Among them, clinoptilolite is the most frequent and abundant zeolite in nature, followed, in order, by mordenite > chabazite > phillipsite > erionite [24]. Natural zeolites are often constituents of volcanic tuffs [25], then, referring simply to \"natural zeolite\" when using these products, from a geological perspective, is improper as it should be better substituted by rocks or tuffs rich in zeolite or zeolitite, in case the zeolite content of the rock is greater than 50% [24]. Although less diffused than clinoptilolite, chabazite zeolite (framework type CHA) is particularly attractive for agricultural and industrial applications because of its very higher CEC (3.84 meq g\({}^{-1}\)) [26,27]. A peculiarity of high agronomic interest exhibited by CHA zeolite is the capacity to bind high amounts of NH4\({}^{+}\) with weak hydrogen bonds to the framework, making it easily accessible and hence exploitable by various potential users (e.g., microorganisms or plants) [26]. The tetrahedral framework of CHA is composed of parallel layers of double 6-rings in ABC sequence with cavities of different size (the wider one bonded by eight-membered rings), in which H2O and exchangeable cations are hosted (most frequently Ca, K and Na) [26] (Figure 1). In central Italy, many pyroclastic deposits have been altered to zeolitites, containing mostly Ca-CHA and K-CHA, and phillipsite. Some of the zeolitic units are tens of meters thick and contain up to 80% of zeolites, and are thereby of commercial interest. Until a few years ago, the resulting material obtained from the cutting of bricks for construction and gardening in zeolitic-tuff quarries was considered a byproduct. Recently, this byproduct was tested as a soil amendment in the framework of the EU project ZeoLIFE (LIFE10 ENV/IT/000321) and revalued. Results from a long term (>3 years) field experiment where this CHA-zeolitite was used as a soil amendment highlighted positive effects on soil N cycling, which promoted the possibility to reduce the N inputs and NO3\({}^{-}\) leaching losses while maintaining or even increasing crop yield (depending on crop type) [8,28]. The interest of the scientific and industrial communities in natural zeolites increased exponentially in the last decades. Hundreds of papers and several reviews have been published about their use and effects in agriculture [12; 19; 24; 29; 30; 31]. However, a mechanistic approach has still not been used to describe how soil N processes are influenced by these highly reactive minerals. Various studies hypothesized that zeolites influence nitrification rates [22; 32; 33] after measuring net variations of mineral N concentrations over time. Measuring net rates does not allow discrimination between production and consumption processes and hence are not an adequate tool to address the effective impact on soil N cycling. To address mechanistically the effects of zeolite amendments on soil N cycling, it is hence fundamental to evaluate their influence on gross N transformation rates once applied to the soil. Nitrification consists of a two-step oxidative microbial conversion of first NH4+ to NO2- by ammonia oxidizer archaea (AOA) and bacteria (AOB) and then to NO3- by nitrite-oxidizing bacteria (NOB). Ammonia oxidation is considered to be the rate-limiting step of nitrification and it is catalyzed by bacterial and archaeal ammonium monooxygenase (AMO) encoded by the gene _amoeba_[34]. Nitrification is normally favoured under well-aerated conditions and a good NH4+ supply [35]. Under oxygen limiting conditions, NO3- can be used by several microbes as a terminal electron acceptor and is converted to the gaseous forms N2O and N2 [36]. The complete process involves the enzymes nitrate reductase (Nar), nitrite reductase (Nir), nitric oxide reductase (Nor), and nitrous oxide reductase (Nos) [37]. Depending on the environmental conditions, substantial amounts of the potent greenhouse gas N2O are emitted from soil, unless the whole N2O is converted to N2 by the enzyme N2O reductase encoded by _nosZ_.