilization, nitrous oxide emission and denitrification. With surface application, NUE for MCs (38% for MC1 and 22% for MC2) was significantly lower than for calcium ammonium nitrate (CAN; 61%) and comparable with PS (25%). This was most likely due to higher ammonia emissions. After injection, the NUE of MC was comparable with that of CAN. Denitrification and N2O emission from surface-applied MC were comparable with those from surface-applied PS. After injection, MC behaved similarly to inorganic fertilizers. We conclude that MCs should be injected to maximize NUE and to fulfil their potential as inorganic fertilizer replacement. Significant NUE differences between MCs suggest the possibility for further optimization of the MC production process.