Many soilless root media have limited ability to retain nutrients. Zeolites are minerals that have substantial nutrient buffering capacity and can be precharged with K, and possibly PO4, and combined with soilless media to provide these nutrients during crop production. The zeolite clinoptilolite was precharged with K and PO4 at two rates that were estimated from sorption isotherms to result in equilibrium root medium solution concentrations of P at >1 μg·ml–1 (low rate) and K at 125 μg·ml–1 (high rate). Precharged clinoptilolite was mixed with a 7 sphagnum peat: 3 perlite root medium to comprise 20% (v/v) and evaluated as the sole source of K and PO4 during production of Dendranthema ×grandiflorum (Ramat.) Kitamura `Sunny Mandalay'. Phosphate, K, Na, and pH were determined on unaltered bulk medium solutions collected over the course of the cropping cycle, and foliar analyses were determined on tissue collected at mid- and end of crop. Plants that relied on K release from precharged clinoptilolite at the low and high rates and received a N/P/-K fertilizer produced growth and tissue K concentrations that were not significantly different than the control which received a complete fertilizer. Plants that relied on PO4 release of precharged clinoptilolite did not result in growth or tissue P levels similar to those of the complete control. Phosphate levels in the root medium solution were adequate only during the first month of the cropping cycle, but PO4 release should be taken into consideration when developing a fertilization program using precharged clinoptilolite to provide other nutrients. Using precharged clinoptilolite at the low rate reduced K losses through leaching to 26% of the amount leached from control plants receiving K at 176 mg·L–1 at each watering.
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