Abstract
The purpose of this investigation was to estimate the root resistances to water movement. The total root resistances and the root conductive resistances were measured using the pressure chamber method and the siphon method, respectively. The absorptive resistances were calculated from the measured resistances assuming a simple model of a root system. The results are summarized as follows. 1) The total root resistance changes with the flow rate from the root base. The result suggests that the resistance changes with the transpiration rate. The resistance decreases as the water absorptive rate from the root increases and converges to a constant value. 2) When the total root resistance becomes a constant, the absorptive resistance of sunflower occupies 82% of the total resistance, while the conductive resistance of third root 1% and that of secondary root 18%. The absorptive resistance of corn, however, accounts for 99% of the total resistance. 3) The water flow through root vessels can be considered as a Hagen-Poiseulle's flow. The value of the conductive resistance through root vessels of corn is almost equal to the theoretical value obtained by Hagen-Poiseulle's equation. However, as for sunflower, wheat and soybean, the value is 3.5 to 5 times as large as the theoretical value.
