Modelling non-uniform soil water uptake by a single plant root

The assumption of uniform water flow to the root or uniform water potential at the root surface was shown by Hainsworth and Aylmore (1986, 1989) to be erroneous. The present paper demonstrates how the non-uniform uptake of water by a single root can be modeled. Differential equations are numerically solved to describe simultaneous water movement in the plant and in the soil. In the plant, boundary conditions are the water potentials at the root surface (Psi(s)) and in the xylem at the root base (Psi(b)). A set of difference equations describe the flow of water radially through the cortex to the xylem and in the xylem axially upwards to the base. For calculating the water flow in the soil and the values of Psi(s) i.e. the boundary conditions for flow in the root, the finite element method (FEM) is used, the boundary conditions being the flux of water into the plant root and the zero flow across the wall, bottom and surface of a hypothetical soil cylinder surrounding the root.