Ammonia water as a biobased fertiliser: Evaluating agronomic and environmental performance for Lactuca sativa compared to synthetic fertilisers

Abstract

The European Union is actively promoting circular agriculture, aiming to reduce external inputs, close nutrient cycles, and minimise harmful emissions. This shift has spotlighted bio-based fertilisers (BBFs) as a potential substitute for energy-intensive and environmentally detrimental synthetic fertilisers. Nevertheless, research on resilience and eco-friendliness of BBFs remains limited. To address this, novel manure-derived BBF - ammonia water (AW) was examined in terms of agronomic (crop yield, nitrogen (N) fertiliser replacement value (NFRV)) and environmental (N2O, CO2, CH4, NH3) parameters in a lettuce pot cultivation. The AW had an initial alkaline pH of 11.2 (AWpHini), and another variant with pH adjusted to 5 (AWpH5) was tested for performance comparison against calcium ammonium nitrate (CAN). The agronomic efficiency was tested at three incremental N rates (30%, 60%, and 100% of crop N demand). AWpHini resulted in similar crop yield and N uptake compared to CAN for all N rates. NFRV for all N rates of AWphini exceeded 90%, however, significant reverse trend was noted for AWph5 (NFRV <90% for all rates) likely due to product's low pH affecting soil microbes. In terms of environmental performance, gaseous emissions for AWphini (52.2 CO2eq) showed significantly lower (p < 0.05) trend in comparison to CAN (120.2 CO2eq), AWph5 (114.1 CO2eq) and urea (101.3 CO2eq). The effect of acidification was observed in NH3 emissions, where AWpH5 resulted in significantly lower (p < 0.05) emissions compared to AWpHini. More research in real-world field conditions with different crops is needed to confirm ammonia water's potential as a synthetic nitrogen fertiliser replacement.