FERTILIZER DIFFUSION IN CONTAINER MEDIUM

The process of fertilizer diffusion was examined using KBr and NaBr sa lts placed at the top of columns filled with a container medium at an initial water content of 4.0, 2.5, or 1.0 g . g(-1) (mass of water/mas s of medium). Columns were sealed to create a protected diffusion zone (PDZ) shielding the system from water infiltration and evaporation. B romide and water distributions were determined after 5, 10, 25, and 12 0 days. Using a Fickian diffusion model, effective diffusion coefficie nts calculated for Br- in the medium at 2.5 g . g(-1) ranged from 2.7 to 4.6 x 10(-6) cm(2) . s(-1), which is 3 to 9 times less than the dif fusion coefficient in water alone, Diffusion rates increased with incr easing medium water content. Differences in the hygroscopicity and sol ubility of KBr and NaBr affected the distribution of water and diffusi on rates in the columns, Redistribution of water was driven to a signi ficant degree by vapor-phase transport, caused by large gradients in o smotic potential, and was most apparent at low water content, At high water content, water redistribution was affected by solution density g radients in the system, This significantly complicates the mathematica l modeling of the system, which renders a simple Fickian diffusion mod el of limited predictive value in high and low water content media.