In order to ascertain the impacts of microorganism (bacillus subtilis) on soil improvement and water movement in saline alkali soil

a laboratory 1D infiltration experiment of brackish water with different concentrations (0 g/L

1 g/L

2 g/L

3 g/L and 4 g/L) was conducted. The results showed that

bacillus subtilis reduced the infiltration capacity of the soil significantly

and slowed down the water flow. Compared with the control

the cumulative infiltration and the final wetting front distance were significantly decreased in soil with bacillus subtilis. The reduction in the cumulative infiltration was up to 40.97% under the brackish water concentration of 2 g/L. The wetting front distance showed the similar results as infiltration. Then

Philip and Kostiakov infiltration model were used

and the fitting result showed that the imbibition rate S of Philip formula was less than that in the corresponding control groups. This suggested the diminished solid water absorbing ability of capillary force might be due to the viscosity property improvement made by bacillus subtilis. The experience coefficient K of Kostiakov formula was smaller than the control

which indicated that the initial infiltration rate of bacillus subtilis contained solid was lower. Nevertheless

the empirical exponential β was greater than the control

demonstrating that the containing solid capacity of bacillus subtilis was fading with the increasing infiltration time. After the infiltration of brackish water

the soil with bacillus subtilis showed a better aggregate structure

which could significantly improve the ventilation and water holding capacity. Soil water characteristic curve showed that

with the same moisture content and concentration

the water suction of the bacillus subtilis containing solid was stronger than the corresponding control

with more reduced matrix potential

which indicated that bacillus subtilis increase the water holding capacity and inhibit the water evaporation and infiltration. Finally

the water characteristic curve was fitted using van Genuchten model. In this formula

the soil residual water content

saturated water content and coefficient associated with intake value increased

and shape coefficient decreased. In conclusion

bacillus subtilis can improve the solid structure effectively and reduce solid infiltration. This study could provide a theoretical support for the microorganism application in soil improvement.