Effects of inoculation with Bacillus arenosi on physical and biochemical properties of soil, surface runoff and erosion in degraded forestlands of Northern Iran

A viable practice to improve key properties of soil, and reduce runoff generation and erosion may be inoculation with selected bacteria. However, no previous studies have evaluated whether the direct inoculation of Bacillus arenosi K64 (hereafter simply indicated as B. arenosi) to soil impacts the main physical and biochemical properties of soil as well as the runoff and erosion rates. This study has measured the infiltration rate (IR), tensile strength (TS), mean weight diameter (MWD), polysaccharides (PS) and important enzymes of soil (beta-glucosidase, N-acetyl glucosaminidase, phosphatase and arylsulphatase) in degraded forest soils (Northern Iran) inoculated with B. arenosi in comparison to untreated soils (control). Moreover, the runoff coefficient and soil loss have been measured in plots with soil sampled in those sites under natural rainfalls. IR, TS and MWD increased by 65 % to 160 % in treated soils compared to the control. PS and enzymes were significantly higher (by 20 % to 200 %) after soil inoculation. A noticeable decrease in both surface runoff and soil loss (both by 45 %) in the inoculated soils resulted from those changes. High correlations between the hydrological response of soil on one side, and the measured physical and biochemical variables on the other side were observed. A derivative variable calculated by the Principal Component Analysis can be considered as a meaningful parameter to estimate the changes in soil properties and response due to inoculation with bacteria. Agglomerative Hierarchical Cluster Analysis clearly discriminated the treated from the untreated soils. This study has demonstrated that soil inoculation with B. arenosi plays a significant role in reducing runoff generation and soil erosion under the experimental conditions, thanks to the general improvement in physical and biochemical properties of soil.