Communications in Soil Science and Plant Analysis, 42:2370–2378, 2011 ISSN: 0010-3624 print / 1532-2416 online DOI: 10.1080/00103624.2011.605495 Clinoptilolite Zeolite Influence on Nitrogen in a Manure-Amended Sandy Agricultural Soil D. D. TARKALSON AND J. A. IPPOLITO U.S. Department of Agriculture–Agricultural Research Service, Northwest Irrigation and Soils Laboratory (NWISRL), Kimberly, Idaho, USA Zeolite minerals may improve nitrogen availability to plants in soil and reduce losses to the environment. A study was conducted to determine the influence of clinoptilolite (CL) on nitrogen (N) mineralization from solid dairy manure (224 kg N ha -1 ) in a sandy soil. Clinoptilolite was added to soil at six rates (0 to 44.8 Mg CL ha -1 ), each sampled during 11 sampling dates over a year. Over time, nitrate (NO 3 )-N increased, ammonium (NH 4 )-N decreased, but total inorganic N increased. Clinoptilolite did not influence the nitrification rates of initial manure NH 4 -N or mineralization of organic N (ON) over time. It is possible that adsorption of manure-derived potassium (K) outcompeted the NH 4 -N for CL exchange sites. The ON concentration was constant up to 84 days and then decreased by approximately 18% over the remaining time of the study across all treatments. Clinoptilolite use in this sandy soil did not alter mineralization of N from dairy manure. Keywords Ammonium, clinoptilolite, mineralization, nitrate, nitrification, nitrogen, zeolite Introduction Nitrogen (N) from manure can be used to optimize and sustain crop production in many agronomic systems, but nitrate-nitrogen (NO 3 -N) derived from manure through mineral- ization is susceptible to leaching and denitrification loss from soils. Nitrogen losses due to leaching and denitrification from agricultural land, especially in sandy soils, are an environ- mental and economic concern (Perrin et al. 1998). Nitrogen loss from irrigated cropland can significantly contribute to nitrate levels in surface and groundwaters and can subse- quently lead to waterway impairment and eutrophication. On a national scale, agriculture accounts for 50% and 60% of impaired lakes and rivers, respectively (U.S. EPA 2006). Thus, preventing offsite nutrient movement and increased crop N utilization is important. Interest has increased in the use of zeolite minerals as a means of increasing N-use efficiency and lessening offsite N movement. Zeolites are naturally occurring aluminosil- icate minerals (Kithome et al. 1998). More than 50 different types of zeolite minerals have been found (Tsitsishvili et al. 1992). Clinoptilolite (CL), one zeolite of interest, is composed of tectosilicates with isomorphous substitution of aluminum (Al +3 ) and silicon (Si +4 ). It has a high cation exchange capacity (CEC; Perrin et al. 1998) because the CL structure consists of layered and interlinked four- and five-tetrahedral rings, between which Received 9 November 2010; accepted 15 March 2011. This article not subject to U.S. copyright laws. Address correspondence to D. D. Tarkalson, USDA-ARS NWISRL, Kimberly, ID 83301. E-mail: david.tarkalson@usda.ars.gov 2370