The Impact of Nanophase Iron-Oxide Coated Clinoptilotite Zeolite On Nutrient Retention in a Sand-Based Root Zone Mix.

Sand-based growing media have low cation exchange capacities and therefore lack the capacity to retain nutrients in the root zone.  Natural clinoptilotite zeolites coated with nanophase iron oxide adsorb both cations and anions, so mixing them into a sand-based growing medium may enhance nutrient retention and reduce leaching losses. The objective of this study was to investigate the influence of nanophase iron-oxide coated natural zeolite (NPNZ) on nutrient retention in a sand-based growing medium.  NPNZ was fertilized with 1.7 g/kg 15-30-15 soluble fertilizer and mixed with USGA grade sand at 0, 5, 10 and 20% (w/w). Three replications of each mix were packed in 25.5 L lysimeters in a green house and grown in Crenshaw bentgrass. The columns were irrigated every two to three days, allowed to drain for 24 hours and the leachate collected to determine volume, pH, EC, and major nutrients. The treatments received equal cumulative amounts of fertilizer (15-30-15) over four subsequent applications but in different proportions during each application. Grass in each treatment was periodically clipped to determine yield and tissue concentrations of P and N. Results indicate that urea is poorly retained by the NPNZ-sand mix because of its neutral charge. The presence of urea and other nutrients in leachate caused increases in pH and EC suggesting that urea fertilizers are a poor choice for sand-based root zone mixes.  In contrast P and NH₄-N were largely retained by NPNZ in the root zone mix. Initial grass yield and tissue concentrations of P and N were negatively correlated to the level of NPNZ in the root zone mix suggesting that there is a optimum level of NPNZ and fertilization that will protect nutrients from leaching yet also provide an adequate reservoir of plant available nutrients.