## 2 Materials and Methods
### GHG Emissions and Soil Analysis  
The production of GHGs (CO\({}_{2}\), N\({}_{2}\)O, CH\({}_{4}\)) was measured after 1, 2, 4, 6, 8, 11, 15, and 22 days of incubation using a portable DX4040 Fourier Transformed Infrared (IR) Spectroscopy (FTIR)-Gas Analyzer (Gasmet Technology Oy, Helsinki, Finland). The detected signal is digitized, and Fourier transformed resulting in an IR spectrum of the sample gas. Background calibration with pure N (99.999%) was performed before each measurement. The instrument is equipped with Teflon tubes with quick-connect fittings and an on-board sample pump, which has a neoprene diaphragm membrane, maximum pressure is 1.0 bar, and maximum flow is 2.0 L min\({}^{-1}\). To measure the flux for each gas, consecutive measurements over time were performed for 10 min, reading gas concentrations every minute, for a total of 10 readings every measurement time. At each incubation time, blank controls concentration was subtracted from the sample concentrations, to remove background noise of atmospheric concentrations of CO\({}_{2}\), N\({}_{2}\)O, and CH\({}_{4}\). Gas concentrations (ppm) were  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Treatment** & & **Soil** & \begin{tabular}{c} **Digestate** \\ **R1** \\ \end{tabular} & \
\begin{tabular}{c} **Digestate** \\ **R2** \\ \end{tabular} &
\begin{tabular}{c} **Biochar** \\ **Water** \\ \end{tabular} \\ \hline Control soil & Control & 0.5 kg & & & 105 mL \\ Soil + 2\% biochar & Bio2\% & 0.5 kg & & 2 g kg\({}^{-1}\) & 105 mL \\ Soil + 10\% Biochar & Bio10\% & 0.5 kg & & 10 g kg\({}^{-1}\) & 105 mL \\ Soil + digestate from pilot R1 & Dig1 & 0.5 kg & 3.8 g kg\({}^{-1}\) & & 115 mL \\ Soil + digestate from pilot R1 + 2\% biochar & Dig1+bio2\% & 0.5 kg & 3.8 g kg\({}^{-1}\) & & 2 g kg\({}^{-1}\) & 115 mL \\ Soil + digestate from pilot R1 + 10\% biochar & Dig1+bio10\% & 0.5 kg & 3.8 g kg\({}^{-1}\) & & 10 g kg\({}^{-1}\) & 115 mL \\ Soil + digestate from pilot R2 & Dig2 & 0.5 kg & & 4.1 g kg\({}^{-1}\) & & 115 mL \\ Soil + digestate from pilot R2 + 2\% biochar & Dig2+bio2\% & 0.5 kg & & 4.1 g kg\({}^{-1}\) & 2 g kg\({}^{-1}\) & 115 mL \\ Soil + digestate from pilot R2 + 10\% biochar & Dig2+bio10\% & 0.5 kg & & 4.1 g kg\({}^{-1}\) & 10 g kg\({}^{-1}\) & 115 mL \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mesocosms set up: soil, digestate and biochar combinations. Biochar was added at concentration of 2 or 10 g kg\({}^{-1}\) of dry soil. Digestate was added in order to obtain an equivalent of 150 Kg N ha\({}^{-1}\). The water added at the beginning of the mesocosoms set up was to keep the soil water content at around 35% of field capacity and to hydrate digestate. Bio, biochar; Dig1, digestate from reactor 1; Dig2, digestate from reactor 2.  
converted to mass per volume units using the Ideal Gas Law, factoring in air temperatures and volumes, and expressed in mmol g\({}^{-1}\) considering the headspace of each flask and the weight of each soil sample [41]. The cumulative curve was calculated by summing concentrations at each incubation time.  
After incubation moisture content (%) was determined gravimetrically and total nitrogen (TN), total carbon (TC), and total organic carbon (TOC), were measured by dry combustion on a Thermo Flash 2000 NC soil analyzer (Fisher Scientific, Waltham, MA, USA) [28]. To this aim, 10 to 20 mg samples were weighed into Ag-foil capsules and pre-treated with 10% HCl until complete removal of carbonates. Soil pH and electrical conductivity (EC) were measured using a digital calibrated pH meter (Hanna-pH211, Padova, Italy) on aqueous extracts (1:20 soil/water ratio).