The hydraulic properties of soil at root-soil interface

Root penetration modifies the soil in the rhizosphere, which affects the transport of water. To study this phenomenon, we developed a soil microcosm for growing roots that allowed our infiltration measurements easy access to the soil. The infiltration of water through small circular areas into the rhizosphere, where roots, had penetrated, and into bulk soil, was measured at negative pressures of -1, -2, and -3 hPa. The infiltration data were used to obtain sorptivity values and an estimate of the hydraulic conductivity of saturated soil. At a given negative pressure, the infiltration of water was less through soil that had been deformed by root growth than through bulk soil. To explain these differences we considered how changes in soil density and the effect of root mucilage might influence infiltration into the soil. Our data suggested that it is the increase in density of the rhizosphere soil that is responsible for the change in its hydraulic properties. In other works, root mucilage has been shown to make the soil water-repellent, but we were unable to confirm that finding in this work. The effect of mucilage on soil may depend on the organic matter content of the soil. Further research in this area is needed.