## 3 Results and Discussions
### Odor Unit
The observed decline in odor mitigation effectiveness over time is supported by previous studies that highlight mechanisms, such as adsorption site saturation, pore blockage, and the finite effectiveness of single biochar applications, that may contribute to such temporal reductions. [PERSON] et al. (2018) observed enhanced odor mitigation through repeated biochar application during swine manure storage. In their 8-week study, bi-weekly surface reapplication of biochar at 2 kg m\({}^{-2}\) yielded superior odor reduction compared to one-time applications at 2 kg m\({}^{-2}\) and 4 kg m\({}^{-2}\). From this, it can be inferred that the continued availability of fresh sorption surfaces may play a critical role in achieving effective odor mitigation. Furthermore, the mechanisms behind the declining efficacy observed in this study are supported by [PERSON] et al. (2018), which demonstrated that biochar's adsorption sites can become saturated when exposed to organic compounds, resulting in a marked reduction in adsorption capacity. A complementary explanation is provided by [PERSON] et al. (2018), who found that biochar aged in plant-root environments experienced significant pore blockage  
\begin{table}
\begin{tabular}{c c c c} \hline
**Elapsed Time** & \multicolumn{3}{c}{**Logarithmically Transformed Odor Unit**} \\
**(Days)** & **Control** & **5\% Biochar** & **10\% Biochar** \\ \hline
0 & 2.3 \(\pm\) 0.1 \({}^{\text{a1}}\) & 2.5 \(\pm\) 0.3 \({}^{\text{a1}}\) & 2.1 \(\pm\) 0.3 \({}^{\text{a1}}\) \\
7 & 2.0 \(\pm\) 0.2 \({}^{\text{a2}}\) & 2.0 \(\pm\) 0.1 \({}^{\text{a2}}\) &  
due to organic exudates and biofilm formation. While mechanistically distinct from direct adsorption site saturation by odorants, this physical occlusion not only limits access to active sorption sites but could also reduce the overall porosity and air permeability of the biochar-amended pack. This multifaceted degradation of biochar's mitigation capabilities--encompassing both reduced active site and impaired physical structure--accounts for the diminished odor reduction observed under continuous manure loading in this lab-scale study. Therefore, under field conditions where manure continuously accumulates, the pores of biochar, which play a key role in NH\({}_{3}\) and DMS adsorption, are likely to become saturated more rapidly. This accelerated saturation could further limit the long-term effectiveness of biochar in mitigating these gaseous emissions in practical dairy bedded pack systems. This highlights the need for strategies to sustain performance, such as periodic reapplication. For instance, given that the 5% biochar application in this study (half the dosage of the 10% treatment) still achieved approximately 63% and 70% of the NH\({}_{3}\) and DMS reduction seen with 10% biochar, a phased approach involving two 5% applications at intervals--effectively matching the total 10% dosage--could be a strategic way to provide fresh adsorption surfaces and potentially maintain higher efficacy over time. Moreover, from a practical and economic perspective, the 5% biochar rate may be more feasible for farmers. Applying 10% biochar by dry weight requires a significantly larger quantity of material and labor, increasing both purchase costs and handling burden. In contrast, the 5% treatment reduces the required volume by half, lowering material costs and making field application more manageable--particularly in large-scale operations. Although its odor mitigation performance is slightly lower, the 5% rate offers a more cost-effective, scalable, and sustainable solution for commercial dairy facilities.