Evaluating the performance of biobased, recovered nitrogen fertilizers in European cropping systems using modelling

Biobased fertilizers (BBFs) are gaining attention for their potential to advance a circular economy. This study used the Daisy model to evaluate the performance of three BBFs—ammonium sulphate (AS), digestate (DIG), and liquid fraction of digestate (LFDIG)—compared to baseline fertilization (mineral and manure) across ten European cropping systems. BBFs replaced baseline fertilization under three scenarios: (i) full replacement with equivalent total N input, (ii) full replacement with higher total N input due to BBFs' lower (<100%) fertilizer replacement values (FRVs, relative substitution rate of BBF to synthetic fertilizer), and (iii) partial replacement (only manure-N) with equivalent total N input. Results indicated that under both partial and full replacement scenarios with equivalent total N input, AS, DIG, and LFDIG had minimal impacts (<5%) on crop N yield, nitrogen use efficiency (NUE), and total N losses (gaseous and leaching) compared to the baseline. The soil organic N (SON) stocks either decreased or changed more slowly with AS and LFDIG. In scenario ii (higher total N input), BBFs led to increased N yield (2–18%) and N losses (avg. 76%), and decreased NUE (2–25%) relative to the baseline. DIG was the most effective at improving SON stocks (average increase 4.9 ​kg ​N ha⁻¹y⁻¹) and reducing N losses, followed by LFDIG and AS. The impact on N leaching varied, with higher leaching observed in annual cereal-based compared to semi-perennial grass-based systems. Implications are that BBFs should be applied assuming a high FRV (∼100%), ensuring equivalent total N input when replacing baseline fertilization to prevent increasing N losses.