## 4 Discussion  
### Soil Erosion Risk and Indigenous Farming System  
The soil erosion rate in the research area at each location is very different. This can be explained by the specific terrain and land use type. Our findings indicate that the areas where natural forests are the dominant land cover, soil erosion rates are greater and more serious. As has been noted by some previous research concerning the same natural conditions [9], the grade of slope length is considered to be the main reason for an increased rate of soil erosion in the natural forest. This also has to do with the degradation of these forested areas. The overlapping result of the land use map and the map showing the ratio of sloping indicates that the average slope in the natural forest is 24\({}^{\circ}\). By comparison, the average sloping of cultivated acacia areas and other agricultural land-use areas are 20\({}^{\circ}\) and 17\({}^{\circ}\). In relation to other studies in Vietnam [9; 86], the slope of our research site is significantly higher. It could be considered to be the main reason why there is dramatically high rate of soil erosion. DEMs with different resolutions and accuracies can generate varied topographic and hydrological features, which can, in turn, affect predictions by soil erosion models. Some researchers [87; 88] stated that the LS value grew with the increase of the resolution of DEM data. Another research [89] made a comparison in the changes of LS factor with some DEM resolution from 0.5 m to 100 m and found that the LS with DEM resolution of 30 m is the highest. Our research used the DEM of 30 m. This source could be considered biased in leading to the inference of a very high soil erosion rate. Our findings indicated that the C factor values of IK farming systems are significantly lower than those of NIK at the confidence level of 95% (\(p\)-value \(<\) 0.05) (Table 4). This showed that the IK farming systems can prevent soil erosion rates more effectively than NIK (Table 5). One other benefit of IK farming systems is that when growing acacia, the planting of seeds directly, or with the use of regenerated seeds, other trees and plants species are able to coexist within the naturally acacia plantation. This method leads to a greater health and resilience of that planting area because \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Adaptive Activities** & & **AMs** \\ \hline \multirow{3}{*}{AM1} & \multirow{3}{*}{Adjusting planting calendars} & - & Local rice varieties: early planting to early harvesting \\  & & - & Wet-rice: shortening the growing season \\ \hline \multirow{3}{*}{AM2} & \multirow{3}{*}{Adjusting planting techniques} & - & Acacia: using 2 types of planting including seed-planting and transplanting \\  & & - & Using multiple local varieties of rice in upland farms (name in local: _“mia,” “ba tring”_) \\ \hline \multirow{3}{*}{AM4} & \multirow{3}{*}{Diversifying crops and varieties} & - & Intercropping between acacia and local rice varieties \\  & & - & Intercropping between acacia and cassava \\ \cline{1-1}  & & - & Using 2–3 local varieties \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Private adaptation measures (AMs) used in the farming system. of increased biodiversity. By contrast, using the method of transplanting seedlings, the farmers are required to initially clear the land of all other species. That form of \"clear-cutting\" results in imbalances within the ecosystem and reduces the symbiotic health of the area. As a result, the biodiversity of the area where IK farming systems has been applied is more abundant and influences an increased quality of vegetation than in NIR-farmed areas. It may be noted that our findings coincided with other such studies on biodiversity and indigenous farming systems [90; 91; 92]. The variety of species thus will have an anti-erosion effect through the mechanisms that alter rainfall properties [93].