Soil surface roughness of sloping croplands affected by land degradation degree and residual of incorporated straw

Changes in soil surface roughness (SSR) are not only closely associated with the characteristics of the underlying surface but also play a vital role in hydrological and soil erosion processes. SSR of degraded croplands is likely affected by the residual of incorporated straw, however, few studies have been focused on this topic. This study was conducted to investigate the changes in SSR of sloping croplands with different land degradation degrees under straw incorporated and without straw incorporated treatments, and determine the dominant factors attributing to these changes in the black soil region of Northeast China. SSR was determined by a photogrammetry technique and the dominant influencing factors were identified by redundancy analysis. The results showed that SSR were decaying by land degradation. Compared to non-degraded croplands, SSR of light, moderate and heavy degraded croplands decreased by 10.4 %, 11.3 %, 23.3 % and 13.8 %, 16.7 %, 31.9 % for straw incorporated and without straw incorporated treatments, respectively. The improvement of SSR was mediated by residual of incorporated straw. Compared to the treatment of without straw incorporation, SSR of straw incorporated treatment increased by 29.4 %, 30.5 %, 32.7 %, and 33.3 % for non, light, moderate and heavy degraded croplands, respectively. Change in SSR was modulated by soil properties, crop characteristics, and residual of incorporated straw. Change of SSR was dominantly controlled by water-stable aggregate (WSA), penetration resistance (PR), soil organic matter (SOM), structure stability index (SSI), mean weight diameter (MWD), root mass density (RMD), litter mass density (LMD) and amount of incorporated straw residual. The increase in SSR was linear with SSI, SOM, RMD and LMD, and logarithmic with MWD and WSA. The measured SSR could be well estimated by WSA, SOM, PR and RMD (R2 = 0.82). SSR could affect hydrological and erosion processes of croplands by reducing sediment connectivity and increasing land surface storage of runoff. The results of this study are helpful in understanding the spatial heterogeneity of SSR at the hillslope scale.