The pullout resistance of plant roots in the field at different soil water conditions and root geometries

Root anchoring in the soil provides significant resistance for trees to resist against the wind and potential soil shear failure in a slope. Soil conditions and root properties affect pullout resistance of plant roots in the soil, which govern the anchoring capacity of plants. Soil water conditions may change considerably during rainfalls and affect the anchoring capacity of plant roots. Therefore, research on the effect of soil water conditions on plant roots' pullout behavior is essential to better understand the anchoring of plants in the soil during rainfall. In-situ pullout tests on roots of Paper Mulberry are carried out at various soil water conditions. Significant findings in this research are: (1) the initial pullout stiffness decreases with root length and soil water content; (2) increase in soil water contents causes a noticeable reduction in the soil-root bond strength; (3) the soil-root bond strength decreases with root length; (4) the pullout resistance for roots tested in the field takes into account root branching and interlocking of root hairs with surrounding undisturbed soils.