## 3 Results and Discussion
### Emissions from the Bio-Based Fertilisers  
The N2O emissions of all three BBFs were measured over 18 days and compared with mineral fertilisers (i.e., CAN and urea). In the mesocosm, the principle of production of N2O follows simultaneous nitrification (oxidation of NH4+ to NO3- via NO2-) and denitrification (reduction of NO3- to N2O and N2) [32]. Following this process, the mineral fertilisers showed highest emission of N2O (0.11 \(\pm\) 0.02% for urea and 0.11 \(\pm\) 0.01% for CAN) (Figure 4A). This is because of the rapid hydrolysis of products after application, resulting in increased NH4 availability. This further led to nitrification followed by denitrification, resulting in N2O production. This could also be observed in the case of AS (0.03 \(\pm\) 0.008% of AS N applied) and LFD (0.02 \(\pm\) 0.005% of LFD N applied), where the initial concentration of mineral N was \(\sim\)100% and \(\sim\)80% of total N (Table 5). Additionally, a similar result to CAN is observed for KC, where emission of 0.05 \(\pm\) 0.03% of KC N applied could be observed. These results for KC are expected due to the combination of two factors--a moderate NH4 percentage at the initial application (-33%), and a high TOC content in the fertiliser (Table 1). As the OC serves as an energy source for denitrification, the overall oxygen content in the soil decreases, promoting denitrification of NH4 in BBFs [33]. This shows a strong correlation between the N2O emissions and initial ammonium (NH4+) content which is also supported by different studies [20; 28; 29; 30]. Therefore, highest N2O emissions were observed in the soils that were treated with mineral fertiliser, which is also confirmed by [34]. The CO2 flux developed in the soil is mainly produced by the respiration of soil microorganisms and dead plant roots. The CO2 emissions from the mesococosm are directly dependent on the initial OC content available in the BBFs and mineral fertilisers. The KC and LFD had the highest amount of OC resulting respectively in emissions of 8.97 \(\pm\) 3% and 25.9 \(\pm\) 5% of total C added from the product. Urea also consisted of 20% carbon and showed rapid mineralisation due to hydrolysis, hence resulting in around 60% of CO2  
Figure 4: Cumulative emissions of nitrous oxide (mg N2O-N per m2 of soil) (**A**), carbon dioxide (g CO2-C per m2 of soil) (**B**), and methane (mg CH4-C per m2 of soil) (**C**) emissions measured during incubation of digestate-derived organic fertilisers. Legend: AS—ammonium sulphate, LFD—liquid fraction of digestate, KC—potassium concentrate, and CAN—calcium ammonium nitrate. emissions within the first five days of the experiment. In general, organic fertilisers produce considerably higher outcomes because they enhance the fraction of OC in the soil, which is more readily available for microorganisms in respiration [35]. Therefore, the released C from BBFs in soils is seen as biogenic C and is considered to be C-neutral as it does not contribute to the net CO\({}_{2}\) increase. The results for AS and CAN are not shown in Figure 4B as a negligible amount of OC is present in both cases to cause any CO\({}_{2}\) emissions. Any type of CO\({}_{2}\) emissions seen in these products is due to the positive priming effect of the already available carbon present in the soil. Across the study, the CH\({}_{4}\) emissions were significantly low due to the presence of aerobic conditions during the course of incubations (Figure 4C). Moreover, the application of manure-derived products on soil proved to enhance soil aeration, hence reducing CH\({}_{4}\) emissions [35]. The phenomenon of methanogenesis and methanotrophy derives the net soil CH\({}_{4}\) flux [36]. In the case of all BBFs as well as mineral fertilisers (CAN and urea) the CH\({}_{4}\) uptake is higher than CH\({}_{4}\) production, hence resulting in negative methane emissions from the soil. The GHG emission factors (EFs) were computed for CH\({}_{4}\), CO\({}_{2}\), and N\({}_{2}\)O (Table 5).