## 4 Discussion
### Wind-Induced Soil Erosion
#### 4.1.1 Effect of Biopolymer Type  
The results showed that all tested biopolymer types significantly enhanced the samples' wind erosion resistance on both tested soil types (Figures 4 and 5). When they were applied at their respective plateau concentration, all the biopolymers exhibited dust control effectiveness >99%, with no distinct differences among the tested biopolymer types (Table 3). As can be seen in Table 6, these trends are consistent with most previous research, which also found that all the biopolymers tested significantly improved soil wind erosion resistance and achieved an effectiveness of >90% (with many of them having an effectiveness of >95%). However, some previous studies reported lower effectiveness rates than those in this study and revealed more distinct differences in soil loss among the various tested biopolymer types. These discrepancies can be attributed to differences in the experimental setups. For instance, [PERSON] and [PERSON] [10], [PERSON] et al. [38], and [PERSON] et al. [26] performed wind tunnel tests at significantly higher velocities (20 m/s in [10], 17.6 m/s in [38], and 41.6 m/s in [26]) than this study (13.6 m/s), resulting in higher soil losses and more distinct differences among the tested biopolymer types. Furthermore, some studies employed more challenging testing conditions, such as placing the samples at angles of 25 or 30\({}^{\circ}\) into the test section [23; 24; 26] or incorporating saltation bombardment [13], which revealed more distinct differences among the biopolymer types. While all the tested protein and polysaccharide treatments significantly enhanced the soil's wind erosion resistance, at the lower tested concentrations, the protein-treated samples (FBPC and WP) exhibited noticeably higher soil losses for both the tested soil types than those of the polysaccharides (XG, CS, and CMC) (Figures 4 and 5). As previous wind tunnel studies have not examined the wind erosion resistance of protein-treated soils, this \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Factor**} & \multicolumn{4}{c}{**Medium-Grained Sand**} & \multicolumn{4}{c}{**Fine-Grained Silica Sand**} \\ \cline{2-10}  & **SS** & **df** & **MS** & **F** & \(p\) & **SS** & **df** & **MS** & **F** & \(p\) \\ \hline Type & 6.75 & 4 & 1.69 & 10.5 & \textless{}0.001 & 2.66 & 4 & 0.67 & 5.0 & \textless{}0.05 \\ Application rate & 23.62 & 6 & 5.9 & 36.8 & \textless{}0.001 & 20.90 & 6 & 5.23 & 39.6 & \textless{}0.001 \\ Interaction & 14.79 & 24 & 0.92 & 5.8 & \textless{}0.001 & 7.16 & 24 & 0.45 & 3.4 & \textless{}0.001 \\ Error & 20.07 & 70 & 0.16 & & & 16.50 & 70 & 0.13 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results of two-way ANOVA (\(\alpha=0.05\)) of penetration resistance test data of Phase 2, investigating the effect of the application rate on the crust penetration resistance. observation can only be compared with a previous study investigating the crust strength of biopolymer-treated soil. Here, [PERSON] et al. [9] found that polysaccharide treatments tend to form stronger crusts than proteins do, which is also consistent with the results of the pocket penetrometer tests conducted by this study (Figures 8 and 9). Thus, it is believed that the tested polysaccharides have better inter-particle cohesion, and thus, crust-forming properties than the tested proteins do. Aside from the differences between the biopolymer classes (proteins and polysaccharides), there were also noticeable differences in soil loss among the tested biopolymer types (CMC, CS, XG, FBPC, and WP), especially at the lower tested concentrations. This indicates that not only the biopolymer category (polysaccharide or protein), but also the biopolymer type, significantly affects the wind erosion resistance and is supported by the results of the two-way ANOVA (Table 3). This finding is consistent with the existing literature, which also found that some biopolymer types achieve higher dust control efficiencies than others do (Table A6).