Modelling agronomic and environmental effects of bio-based nitrogen fertilisers in Europe

Biobased waste materials, rich in nutrients and carbon, are often underutilised but could be processed into valuable biobased fertilisers (BBFs). Replacing conventional mineral fertilisers with BBFs requires understanding of their agronomic and environmental performance, which is currently lacking. This study used the Daisy model to evaluate the agronomic (dry matter and nitrogen (N) yield) and environmental (N losses to air and water) performance of eight BBFs in six European cropping systems. Mineral N fertilisation in the baseline scenarios was replaced with BBF according to three different schemes of N fertiliser replacement: Agronomic (according to 1st year fertiliser N replacement value (NFRV), typically 10-90%), Environmental (same total N as in baseline, equivalent to NFRV = 100%), and Intermediate (based on average NFRV of Agronomic and Environmental). Results indicated that under the Agronomic scheme, BBFs maintained or increased yields, but increased N losses relative to the baseline with mineral N. The Environmental scheme reduced crop yields by up to 10%, but N losses remained similar to baseline fertilisation. BBFs generally improved soil organic N or carbon stocks, indicators of soil quality. Differences in N losses and soil quality in the Agronomic scheme were mainly related to BBFs having different NFRV; a low NFRV (e.g., compost) implies higher total N inputs to maintain yields, leading to excessive N losses in the long run. This suggest that applying BBFs according to the more cautious Environmental scheme can prevent N losses from increasing above baseline levels, with only minor yield reductions (< 10%) and potential soil quality improvements. Balanced BBF recommendations should also consider content of other nutrients (phosphorus, potassium) to optimise crop production and environmental protection.