Potential of urease producing bacteria on biological stabilization and prevention of soil erosion

Soil is considered one of the most valuable natural resources and the existence of life on the surface of the earth depends on the existence of soil in addition to water and air. Soil stability is an important factor in the health of the soil system and it is a prerequisite to perform processes such as the cycle of elements in the soil. Soil erosion is a serious problem and threat in different regions of the world, and therefore protecting and preventing soil erosion as a non-renewable natural resource is of high priority. To prevent soil erosion, there are various physical, mechanical, and chemical methods.  Due to their high cost and harmful effects on the environment, today much attention is paid to biological methods that are friendly to the environment. This study aimed to investigate the potential of urease producing bacteria on biological stabilization and prevention of soil erosion.

Soil samples were collected from the Bazoft area in Chaharmahal va Bakhtiari provinces and transported to the laboratory. The enrichment and selective method was used to screen urease producing bacteria in the urea agar base culture medium. The activity of the urease was investigated by the electrical conductivity method and three strains with the highest urease activity were selected and used in further steps. The selected strains were identified by molecular methods, colony PCR by using 14f and 1492r universal primers, and sequencing. The compressive and shear strength was estimated in inoculated soils after 14 days.  The wind erosion threshold velocity was measured in the wind tunnel. The soil loss was estimated at different wind speeds (17.3, 22.09, and 27/20 m/s) in the inoculated soils.

The urease-producing bacteria were identified by changing the color of the culture medium from yellow to pink. The results showed that the soils of this area have a high potential for urease producing bacteria. Three species were selected based on their urease activity and identified as Bacillus thuringiensis (RIFR-U3), Bacillus sp. (RIFR-U7), and Exiguobacterium sp. (RIFR-U10). The compressive and shear strength increased in soil inoculated with the selected bacteria compared to the control.  The highest compressive (1.56± 0.241 kg/cm2) and shear strength (2.066±0.18 kg/cm2) were detected in the soils inoculated with Bacillus sp. (RIFR-U7) and Exiguobacterium sp. (RIFR-U10) strains, respectively. The wind erosion threshold velocity was 12.19 m/s. The soil loss was less in the inoculated soils with bacteria compared to control and Bacillus sp. (RIFR-U7) had the highest efficiency in preventing soil loss.

The increased compressive and shear strength showed that these selected strains are moderate to good stabilizers for increasing compressive strength and very good for increasing shear strength. The wind tunnel results showed that Bacillus sp. (RIFR-U7) inoculated soil was more resistant to wind erosion compared to the other two strains and controls. In conclusion, it seems that different strains or a combination of them can be used based on what characteristic of the soil is to be improved or the purpose of resistance against which erosion.