Seasonal dynamics of root growth and desiccation cracks and their effects on soil hydraulic conductivity

Vegetation significantly influences soil hydraulic conductivity, with the extent of this influence depending on root morphology and density, which vary across different developmental stages of plants. This research investigates the interaction dynamics between plant roots (during both growth and decay) and desiccation cracks, as well as the combined impact of vegetation, cracks, and seasonal variations on soil hydraulic conductivity (K_sat). Root growth and decay patterns were observed using a minirhizotron, while changes in crack formation were monitored and interpreted using the Crack Intensity Factor (CIF) for both vegetated and bare areas over an eighteen-month period of wetting and drying cycles. K_sat was analysed based on data from a double-ring test. The findings indicate that the presence of vetiver roots results in a less visible and uneven crack distribution compared to bare soil, with CIF and average crack widths reduced by half. However, cracks reappear during root decay periods. Although cracks were minimised in vegetated soil, K_sat values increased significantly during dry periods, with a 16-fold rise in the vegetated zone due to root propagation, while the bare zone showed a marginal 5-fold increase. The presence of cracks and roots significantly influences K_sat, exhibiting distinct hysteresis behaviour in response to drying and wetting cycles.