Improving and correcting unsaturated soil hydraulic properties with plant parameters for agriculture and bioengineered slopes

The presence of vegetation in the upper layer of vadose zone results in complex moisture dynamics (soil-root-water interaction) due to the combined effects of transpiration and soil water evaporation. Unsaturated soil-root composite hydraulic properties, transpiration and soil water evaporation and effect of plant parameters (i.e., leaf area index (LAI), root length density (RLD) and root area index (RAI)) on soil property are keys for understanding this complex moisture dynamics. Previous studies have not collectively discussed these plant parameters and unsaturated soil properties to understand moisture dynamics in the vadose zone. The main objective of this review is to identify the gaps and lay out future studies that need to be addressed between unsaturated soil mechanics and plant parameters. These gaps are discussed in the context of agricultural field and bioengineered slopes (a type of slope remediation). The hydraulic properties of soil-root composite (water retention curve, hydraulic conductivity) are discussed with respect to soil composition, soil density and cracked soil. Influences of plant parameters, such as LAI, RLD and RAI on boundary conditions are discussed. For scheduling irrigation schemes and analyzing crop yield and water use efficiency, bare soil hydraulic properties were incorporated instead of rooted soil hydraulic properties by previous researchers. For analyzing the stability of bioengineered slopes, plant parameter influence was not taken into account. The efficacy of soil-root composite water retention curve (SRCWRC) incorporation in the field of agriculture as well as geotechnical engineering (i.e., for bioengineered slope stability analysis), is demonstrated in this review. The study proposes the incorporation of aging effect of plants, temporal variation of root distribution and consideration of LAI variation with altitude; in applications related to both agricultural field and bioengineered slope stabilization.