## 3 Results  
### Soil Erosion within the Research Site  
The R factor map was obtained from six hydrometeorology stations around of research site (Figure 3a). The difference of R factor between the locations in the research site is very small, only 3% when comparing the highest and lowest value of this factor within the research site. The lowest value (I320 MJ-mm/ha-h-year) belongs to the Southwest part, while the highest value (1387 MJ-mm/ha-h-year) located in the Northeast corner of the commune. The R factor is shown in Figure 3b. The K value of soil within the region of the commune fluctuated from 0.28 to 0.44 and is shown in Figure 3c. The Arenic Arcrisols have the lowest K value meanwhile the Dystric Fluvisols have the highest value. The K value of Ferralic Acrisols is 0.32. The slope of the research site ranged from zero to over 54 degrees with a mean of 21 degrees. As a result, the topographic factor of the research site is a very complicated aspect, and has high LS value. The highest LS value is concentrated in the Northern part of commune where land use is the natural forest of Bach Ma National Park (BMNP). This factor leads to a very heavy rain flow rate and makes the soil erosion more serious. The LS factor is described in Figure 3d. The results show that the C factor of the research site ranged from 0.01 to 0.59 (Figure 3e). The forest areas have the lowest C value, which means that these areas were deficient in preventing soil erosion. A serial Landsat 8 images in the year of 2019 was downloaded and then adjusted atmospherically and radiometrically to calculate the mean of NDVI, which was then used to measure the C factor. Figure 2: The indigenous knowledge (IK) farming system (**a**); and non-indigenous knowledge (NIK) farming system (**b**). The results indicated that the C factor values of IK farming systems are lower than NIK (in acacia planting areas) significantly at the confidence level of 95% (\(p\)-value \(<\) 0.05). The comparison is shown in Table 4.  
The P factor was created based on the slope map and land use map of Song Kon commune, which was mapped in 2017 and updated in 2019 by Natural Resource and Environment Department of Dong Giang district [40]. In the area where the \(p\)-value is up to 1 it is indicated that the soil erosion process in these areas occurs naturally without any protection measures. The P factor is shown in Figure 3f. The soil erosion rate map is described in Figure 4. This map showed that the lowest soil erosion rate of the Song Kon commune is located in the narrow valley that stretches across the region from the East to the West. The main land use types within the valley are both agricultural and residential areas. In general, the degrees of sloping are not too extreme compared with other areas of the commune. The rate of soil erosion among many specific locations within the commune tends to have a large variation given the terrain conditions. But it is significant that there is an extremely high rate of soil erosion in the most northerly part. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**C Value** & **Mean** & **Degrees of Freedom** & **Sig (\(p\)-Value)** \\ \hline NIK farming system & 0.164 \(\pm\) 0.040 & 29,320.53 & 0.000 \\ IK farming system & 0.150 \(\pm\) 0.041 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The difference of C value between IK and NIK farming systems in acacia planting areas. Figure 3: The component factors of Universal Soil Loss Equation (USLE) in Song Kon commune: (**a**) Location of hydrometeology stations, (**b**) R factor, (**c**) K factor, (**d**) LS factor, (**e**) C factor, and (**f**) P factor. We conducted a comparison of the soil erosion rate within the locations where IK and NIK farming systems were applied. We selected points at the same slope degree (4 levels) and with the same soil type (only Ferralic Arcrisols) for both systems. This was done to synthesize the factors that contribute to the rate of soil erosion.