The effect of root shrinkage on soil water inflow

As a soil dries, the roots growing in it may shrink and retain only partial contact with the soil. The steady-state model described here calculates the effect of root shrinkage on the water inflow across soils and roots with various hydraulic conductivities. Relative to standard conditions, typical of a secondary root in a loam at field capacity, the water inflow was very sensitive to the root radius, the root shrinkage, the root hydraulic conductivity and the water potential in the bulk soil and at the root endodermis. The inflow was insensitive to the density of rooting, and to the soil hydraulic conductivity except in dry sandy soil where this was lower than the root hydraulic conductivity. Loss of full contact can decrease the inflow by a factor of up to about three. In very dry conditions, vapour transfer across the air gap between the root and soil surfaces can contribute usefully to the total water inflow.