## 3 Results and Discussions
### Odor Unit  
The logarithmically transformed odor unit values were measured over 21 days to evaluate the effect of biochar application (Table 8). At the beginning of the experiment \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{3}{*}{**Compound**} & \multirow{3}{*}{**Period**} & \multicolumn{4}{c}{**Emission, \(\mu\)g m\({}^{-2}\) Day\({}^{-1}\)**} & \multicolumn{4}{c}{**\(p\)-Value**} \\ \cline{3-8}  & & \multirow{2}{*}{**Control**} & \multicolumn{2}{c}{**Treatment**} & \multirow{2}{*}{**SEM**} & \multicolumn{2}{c}{**5\% Biochar**} & \multicolumn{2}{c}{**10\% Biochar**} \\ \cline{3-8}  & & & & & & & **5\% Biochar** & **10\% Biochar** \\ \hline \multirow{4}{*}{TVFA} & 1 st week & 104.7 & 112.4 & 108.0 & 6.68 & 0.525 & 0.879 \\  & 2 nd week & 166.6 & 81.5 & 89.2 & 56.56 & 0.353 & 0.413 \\  & 3 rd week & 62.9 & 65.5 & 63.4 & 5.25 & 0.878 & 0.996 \\  & Overall & 114.0 & 95.4 & 94.7 & 15.60 & 0.500 & 0.478 \\  & 1 st week & 2628.6 & 2753.2 & 2993.2 & 117.72 & 0.571 & 0.048 \\  & 2 nd week & 1397.4 & 1381.0 & 1408.4 & 51.64 & 0.947 & 0.975 \\  & 3 rd week & 1290.6 & 1400.6 & 1513.1 & 39.85 & 0.073 & 0.003 \\  & Overall & 2049.6 & 2133.0 & 2291.9 & 76.26 & 0.551 & 0.044 \\  & 1 st week & 2.0 & 1.9 & 2.2 & 0.11 & 0.703 & 0.239 \\  & 2 nd week & 2.0 & 3.6 & 2.4 & 0.40 & 0.021 & 0.601 \\  & 3 rd week & 2.4 & 1.9 & 2.2 & 0.12 & 0.018 & 0.328 \\  & Overall & 2.1 & 2.3 & 2.2 & 0.09 & 0.040 & 0.162 \\  & 1 st week & 1.6 & 1.6 & 1.3 & 0.28 & 0.991 & 0.620 \\  & 2 nd week & ND \({}^{\ddagger}\) & ND & ND & - & - & - \\  & 3 rd week & ND & ND & ND & - & - & - \\  & Overall & 0.9 & 0.9 & 0.7 & 0.15 & 0.991 & 0.620 \\ \hline \hline \end{tabular} \({}^{\ddagger}\) ND = Not detected. Note: The number of measurements taken was 18 in the 1 st week, 9 in the 2 nd week, 6 in the 3 rd week, and 33 overall.  
\end{table} 
Table 7: Weekly variations in average emissions of total volatile fatty acid, phenol, \(p\)-cresol, and indole emissions. (day 0), odor unit values in the control and biochar treatments ranged from 2.1 to 2.5. By day 7, odor units had decreased to 1.8-2.0 across all groups, corresponding to an odor reduction of approximately 49.9-68.4% compared to the initial values. The biochar 10% treatment showed a significant 36.1% reduction compared to the control (\(p<0.05\)), while no significant differences were observed in the 5% treatment. From day 14 onward, odor unit values stabilized at approximately 1.4-1.5, reflecting an overall reduction of 80.0-90.0% compared to the initial values. Despite adding fresh manure on days 7 and 14, odor levels remained relatively constant after the second week. By the end of the experiment (day 21), the odor unit values had further decreased to 1.3-1.5, representing a total reduction of 80.0-93.7% from the initial levels. However, no significant differences were observed among the control, biochar 5%, and 10% treatments at this stage, indicating that the biochar's initial effect on odor reduction diminished over time. The observed transient odor reduction can be attributed to the progressive attenuation of the dominant mitigation mechanisms over time. Initially, biochar's porous structure facilitated the adsorption of volatile odorants such as NH\({}_{3}\). At the same time, its low bulk density improved the physical aeration of the bedded pack, thereby inhibiting the formation of anaerobic metabolites like DMS. These synergistic effects--adsorptive and structural--were likely responsible for the significant odor reduction observed during the early phase. However, with continued manure loading, the mitigation efficacy declined. This decrease was likely due to the progressive occupation of biochar's adsorption sites by organic compounds, approaching saturation over time, alongside gradual pore blockage caused by particulate and dissolved organic matter. Such occlusion may have reduced the accessibility of active sorption sites and impaired the biochar's capacity to enhance air diffusion.