## 3 Results and Analysis  
### Analysis of Nutrient Features  
In Table 3, the pH of tobacco planting soil in seven towns of Debao County is generally between 6.1 and 7.8, with an average value of about 6.9, which is generally weak acidity. The content of soil organic matter is between 12.1 and 49.3 g/kg, with an average value of 27.5 g/kg, which is moderate, while the average content of organic matter in Najia Town, Zurong Town and Du'an Town is 38.0, 33.5 and 32.5 g/kg, respectively, which is within the high range. The average contents of soil total N, available K and available P are 1250, 270.5 and 23.0 mg/kg. Among them, the content of soil total N and available P is in a moderate state, and available K is in a high state.  
Figure 3 shows that the exchangeable Ca content in the tobacco planting soil in seven towns of Debao County is relatively high, with more than 47% of the soil samples containing >4 cmol/kg and 22% of the soil samples containing >10 cmol/kg, which is extremely high. The exchangeable Mg content of soil is good, and the content of most samples is between 0.8 and 1.6 cmol/kg, which is basically within the suitable range for planting high-quality tobacco. The number of soil samples with available B content lower than the B deficiency threshold (0.5 mg/kg) [34] accounted for about 35%, and the number of samples with available Zn content higher than the enrichment threshold (1.0 mg/kg) accounted for about 99.5%. Therefore, the soil available Zn content is very high, but the available B content is slightly insufficient.  
Figure 2: The LightGBM modeling process framework.  
_Appl. Sci._**2022**, _12_, 12354  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Nutrient** & **Town** & **Range** & **Average** & **Standard** & **Variation** \\
**Factors** & **Town** & **Value** & **Average** & **Deviation** & **Coefficient** \\ \hline  & Yantong & 6.4–7.2 & 6.8 & 0.19 & 2.84 \\  & Longguang & 6.3–7.1 & 6.8 & 0.22 & 3.32 \\  & Najia & 6.6–7.4 & 7.2 & 0.21 & 2.99 \\ pH value & Zurong & 6.6–7.5 & 7.2 & 0.22 & 3.03 \\  & Du’an & 7.4–7.8 & 7.6 & 0.10 & 1.27 \\  & Dongling & 7.0–7.6 & 7.4 & 0.19 & 2.55 \\  & Jingde & 6.1–7.3 & 6.7 & 0.26 & 3.87 \\  & Total & 6.1–7.8 & 6.9 & 0.35 & 4.99 \\  & Yantong & 12.8–57.0 & 25.2 & 8.14 & 32.34 \\  & Longguang & 23.0–39.4 & 28.8 & 5.64 & 19.58 \\  & Najia & 29.2–49.3 & 38.0 & 4.492 & 11.83 \\ Organic matter & Zurong & 20.6–48.8 & 33.5 & 7.72 & 23.06 \\ (g/kg) & Du’an & 26.9–41.7 & 32.3 & 4.12 & 12.78 \\  & Dongling & 14.2–44.1 & 24.0 & 9.32 & 38.89 \\  & Jingde & 12.1–39.0 & 25.1 & 5.0 & 19.97 \\  & Total & 12.1–49.3 & 27.5 & 7.37 & 24.99 \\  & Yantong & 50–2020 & 930 & 460 & 49.03 \\  & Longguang & 530–2560 & 1420 & 519 & 36.64 \\  & Najia & 990–3380 & 1730 & 671 & 38.68 \\ Total nitrogen & Zurong & 610–2620 & 1680 & 500 & 30.28 \\ (mg/kg) & Du’an & 7601520 & 1170 & 177 & 15.20 \\  & Dongling & 190–1860 & 840 & 532 & 63.65 \\  & Jingde & 100–3210 & 970 & 356 & 36.51 \\  & Total & 50–3380 & 1120 & 516 & 41.31 \\  & Yantong & 37.3–472.5 & 231.1 & 96.38 & 41.71 \\  & Longguang & 48.1–298.2 & 171.2 & 78.09 & 45.61 \\  & Najia & 91.8–298.2 & 183.4 & 53.32 & 29.07 \\ Available K & Zurong & 57.8–298.0 & 206.7 & 63.29 & 30.61 \\ (mg/kg) & Du’an & 222.3–364.8 & 299.0 & 47.32 & 15.82 \\  & Dongling & 206.8–379.7 & 287.0 & 60.20 & 20.98 \\  & Jingde & 49.4–504.8 & 308.8 & 81.89 & 26.86 \\  & Total & 37.3–504.8 & 270.5 & 93.60 & 38.84 \\  & Yantong & 3.8–82.3 & 31.1 & 20.21 & 64.96 \\  & Longguang & 4.6–44.1 & 22.5 & 11.52 & 51.28 \\  & Najia & 6.6–60.9 & 25.8 & 17.35 & 67.38 \\ Available P & Zurong & 9.8–62.5 & 26.1 & 12.38 & 47.46 \\ (mg/kg) & Du’an & 14.8–41.9 & 25.1 & 7.75 & 30.89 \\  & Dongling & 9.8–32.1 & 19.6 & 7.18 & 36.68 \\  & Jingde & 4.2–60.0 & 19.4 & 10.88 & 56.01 \\  & Total & 3.8–62.5 & 23.0 & 14.03 & 57.97 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Soil pH values, organic matter, total N, available K, available P content in seven tobacco planting towns of Debao County.