# Progress and Prospect of Saline-Alkaline Soil Management Technology: A Review
## 4 The New Method of Treating Saline-Alkaline Soil Mainly with Wood Vinegar
### The Source and Application of Wood Vinegar  
As a potential soil conditioner, wood vinegar is a liquid product obtained through a specific process, characterized by its unique composition and properties derived from pyrolytic biomass. Its wide range of raw material sources does provide great flexibility and sustainability for its preparation and application. The raw materials cover many aspects of agroforestry, from crop wastes such as straw, corncobs and sugarcane [105], as shown in Figure 4. These include coconut shell, pistachio shells, cashew shell, olive kernel, walnut shell, etc. [106; 107], as well as forest wastes such as bark, twigs, oak, pine, and driftwood processing residues [108; 109]. The specific component contents of wood vinegar prepared from different materials are shown in Table 1.  
There are many methods for refining wood vinegar, including standing, distillation, freezing and thawing, enzymatic hydrolysis of papaya, ion-exchange resin adsorption, activated carbon adsorption, multi-layer filtration, organic solvent extraction, and electrolysis, among others. To reduce the production cost, the methods typically chosen for refining wood vinegar are standing or distillation [126]. Additionally, crude wood vinegar should be refined according to the intended use with different methods applied based on the specific purpose [127]. The preparation process can be meticulously categorized into four distinct stages: the drying stage, the pre-carbonization stage, the carbonization stage and, ultimately, the calcination stage [128]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{3}{*}{**Materials**} & \multirow{3}{*}{**Materials**} & \multicolumn{4}{c}{**Nature**} \\ \cline{3-6}  & & **pH** & **Density** & **Total Acid** & **References** \\ \cline{3-6}  & & **pH** & **(g cm\({}^{-3}\))** & **Content (\%)** & **References** \\ \hline \multirow{5}{*}{Forestry waste} & _A walnut branch_ & 3.32 & 1.05 & 3.01 & [110] \\  & _FIR trees_ & 2.91 & 1.1014 & 1.84 & [111] \\  & _Rubber Wood_ & 2.9–3.8 & 1.009–1.027 & - & [112] \\  & _Birch Wood_ & 1.8–2.9 & - & - & [113] \\  & _Apple tree_ & 3.94 & 1.005 & 2.64 & [114] \\  & _FIR sawdust_ & 2.3 & 1.1242 & 10.8 & [111] \\  & _Apricot trees_ & 2.93 & 1.05 & 5.38 & [115] \\ \hline \multirow{5}{*}{Crop waste} & _Wheat straw_ & 2.73 & 1.077 & 2.28 & [116] \\  & _Cotton stalk_ & 4.01 & 0.955 & 7.02 & [117] \\  & _Tomato stems_ & 3.21 & 1.0104 & 7.64 & [118] \\  & _Strux_ & 2.43 & 1.05 & 9.29 & [119] \\  & _Soybean straw_ & 2.35 & 1.01 & 16.93 & \\  & _Rice straw_ & 2.93 & 1.025 & 5.56 & [120] \\  & _Corn stalks_ & 2.89 & 1.03 & 6.44 & \\ \hline \multirow{5}{*}{Shell waste} & _Bitter Apricot Shell_ & 2.31 & 1.06 & 6.35 & [121] \\  & _Coconut shell_ & 3 & - & - & [122] \\ \cline{1-1}  & _Durian_ & - & 1.012 & 4.22 & [123] \\ \cline{1-1}  & _Date shells_ & 2.74 & 1.16 & 4.64 & [124] \\ \cline{1-1}  & _Litchi shell_ & 3.17 & 1.04 & 3.69 & [125] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The characteristics related to both structure and composition of wood vinegar from various sources exhibit a diverse range of characteristics, encompassing variations in composition, acidity, and reactivity. Figure 4: The source of wood vinegar. Wood vinegar is used in various applications, including as a fertilizer, insecticide, feed additive, anti-hair loss treatment, and herbicide [129]. It is widely utilized across several sectors, including animal husbandry, agriculture, industry, environmental conservation, food production, and medicine, demonstrating its versatility and significance in multiple facets of our daily life [130; 131]. Some scholars have pointed out that wood vinegar primarily changes the structure of adsorption of heavy metals [132]. The combination of wood vinegar and plant ash or mushroom residue can significantly improve soil nutrient status, promote crop growth, improve root activity, and increase dry matter accumulation [133].