Model for water infiltration in vegetated soil with preferential flow oriented by plant roots

Purpose
There is strong experimental evidence that root systems substantially change the hydraulic properties of soil. However, the mechanisms by which they do this remain largely unknown. In this work, we made the hypothesis that a preferential flow of soil moisture occurs in directions which follow the orientation and distribution of roots within the soil, and that this phenomenon alters soil moisture flow patterns.

Methods
We modified Richards’ equation to incorporate root-oriented preferential flow of soil moisture. Using the finite element method and Bayesian optimisation, we developed a pipeline to calibrate our model with respect to a given root system.

Results
When applied to simulated root distributions, our model produced pore-water pressure profiles which agreed with those derived from experimental saturated hydraulic conductivity values of soils vegetated with willow and grass. Agreement improved for simulated root distributions where root segments were oriented in a more realistic way, suggesting that the hydraulic characteristics of vegetated soils are a consequence of root-oriented preferential flow.

Conclusion
By incorporating root-oriented preferential flow, our model improves the ability to describe and analyse water infiltration through vegetated soil. This could help optimise irrigation, forecast flood events and plan landslide prevention strategies.