Use of Ion Exchange Membranes as Root Simulators to Assess Nutrient Ion Supply Rates in Soils
Schoenau, J.J. and P. Qian. 2007. Proceedings of 2007 Dahlia Greidinger Symposium: Advanced Technologies for Monitoring Nutrient and Water Availability to Plants, March 12-13, Technion University, Haifa, Israel
Abstract
Ion exchange resins in membrane form may be regarded as rudimentary plant root simulators when
placed in direct contact with soils and sediments. Anion and cation exchange membranes act as
ion sinks or dynamic exchangers when placed directly into contact with the medium. Nutrient ions in
soil solution and on soil colloids will exchange with counter ions on the membrane surface and
become adsorbed. The measurement of ions adsorbed on the surface of the membrane after a
specific period of contact time is used to provide an indication of potential ion supply rate, with units
of weight of nutrient ion adsorbed per unit surfacearea of membrane over the contact time.
Encapsulation of the membranes into probes (Plant Root Simulator Probes™) allows the direct
insertion of membranes into intact soils in laboratory, greenhouse or field. The ion supply rate
measured in this manner is highly sensitive to ion concentration in solution, diffusive conditions and
sorption-desorption, mineralization-immobilization processes as they are affected by soil and
environment. Several examples are covered of the successful use of ion exchange membranes to
study the impacts of management on nutrient availability. Applications dealt with include evaluating
the effect of different crop residues, amendments, fertilization and tillage practices on available
nitrogen and phosphorus supplies in the soil. The sensitivity of the technique to biological and
physico-chemical processes that are operative the soil environment such as mineralization-immobilization and diffusion is an advantage in mimicking what a plant root would experience.
