Effect of root density of wheat and okra on hydraulic properties of an unsaturated compacted loam

Abstract

Root‐induced changes of soil hydraulic properties, that is soil water retention curve (SWRC) and unsaturated hydraulic conductivity (K(ψ)), depend on plant species and root density. This study aimed to investigate the effects of wheat roots and okra roots on both SWRC and K(ψ) of soil within an extended range of matric potential (−300 ~ 0 kPa) and to investigate the effects of root density of wheat (i.e. grass species) and okra (i.e. shrub species) on SWRC and K(ψ) of a loamy soil. The SWRC and K(ψ) of soil planted with wheat and okra were measured by the simplified evaporation method. Soil matric potential was measured directly by high‐capacity tensiometers. Different root densities were obtained by establishing different seeding densities in the soil. Meanwhile, root characteristics in planted soil were obtained using image analysis. The results showed that wheat‐ and okra‐planted soil had significantly larger volumetric water content (VWC) within the range of matric potential from −90 to 0 kPa than that of unplanted soil. Within the range of matric potential from around −300 to −90 kPa, the effects of wheat and okra roots on SWRC were not significant. The effects of wheat and okra roots on K(ψ) were not significant within the range of matric potential from around −300 to −10 kPa. Wheat‐planted soil with a root length density (RLD) of 10.04 cm cm−3 had larger values of VWC (ψ = 0, −33, −50 kPa) than those of wheat‐planted soil with RLD of 2.69 cm cm−3. The difference in hydraulic properties between okra‐planted soil and the two RLDs, 0.89 and 2.96 cm cm−3, was not significant. Okra roots were more effective in increasing saturated water content ( θs) and field capacity ( θfc) than wheat roots. This might be because okra roots are relatively coarser than wheat roots.Highlights Effect of root density of wheat and okra on SWRC and K(ψ) was investigated. The K(ψ) of soil planted with wheat and okra was measured at matric potentials less than −100 kPa. Okra roots were more effective in increasing θs and θfc than wheat roots. Effect of wheat and okra roots on K(ψ) was not significant at matric potentials from −300 to −10 kPa.