Fertilizer Diffusion in Container Medium

Abstract

<jats:p>The process of fertilizer diffusion was examined using KBr and NaBr salts 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<jats:sup>-1</jats:sup> (mass of water/mass of medium). Columns were sealed to create a protected diffusion zone (PDZ) shielding the system from water infiltration and evaporation. Bromide and water distributions were determined after 5, 10, 25, and 120 days. Using a Fickian diffusion model, effective diffusion coefficients calculated for Br- in the medium at 2.5 g·g<jats:sup>-1</jats:sup> ranged from 2.7 to 4.6 × 10<jats:sup>-6</jats:sup> cm<jats:sup>2</jats:sup>·s<jats:sup>-1</jats:sup>, which is 3 to 9 times less than the diffusion coefficient in water alone. Diffusion rates increased with increasing medium water content. Differences in the hygroscopicity and solubility of KBr and NaBr affected the distribution of water and diffusion rates in the columns. Redistribution of water was driven to a significant degree by vapor-phase transport, caused by large gradients in osmotic potential, and was most apparent at low water content. At high water content, water redistribution was affected by solution density gradients in the system. This significantly complicates the mathematical modeling of the system, which renders a simple Fickian diffusion model of limited predictive value in high and low water content media.</jats:p>

Solute and sediment transport at laboratory and field scale: Contributions of J.-Y. Parlange

“…The efficacy of these credible assumptions was borne out in the remarkable demonstration of the model provided by Parlange [1973], which compares well with the data of Scotter and Raats [1970], as shown in Figures 13 and 14. This work laid the foundation for the decades of exploration of these processes, which govern movement of solutes as a function of osmotic coefficient and water in deserts, near granular fertilizer, and at highly contaminated sites [e.g., Kelly et al 1997;Kelly and Selker, 2001;Scotter, 1974;Weisbrod et al, 2000]. It is striking that although these works add applications and influence of chemical characteristic of the salts in question, no significant advancements in the underlying assumptions or mathematical model have been required or developed since the 1973 paper.…”

Suaeda salsa, A Desalinating Companion Plant for Greenhouse Tomato

“…The CIPS (Fig. 1) has been described by Albaho (1998), Blackburn (1992), Briggs and Green (1991), Green et al (1993aGreen et al ( , 1993b, Green and Schneckenburger (1992), and Kelly et al (1997). It is a continuous subirrigation-capillary system in which water movement is plant-driven in response to uptake to support transpiration and growth.…”

“…The plant collar was then installed, and the stem sealant applied so that the fertilizer was shielded from surfaceapplied water and from gravitational and evaporative water-flow pathways. Solubilized fertilizer ions moved by diffusion in accordance with Fick's laws from the top-placed fertilizer reserve and established ion concentration gradients to the plant roots and other areas of lower solute concentration (Blackburn, 1992;Kelly et al, 1997).…”