CLINOPTILOLITE ZEOLITE: EFFECT ON AMMONIUM EXCHANGE REACTIONS, NITRIFICATION AND PLANT NITROGEN-USE EFFICIENCY.
AuthorFerguson, Gregory Alexander
AdvisorPepper, Ian L.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractClinoptilolite zeolite has a theoretical cation exchange capacity of 2.25 moles of charge kg⁻¹, and a rigid three-dimensional lattice riddled with angstrom-sized tunnels, and interconnected voids, in which water and exchangable cations are held. The hypothesis was that clinoptilolite had the facility to preferentially and internally sorb NH₄⁺, where it would be physically protected from microbial nitrification. Hence nitrification rates would be decreased and plant N-fertilizer use efficiency increased. Exchange capacities of clinoptilolite determined at 30°C by saturation/desorption for NH₄⁺, K⁺ and Na⁺ were approximately 2.00 moles of charge kg⁻¹, while capacities for Ca²⁺ and Mg²⁺ were 1.53 and 0.97 respectively. On this basis three site groups were identified: those accessible to all cations studied, sites accessible to all cations but Mg²⁺ and sites only accessible to NH₄⁺, K⁺ and Na⁺. Equilibrium isotherms were used to determine selectivity of site groups at 30°C. Consideration of site accessibilities and selectivities indicate an overall preference of clinoptilolite of: K⁺ > NH₄⁺ > Na⁺ = Ca²⁺ > Mg²⁺. Notably, the plant macronutrient cations, K⁺ and NH₄⁺, are preferentially sorbed. Nitrification of NH₄⁺ on clinoptilolite amended sands incubated at 20% volumetric moisture capacities, was studied in the laboratory. Treatments were washed mortar sand amended with 0, 5 and 10% clinoptilolite by volume and 2.38 and 3.57 moles of NH₄⁺ m⁻³ of sand-clinoptilolite mix. Nitrification was evaluated by monitoring NH₄⁺ loss. Rates of nitrification decreased with increasing clinoptilolite amendment and decreased with N-fertilizer initially applied. The effect of clinoptilolite in slowing nitrification was more pronounced at higher initial NH₄⁺-fertilizer application. The hypothesis that internally sorbed NH₄⁺ in clinoptilolite is physically protected from microbes resulting in decreased nitrification rates was confirmed. The effect of clinoptilolite on N-use efficiency of creeping bentgrass was studied in a field trial. Factorial treatments included washed mortar sand amended with 0, 5 and 10% clinoptilolite by volume and 25, 50 and 75 kg of N ha⁻¹ growing month⁻¹. Approximately 45% of applied N was harvested in clippings from 10% clinoptilolite amended sand in contrast to 36% N recovery on 100 % sand. This supports the hypothesis of improved plant N-fertilizer use efficiency on clinoptilolite amended sand.
Degree ProgramSoil, Water and Engineering