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Ammonium Adsorption by a Zeolite in a Static and a Dynamic System¹

ABSTRACT

New types of soil amendments are being considered to reduce the leaching losses of N fertilizers. One such potential soil amendment is clinoptilolite, which is a natural zeolite with ion exchange properties and an affinity for the ammonium ion (NH₄⁺). The objectives of this study were to quantify the adsorption of ammonium (NH₄) by a clinoptilolite in a shaking study (static system) and to measure how effective this zeolite was in increasing NH₄ retention in soil leaching columns (dynamic system). A batch equilibrium shaking test showed that this zeolite adsorbed 4.3 times more NH₄ than the Nunn clay loam (Aridic Argiustoll) soil. When mixed together with the soil and placed in 6.35 cm (i.d.) by 30 cm long columns (dynamic system), the zeolite significantly reduced the leaching of NH₄⁺ only at a relatively high application rate (135 Mg ha^–1). comparison of the two zeolite application methods at the highest zeolite rate (135 Mg ha^–1) showed that banded treatments significantly reduced the leaching of NH₄⁺, compared with treatments where zeolite was homogenously mixed with the entire soil volume. Indications are, however, that large quantities of clinoptilolite would be required to reduce NH₄⁺ leaching in fine-textured soils.

Key Words: clinoptilolite • Langmuir equation • break-through curves

¹ Contribution from the Department of Agronomy, Colorado State University Agric. Exp. Stn., Fort Collins and published as Scientific Series Paper no. 2789. This project was funded in part by Rocky Mountain Energy Company.

² Graduate Research Assistant, Associate Professor, and Professor, Dep. of Agronomy, Colorado State Univ., Fort Collins, CO 80523.

Received for publication November 12, 1982.