## 3 Results
### Spatial Distribution Characteristics of SOM  
As can be seen from the map (Figure 2), the interpolation results for SOM content in the study area ranged from 1.20 to 74.90 g\(\cdot\)kg\({}^{-1}\), with the area in which SOM content was between 5.00 and 15.00 g\(\cdot\)kg\({}^{-1}\) being the largest. Overall, spatial distribution of SOM shows a trend of being high in the middle, and relatively low in the surrounding areas. From the spatial distribution map of SOM content, it is not difficult to see that SOM values are higher in the central and southern mountainous areas of Shandong Province, while it is lower in the south-west and north-west plain areas of Shandong Province, which is related to the topography and land utilization of the study area. Areas with high SOM content are mainly low hills, such as those which border the plains and are susceptible to influxes of surface water and groundwater. These hydrogeological conditions are favorable for the input of organic matter, and also suitable for vegetation growth. The output of organic matter is mainly derived from the decomposition of organic matter by soil microorganisms. Organic matter in these areas decomposes slowly because of their high elevation, low temperature, and sufficient moisture. In addition, the area is distributed with many types of soil, such as cinnamon soil, alluvial soil, and Lime concretion black soil. Some of them have an increased maturity and are relatively rich in SOM content due to a long history of tillage. Lower values were found in the south-western part of Shandong Province. This is because these areas are mainly located in the Yellow River alluvial plain, where the soil texture is \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Indicators** & **Min** & **Max** & **Mean** & \
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} &
\begin{tabular}{c} **Coefficient of** \\ **Variation** \\ \end{tabular} & **Skewness** & **Kurtosis** & \(p\)**-Value** \\ \hline SOM (g\(\cdot\)kg\({}^{-1}\)) & 1.20 & 74.90 & 10.78 & 7.91 & 73.36 & 4.86 & 33.46 & 0.00 \\ Log-transformation & & & & & 0.001 & \(-\)0.106 & 1.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Descriptive Statistics characteristic of SOM content. mainly sandy or has poor water retention, and thus easily undergoes nutrient loss. The accumulation of organic matter can also be affected by uneven precipitation levels. In addition, the north-west of Shandong is located in the hinterland of the Yellow River alluvial plain, and the soil is loam tidal soil. The soil is seriously short of \(p\) and has even less N. The soil is also heavily salinized, with less organic matter content. The spatial distribution of organic matter is different in other regions. In the southern part of the central plain of Jiangsu Province, which is close to Shandong Province, soil organic matter content decreased from north-east to south-west [22]. The amount of organic matter in the southern region is relatively low, which is mainly due to the difference in regional soil-forming environments. The alluvium of the Yangtze River is mainly distributed in the southern region, with light texture, high sand content and lack of adsorption stability mechanisms, none of which is conducive to the accumulation of organic matter. The level of soil organic matter increased gradually from north-west to south-east in Shanxi Province [23]. The north comprises the Loes Plateau, having both a higher altitude and less rain, and consequently soil organic matter content was the lowest here. The south-east has the highest organic matter content because it is mainly brown soil with high precipitation. The central region is mostly tidal soil, which has good fertilizer-retention performance, so its organic matter content was relatively high. In Guangxi Province of southern China, soil organic matter was lower in the south and higher in the north [13]. In northern Guangxi, karst peak cluster depression is the main vegetation type, comprising mostly forest and shrubland.