The influence of soil water content on the uptake of ions by roots. I. Soil water content gradients near a plane of onion roots.
Water content and ion concentration gradients were measured in soil near a plane of onion seedling roots. Using the water content-matric potential relation for this soil, the water content gradients were transformed into matric potential gradients. Potential gradients near the roots were steeper in drier soil. In the driest soil, which was initially at -3 bar, the potential at the root surface fell to about -20 bar. However, it was shown that if the root-soil geometry had been radial rather than linear, the potential at the root surface would have been about -3.5 bar, which supported the view that steep potential gradients do not normally occur near roots.