Abstract
To realize successive soil moisture profiles in the presence of the roots of transpiring. plants, a macroscopic scale model was designed and a pot-experiment was conducted.
The model, assuming a quasi-steady condition of the plants and an isothermal condition, uses a macroscopic extraction term in the one-dimensional soil moisture flow equation.
It describes both moisture removal by the roots and induced moisture movement through the soil. A numerical procedure based on the finite difference solution is used to solve this model.
An experiment was conducted in a phytotron to test the validity of this model, with soybeans (Glyeine max, Merrill) raised in pots packed with Otosibe sandy loam, without the presence of a water table.
Correspondence between experimentally determined and simulated soil moisture profiles was fairly good except under a very dry condition. And the numerical solution indicates that:
(1) Soil moisture profiles are significantly affected by root density, transpiration rate, axial (=conductive) resistance and root tortousity, but negligibly affected by radial (=absorptive) resistance and evaporation rate.
(2) Extraction rate profiles gradually shift their maximum zones downward, decreasing the maxima. But the profiles for extraction rate per unit root length keep their maxima nearly constant.
(3) The water storage rate by Darcian flow is nearly negligible compared with the extraction rate.
