NUTRIENT TRANSPORT INSIDE AND OUTSIDE THE ROOT RHIZOSPHERE

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Abstract
An earlier article briefly reviewed the possible effects of the rhizosphere on nutrient transport to a root; transport in the rhizosphere was considered separately from bulk transport with coupling arising from the rhizosphere bulk-soil boundary conditions. Four linear nutrient transport problems were considered and solved analytically. In this article the results of the earlier article were extended to account for nonlinear root boundary conditions; arbitrary spatial and temporal changes in the buffer power and diffusion coefficients; nonlinear sources and sinks of nutrient in both the rhizosphere and bulk soil; and arbitrary, nonlinear, initial conditions. The computer results indicate that if the buffer power, effective diffusion coefficients, and sources or sinks differ between the rhizosphere and bulk soil, an alteration of the concentration profile and total nutrient uptake may take place. This effect can play a role in plant shoot development, as such development is directly affected by nutrient uptake. The numerical model was calibrated with the analytical solutions to the linear problems presented in Cushman (1982). Although the analytical solutions agree with the numerical solutions, it is much less time consuming and expensive to use the numerical simulation. The numerical solution is much more general than the analytical solution. If the diffusion coefficient, buffer power and source of sink are determined as a function of moisture content, the numerical model can handle transient-state moisture conditions provided the moisture content does not change too rapidly. Such data at this point, however, are not available.

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