Propose

Soil organic matter (SOM) content is one critical indicator of agricultural sustainability. Analyzing the spatial distribution and temporal variation of SOM content and its influencing factors at the watershed scale is essential for maintain sustainable soil fertility and productivity in the Chinese Mollisol region.

Materials and methods

A total of 292 soil samples at the same sampling points in 2005 and 2016 were used to quantitatively study the spatial heterogeneity of SOM dynamics in Tongshuang small watershed. Effects of land use types and topographic factors (slope gradient, slope positions, slope aspect, elevations, and topography wetness index (TWI)) on the spatiotemporal distribution of SOM dynamics were investigated.

Results and discussion

The results showed that the variability of SOM content was moderate variation, with an increase rate of 0.21 g kg⁻¹ year⁻¹ from 2005 to 2016. The spatial autocorrelation of SOM content was strengthened by 30.37% in 2016 compared with that in 2005. Slope gradient, slope position, slope aspect, elevations, and TWI had significant effects on the SOM content in 2005 and 2016, but not for the variation of SOM content. The explanatory ability of each factor and their interaction to spatial variability of SOM content was strengthened from 2005 to 2016. Slope gradient and TWI could explain over 8.15% of spatial variability in SOM content.

Conclusion

A combination of slope position with TWI was the dominant interaction factor that explaining at least 16.0% of the SOM distribution. This study is important for the accurate estimation of carbon reserves, sustainable utilization, and management of soil nutrients and to improve soil productivity in the Chinese Mollisol region.