Microbial Effects on Hydraulic Properties of Sewage Sludge-Induced Water-Repellent Soil.

Soil water repellency (SWR) is a widespread natural phenomenon that results from a complex interplay between the hydrosphere, lithosphere, biosphere, atmosphere, and anthroposphere. Sewage sludge application can induce soil water repellency (SWR), impacting soil hydraulic properties. This research examined the effect of soil microbial manipulation (removal and addition) on SWR and water retention in a silty-clay-loam soil amended with varying sludge amounts. Three levels of water repellency (zero, weak and strong) were artificially created in a silty clay loam soil by adding urban sewage sludge. The results showed that the elimination of soil microorganisms such as fungi and bacteria and their interactions significantly (P≤0.01) affect the hydrophobicity, soil water retention curve (both wetting and drying) of the sludge-treated soils. Microbial exclusion significantly reduced SWR (21-49%), suggesting that microbial activity contributes to the formation of hydrophobic compounds. Conversely, microbial inoculation increased SWR (27.5-50%), indicating microbial production or transformation of hydrophobic substances. It is concluded that soil microorganisms can increase soil water repellency. Also, soil microorganisms can affect the soil water retention curve through their influence on soil water holding capacity, depending on microbial diversity. These findings highlight the critical influence of microbial activity on SWR and water holding capacity in sludge-treated soils.