Physical properties of a sandy soil as affected by incubation with a synthetic root exudate - strength, thermal and hydraulic conductivity, and evaporation

Plant roots release various organic materials that may modify soil structure and affect heat and mass transfer processes. The objective of this study was to determine the effects of a synthetic root exudate (SRE) on penetrometer resistance (PR), thermal conductivity (λ), hydraulic conductivity (k) and evaporation of water in a sandy soil. Soil samples, mixed with either distilled water or the SRE, were packed into columns at a designated bulk density and water content, and incubated for 7 days at 18oC. Soil PR, λ, k and evaporation rate were monitored during drying processes. Compared with those incubated with water, samples incubated with SRE had visible hyphae, greater PR (0.7-5.5 MPa higher) and λ (0.2-0.7 W m-1 K-1 higher) in the water content range of 0.11-0.22 and 0.05-0.22 m3 m-3, increased k in the wet region but decreased k in the dry region. SRE treatment also reduced the overall soil water evaporation rate and cumulative water loss. Analysis of CT scanning showed that the SRE treated samples had a greater proportion of small pores (< 60 m). These changes were attributed mainly to SRE-simulated microbial activities.