Assessing the Effects of Plant Roots on Soil Water Infiltration Using Dyes and Hydrus-1D

Abstract

Forestry eco-hydrology is closely related to root architecture, and soil water infiltration has been always associated with root architecture. In this study, dye infiltration experiments and HYDRUS-1D were used to quantify the effects of different root architectures on the dynamics of soil water infiltration, volumetric water content, and soil water pressure head. The results provide evidence that root channels acted as preferential flow paths for water infiltration and percolation into the soil. Maize fibrous roots, rubber trees fine roots, and Spartina alterniflora smooth roots easily penetrated the plough layer of an agriculture site, the hard soil layer of a forest site, and the alternating sandy and mud layers of an intertidal zone, respectively. The initial and final infiltration rates were significantly different between the rooted and rootless soil profiles. The root-induced infiltration events lowered the propagation time of the wetting front across the rooted soil profile by 33%–113% than the rootless soil (p < 0.05), and the volumetric water content of the saturation zone of the rooted soil profile increased by 12%–19% relative to the rootless soil (p < 0.05). Furthermore, the soil water pressure head increased from negative (i.e., unsaturated) to positive (i.e., saturated) in the saturated soil. This change was more pronounced in the maize fibrous roots soil profile, but less pronounced in the rubber fine roots’ soil profiles or the S. alterniflora smooth roots. The results indicate that the downward movement, volumetric water content, and soil water pressure head were higher in soil profiles having plant roots than the rootless soil, and the degree of roots effects depended on roots architectures, soil hardness, and soil layer configuration. The findings provide evidence that root channels can act as preferential flow paths for water infiltration and percolation into the soil.