FLOW OF WATER INTO CERAMIC TUBES SIMULATING ROOT SYSTEMS

Abstract

In model root systems constructed of porous ceramic tubing, accumulated outflow volumes of water from four inner tubes, simulating plant roots, surrounded by 12 outer tubes was reduced when spacings narrowed below 2.0 mm in both sandy loam and silt soils. Soil water contents and, simultaneously, capillary conductivity decreased faster at close tube spacings than at wider ones in the order of the decrease at 1.0 mm > at 1.5 mm > at 2.0 mm = that at 3.0 mm = that at 6.0 mm. The ratio of outflow from 12 tubes to that from four, surrounded by the 12, is 3 and constant if all tubes receive water from discrete equal-sized cylinders of soil. At less than 2.0 mm between tubes, the ratio increased with time to maximum of about 9 and 5 for sandy loam and silt loam, respectively, indicating soil cylinder overlap for the particular suction of −0.9 bar imposed on the tubes. At 2.0 mm spacing or greater, the ratio was relatively constant and reasonably close to 3. Radial flow of water may be quickly restricted at root spacings below some limiting distance that is probably dependent upon the demand potential at the soil–root interface.