Background The soil erodibility (K factor) is one of the key factors in calculating soil erosion modulus using the Chinese soil loss equation (CSLE). Therefore, obtaining an accurate distribution map of K factor is necessary for the national monitoring of soil and water loss in China. The current available Chinese K factor map was made during the soil and water conservation measures survey in the first national census in 2011, based on soil type maps of provinces (autonomous regions and municipalities) and soil profile data from the second national soil survey (K value in version 2011 for short). It is necessary to update the K value in the version 2011 and study the changing characteristics of K factor from the version 2011 to the version 2022 (see below).

Methods In order to increase the accuracy and reliability of soil erosion assessment, an updated K factor map was completed in 2022, using the random forest prediction method and soil profile data from the "Investigation of Chinese Soil Series" (K value in version 2022 for short). The K factor maps in the version 2011 and 2022 were chosen as the research projects, and their value size and spatial distribution in the major river basins and soil type of China were compared.

Results 1) The mean value of the national K value in the version 2022 (0.029 8 t·hm²·h/(MJ·mm·hm²)) was slightly lower than that in the version 2011 (0.032 3 t·hm²·h/(MJ·mm·hm²)), indicating a positive trend in the development of soil erosion control in China. Except for the Haihe River Basin and Songliao River Basin, the K value in the version 2022 in each basin increased when compared to the K value in the version 2011. Among them, the K factor of castanozems, dark brown earths, saline soils and other soil type decreased the most, while the K factor of fluvo aquic soils, cinnamon soils, yellow earths and other types of soil increased. 2) The trend of changes in the national mean value of K factor was consistent with the dynamic trend of a decrease in the area and degree of soil erosion nationwide. The decrease in K factor was mainly related to reasons such as Returning Farmland to Forests and soil amendment, while the increase in K factor was related to intensive cultivation and slope erosion.

Conclusions This study may provide a basis for dynamic monitoring of soil erosion and evaluation of the effectiveness of soil and water conservation management. In the future, it is necessary to strengthen ecological protection, improve soil quality and its ability to resist erosion.