Agronomic and environmental performance of animal manure-derived ammonium salts vs synthetic mineral fertilisers: 4-year field trial evidence

The European Union (EU) increasing focus on sustainable practices, especially in agriculture, highlights the critical importance of addressing concerns related to the geographical polarity of nutrients and the limited availability of natural reserves. This growing awareness is fueling the adoption of eco-friendly bio-based fertilisers (BBFs) over their mineral counterparts. This study addresses this knowledge gap by subjecting two BBFs, ammonium sulphate (AS) and ammonium nitrate (AN), to a comprehensive 4-year field trial involving crop rotation with maize, spinach, and potatoes at incremental application rates of 40 %, 70 % and 100 % crop total nitrogen (N) demand. The study also evaluates the environmental impacts of these BBFs by comparing gaseous emissions and nitrate leaching risks against their mineral counterparts. Despite challenges arising from the variability in weather conditions during the 4 years of the trial, the selected BBFs demonstrated comparable performance to synthetic ammonium nitrate. The comparative yield range ratio (Yield BBF : Yield mineral fertiliser ) ranged from 0.86 to 1.09 for AS and from 0.49 to 1.02 for AN throughout the 4-year field trial duration at 100 % N rate. Moreover, laboratory-based experiments showed significantly lower gaseous emissions for AS (10.39 CO₂-eq) and AN (2.81 CO₂-eq) than for their mineral counterpart (15.25 CO₂-eq), likely reflecting slower mineralisation, reduced N₂O emission peaks, and soil pH dynamics relative to the calcium ammonium nitrate reference. Additionally, residual nitrate during winter period from field in the soil remained similar in the case of BBFs and mineral counterparts at all dosages for all 4 years. This indicates that crop uptake and seasonal variability outweighed differences in fertiliser source. These findings emphasize the potential of BBFs to perform at par with mineral fertilisers while offering environmental benefits, making them well suited as a future alternative in circular agriculture. • BBFs (AS, AN) gave crop yields comparable to mineral fertilisers in 4 years. • Gaseous emissions were lower for BBFs than for calcium ammonium nitrate. • Residual winter soil nitrate was similar for BBFs and mineral fertilisers. • BBFs maintained performance despite weather variability across trial years. • BBFs can sustain yields while reducing emissions in circular agriculture.