Non-uniform soil water extaction by plant roots

Using the technique of Computer Assisted Tomography applied to gamma ray attenuation measurement of soil water content, it has been shown that the assumption of uniform absorption of soil water along a plant root is clearly erroneous and that drawdown distance is a function of time. The results suggest that the plant sequentially removes water from the top to the bottom of the root as soil hydraulic resistance becomes a major limiting factor in the upper layers, even at the high soil water potential (–0.30 MPa) used.