# Application of Lignin for Slope Bioengineering: Effect on Soil Improvement and Plant Growth
## 2 Literature Review
[40] explored xanthan and \(\beta\)-glucan gums with red-yellow soil and reported that biopolymer-treated soil promoted the soil environment for vegetation growth. [PERSON] et al. [41] used xanthan, guar, agar, and beta-glucan gums in laboratory experiments with clayey soil and reported that these biopolymers promoted vegetation growth and improved seed germination. Using field studies, [PERSON] and [PERSON] [42; 43] revealed that biopolymers such as xanthan gum, guar gum, and agar gum were sustainable materials for promoting surface vegetation growth. [PERSON] et al. [44] observed that biopolymer-treated river sand slopes with grass increased slope stability and erosion resistance. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Soil Type** & **Biopolymers** & **Content (\%)** & **Method** & **Vegetation** & **Curing** & **Outcomes** & **Reference** \\ \hline Sand & Lignin-(guaiac, syring, \(p\)-hydroxy phenyl) & 2 & Mixing— spraying & _Agriophyll_ & & The lignin biopolymer and & \\  & & & & _squarrosum, Artemisia_ & & the species used could form & \\  & & & & _Aretemisia_ & & a community within 2 to 3 & \\  & & & & _desertorum_ & & years and stabilize the & \\  & & & & _Spreng, etc._ & & desert dune significantly. & \\ \hline Red–yellow sand & Xanthan gum, \(\beta\)-glucan & 0.5 & Mixing & _Oats (600 seeds)_ & 7-21 & Xanthan gum and \(\beta\)-glucan & \\  & & & & _sets (600 seeds)_ & & biopolymers estimated & \\  & & & & & & seed germination and & \\  & & & & & & & \\ \hline Granular soil & IPCs, HPAN, \(\beta\)-chromadec, KNO\({}_{3}\) & 1–2 wt.\% & Mixing & _Sudan grass_ & 1095–1460 & \begin{tabular}{c} IPCs offer a considerable \\ soil binder and enhance \\ grass growth compared to \\ the other polymers. \\ \end{tabular} & \begin{tabular}{c} [PERSON] et al. \\ [35] \\ \end{tabular} \\ \hline Clayey soil & Xanthan gum, \(\beta\)-chromadec, guar gum, agar gum, beta-glucan & 0.25, 0.5, 1 & Mixing & _Oats (160 seeds)_ & 2–14 & \begin{tabular}{c} Xanthan gum efficiently \\ promotes vegetation growth \\ and increases the seed \\ germination ratio by about \\ 300\% at 0.5\% compared to \\ other biopolymers. \\ \end{tabular} & \begin{tabular}{c} [PERSON] et al. \\ [40] \\ \end{tabular} \\ \hline Silt & Xanthan gum, \(\beta\)-chromadec, guar gum, agar gum & 0.5 & Mixing & _Ryagrass_ & 7, 14, 21, 28 & \begin{tabular}{c} Xanthan gum-treated silt \\ has the highest growth and \\ germination rate compared to guar- and \\ agar-treated silt. \\ \end{tabular} & \begin{tabular}{c} [PERSON] et al. \\ [44] \\ \end{tabular} \\ \hline Sand & Xanthan gum-starch & 0.5 & Spraying & _Turfgrasses_ & 16 & \
\begin{tabular}{c} Xanthan gum enhanced \\ water retention, soil \\ cohesion, and vegetation \\ growth to improve erosion \\ resistance. \\ \end{tabular} &
\begin{tabular}{c} [PERSON] et al. \\ [33] \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of studies on biopolymer and vegetation growth. A recent review study by [PERSON] and [PERSON] [45] summarized advances in the use of lignin in agriculture to stimulate plant development; however, only limited research on the effect of lignin on vegetation growth in relation to slope bioengineering has been conducted to date. A recent study [34] showed that lignin could play a significant role in soil-plant interactions and improve vegetation growth within 2 to 3 years, helping to stabilize desert dunes. However, due to the limited research, the effect of lignin on seed germination and vegetation growth remains unclear and needs further investigation.