Retention and transport of nitrate and ammonium in loamy sand amended with clinoptilolite zeolite

Agricultural soils of southern New Mexico, especially sand and sandy loams receiving numerous nitrogen (N) fertilizations, are prone to leaching large amounts of N to shallow groundwater. Adsorption and leaching experiments were conducted to investigate the use of clinoptilolite zeolite (CZ) as an amendment to sandy soils to increase N retention and reduce nitrate (NO₃^- ) leaching. Urea-ammonium-nitrate (UAN 32) fertilizer was applied to four soil treatments to simulate crop irrigation. The treatments were composed of 100% CZ, 100% loamy sand (LS), a mixture of 80:20% (LS:CZ), and a mixture 60:40% (LS:CZ) by mass, respectively. Results from the experiments showed an inverse relationship between nitrate-nitrogen (NO₃^- -N) adsorption and the amount of CZ added to soil caused by anion exclusion and a direct relationship between ammonium-nitrogen (NH₄⁺-N) adsorption and the amount of CZ mixed with LS due to NH₄⁺-N entrapment by the CZ molecules. It is therefore recommended to use other types of fertilizers that do not include NO₃^- to LS soils amended with CZ in order to reduce the risk of leaching. Otherwise, it is suggested to apply fertilizers containing ammonium nitrate in LS soils amended with CZ at reduced rates but at higher frequencies to meet plant demands.