COMPUTER-GENERATED TIME AND DISTANCE OF NUTRIENT CONCENTRATIONS UNDER PURE DIFFUSION CONDITIONS WITH APPLICATION TO TIMED-RELEASE CAPSULES

The refractive index change caused by KCl diffusing from a cylinder into agar gel was found to distort a grid projected through it by laser light. By ray tracing and Fermat’s Principle it was shown that values of concentration of KCl at various times and distances were within experimental error of those calculated from the transient diffusion equation for diffusion from a cylindrical source. The diffusion equation was derived for the first time using Eyres’ method. Since the model and mechanism were confirmed as correct by experiment it was then possible to design a computer program to predict transient concentration gradients and hence concentration at any distance and time. The program has built into it flexibility to deal with such expected variables in soil as tortuosity, water content, etc., as well as different diffusion coefficients for different nutrients and also multiple sources. Such a program should be very valuable to fertilizer suppliers in designing timed release capsules and to those using...