Using saturated or enriched zeolites as slow release fertilizers (SRFs) is considered as an environmental-friendly strategy to enhance use of macronutrients in sandy soils. In this paper, two natural zeolites, clinoptilolite (CLI) and chabazite (CHA) were used as mineral precursors to prepare NH4+/K+ saturated clinoptilolite (NH4+/K+-CLI) and chabazite (NH4+/K+-CHA) as zeolitic nutrient sources (ZNSs). Comparison between the nutrient retention capabilities of these ZNSs was one of the main objectives of this study. The NH4+/K+-CLI and NH4+/K+-CHA were prepared by soaking the zeolites in NH4Cl and KCl solutions, respectively. Leaching tests were performed on a sandy soil amended with chemical fertilizers (CFs), NH4+/K+-CLI and NH4+/K+-CHA to evaluate the leaching properties of them. The results indicated that approximately 84% and 88% of the NH4+ and K+ of soils fertilized with CFs were lost during the experiment, respectively. While, the NH4+ and K+ losses from soils amended with NH4+/K+-CLI and NH4+/K+-CHA were 29%, 23%, and 14%, 24%, respectively. Despite of drastic changes in leaching behavior of CFs, nutrient losses from ZNSs were more uniform during the experiments. No significant difference was found between the two studied zeolites on reduction of K+ loss. However, CHA was more effective in preventing NH4+ loss during leaching.

The search for safer and sustainable management of animal manure is a global and topical challenge, in particular for the reduction of nitrogen (N) content. The use of natural adsorbents as zeolite-rich tuffs is recognized as a valid method to recover N, in the form of ammonium (NH₄⁺), from animal manure. While the scientific literature is rich in studies performed on synthetic solutions and using clinoptilolite zeolites as adsorbent, it lacks information concerning adsorption in real liquid manure and using other types of zeolite-rich tuffs (e.g., chabazite). This work aims at exploring the NH₄⁺ adsorption process from raw liquid swine manure, using a chabazite-rich zeolite tuff as adsorbent. The effects of temperature, contact time, and grain size have been assessed. Isotherms, kinetic models, and thermodynamic parameters have been investigated. Harkins-Jura isotherm correlates well with the observed data, in accordance with the formation of an adsorption multilayer. Kinetic data have been explained by intraparticle diffusion and pseudo-second-order models. In conclusion, the natural chabazite tuff has proven to be a valid material for NH₄⁺ adsorption from raw liquid swine manure. In particular, to reach the highest adsorption capacities and adsorption rates, it is recommended to use it at a fine particle size and with dosages < 6 %.

The application of natural zeolites to improve soil quality and functioning has become highly popular, but we still miss information about the long-term effects on the soil due to its application. This study assesses the soil quality index (SQI) of three distinct agricultural soil systems 6-10 years after a single application of natural chabazite zeolite as a soil amendment. These soils exhibit different management practices: intensive arable (cereals), intensive perennial (pear) and organic perennial (olive). In the arable system, a zeolite application dosage of 5, 10 and 15 kg m^-2 was tested and compared to unamended soil. In the two perennial systems, an application of 5 kg m^-2 was tested against untreated reference sols. A set of 25 soil physical, chemical and biological parameters linked to soil health and quality were analysed at each experimental site. The dataset was investigated through Principal Component Analysis (PCA) to calculate the soil quality index (SQI) using linear scoring. In the arable-cereal field, the SQI doubled (0.3 to ca. 0.6 for all amendments) in chabazite-amended plots; a dose effect was not recognizable. In both perennial fields, the SQI was significantly higher in the chabazite-amended plots (5 kg m^-2) with similar increases as compared to the arable-cereal field. At each site, the indicators selected by the PCA were different, indicating that chabazite addition impacted soil quality differently in each cropping system. Overall, the results highlighted a significant increase in soil quality with chabazite amendment, which confirms its potential for increasing soil health in the long-term.