## 2 Materials and Methods
### Properties of Raw Materials  
The properties of the dairy manure, sawdust, and their mixture used in this study are presented in Table 1. The nitrogen and carbon contents of the samples were measured using an automatic elemental analyzer (FLASH 2000, Thermo Fisher Scientific, Waltham, MA, USA). The samples' moisture content was measured by drying them at 105 \({}^{\circ}\)C for 24 h. The volatile solid (VS) content was analyzed by combusting the dried samples at 550 \({}^{\circ}\)C for 8 h. The wet bulk density of the samples was determined by measuring their weight and volume using a 1 L stainless steel bucket. The free air space (FAS) within the samples was calculated using the air-filled porosity equation presented by [PERSON] et al. (2018).  
The biochar used in this study, derived from rice husk through pyrolysis at 550 \({}^{\circ}\)C, was characterized as shown in Table 2. Thermogravimetric Analysis (TGA) was performed using a Thermal Analyzer (TGA 2, Mettler Toledo, Columbus, OH, USA) to determine the moisture and volatile solid content of the biochar. The TGA was conducted within a temperature range of 25 \({}^{\circ}\)C to 950 \({}^{\circ}\)C at a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\). The nitrogen and carbon contents of rice husk biochar were measured using an automatic elemental analyzer (FLASH 2000, Thermo Fisher Scientific, Waltham, MA, USA). The pH of the rice husk biochar was analyzed using a pH meter (Orion 4 Star, Thermo Scientific, MA, USA). The mixing ratio of biochar to deionized water and the equilibrium time after mixing followed the methods suggested in previous literature ([PERSON] _et al._, 2018). Biochar pore properties were analyzed using a surface area analyzer (ASAP 2420, Micrometrics Instrument Corporation, Norcross, GA, USA) with N\({}_{2}\) as the purge gas at 77 K. Specific surface area was calculated using the Brunauer-Emmett-Teller method ([PERSON], 2010). Total pore volume was estimated from single-point adsorption at a relative pressure (P/P\({}_{0}\)) of about 0.99. The micropore surface area and micropore volume of biochar were obtained using the t-plot method ([PERSON], 2010). The pore size distribution and average pore diameter were obtained through the Barrett-Joyner-Halenda method using the adsorption branch ([PERSON], 2010). To investigate the surface morphological property and chemical composition of rice husk biochar, field-emission scanning electron microscopy (FE-SEM; CLARA, TESCAN, Brno, Czech Republic) coupled with energy-dispersive x-ray spectroscopy (EDS; Ultim Max, Oxford Instruments, Abingdon, United Kingdom) was used. The surface chemical structure of rice husk biochar was analyzed using an infrared spectrometer with a diamond ATR tip (Alpha-P, Bruker, Billerica, MA, USA) in the range of 400-4000 cm\({}^{-1}\).  
\begin{table}
\begin{tabular}{l c c c} \hline
**Property** & **Dairy Manure** & **Sawdust** & **Mixture** \\ \hline Moisture content (\% w.b.) \({}^{\ddagger}\) & 79.1 \(\pm\) 0.2 & 12.9 \(\pm\) 0.3 & 75.0 \(\pm\) 0.5 \\ Volatile solid (\% d.b.) \({}^{\ddagger}\) & 83.0 \(\pm\) 0.5 & 98.3 \(\pm\) 0.1 & 90.9 \(\pm\) 0.2 \\ Total nitrogen (\%, w.b.) & 0.5 \(\pm\) 0.0 & 0.2 \(\pm\) 0.0 & 0.5 \(\pm\) 0.0 \\ Total carbon (\%, w.b.) & 7.0 \(\pm\) 0.3 & 47.8 \(\pm\) 0.0 & 10.0 \(\pm\) 0.0 \\ C/N ratio & 14.2 \(\pm\) 0.8 & 207.5 \(\pm\) 0.0 & 21.1 \(\pm\) 0.0 \\ Bulk density (g L\({}^{-1}\)) & 956.8 & 108.0 & 613.0 \(\pm\) 5.3 \\ Free air space (\%) & 12.6 & 92.8 & 45.1 \(\pm\) 0.5 \\ \hline \end{tabular} \({}^{\dagger}\) w.b. = Wet basis; \({}^{\ddagger}\) d.b. = Dry basis.  
\end{table}
Table 1: Characteristics of dairy manure, sawdust, and their mixture. (Mean \(\pm\) S.D., \(n\) = 3).