Forest soil inoculation with Bacillus subtilus reduces soil detachment rate to mitigate rill erosion

Rill erosion is one of the most important types of soil erosion that has caused the destruction of many lands in recent decades, and its management has become an essential issue in world research. This study has evaluated the effects of soil physical properties induced by Bacillus subtilis OSU 142 (B. subtilis) on the soil detachment rate (Dc) and rill erodibility (Kr) in the inoculated soil, compared to the uninoculated soil in rill erosion-prone areas of Northern Iran. For measuring Dc, a hydraulic flume was used at 5 slopes (from 4.3% to 34.2%) and 5 water discharges (from 0.31 l m-1 s-1 to 0.67 l m-1 s-1) with 7 replications. Moreover, three physical properties of soils including the bulk density, mean weight diameter and total porosity of soils were measured before and after inoculation. Dc was found to be significantly lower (on average -52% for the average slopes) in the inoculated soil with the B. subtilis (IB) compared to the uninoculated soil (UB). Rill erodibility (Kr), also was notably reduced in the IB soil (-70%) relative to the UB soil. The variability of Dc in the two studied soils showed a positive correlation to bulk density (R2 = 0.87), and a negative correlation to mean weight diameter (P < 0.01) (R2 = 0.89). The clustering of soils in two distinct classes (inoculated and uninoculated) by agglomerative hierarchical cluster analysis (AHCA) revealed a clear difference based on the physical properties of the treated and control soils. Based on the findings of present study, direct inoculation of B. subtilis can be proposed as a new and suitable technique for the improvement of soil physical properties and the reduction of soil detachment rate, especially in rill erosion-prone areas.