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 18°C. 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 in the water content range of 0.11 to 0.22 m3 m-3) and λ (0.2-0.7 W m-1 K-1 from 0.05 to 0.22 m3 m-3), and 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 X-ray computed tomography (CT) scanning showed that the SRE-treated samples had a greater proportion of small pores (<60 μm). These changes were attributed mainly to SRE-stimulated microbial activities. HIGHLIGHTS: The effects of incubating a sandy soil with a synthetic root exudate (SRE) on soil physical properties and evaporation are examined.SRE incubation increased the fraction of small pores.SRE incubation increased soil penetrometer resistance and thermal conductivity.Soil hydraulic conductivity was increased in the wet region but was reduced in the dry region.SRE incubation reduced the overall evaporation rate and cumulative water loss.