USING HYDROPHILIC POLYMERS TO CONTROL NUTRIENT RELEASE

Using diverse technological approaches, many types of delivery devices have been used to supply plant nutrients at a controlled rate in the soil. One new approach is the use of hydrophilic polymers as carriers of plant nutrients. These polymers may be generally classified as 1) n atural polymers derived from polysaccharides, 2) semi-synthetic polyme rs (primarily cellulose derivatives), and 3) synthetic polymers. By co ntrolling the reaction conditions when forming the polymers, various d egrees of cross-linking, anionic charge, and cationic charge can be ad ded, thereby changing their effectiveness as fertilizer carriers. When fertilizer-containing solutions are mixed with hydrophilic polymers t o form a ''gel'' prior to application in the soil, the release of solu ble nutrients can be substantially delayed compared with soluble ferti lizer alone. The effectiveness of a specific controlled-release polyme ric system is determined in part by its specific chemical and physical properties, its biodegradation rate, and the fertilizer source used. Addition of some polymers with nutrients has been shown to reduce N an d K leaching from well-drained soils and to increase the plant recover y of added N, P, Fe, and Mn in some circumstances.