The abundance of the functional gene  
Figure 1: Conceptual scheme of the experiment, including the main expected results for each treatment. Representation of framework structure and location of water molecules and extra-framework cations of the chabazite zeolite were taken and adapted from [26]. _amoA_ and the genes _nitS_ and _nosZ_ can give indications on the efficiency of the respective processes [38; 39; 40; 41]. CHA zeolite can be also utilized for removing NH4\({}^{+}\) from wastewaters, including those that originated from livestock [42; 43]. These \"charged\" zeolites, which have adsorbed consistent amounts of NH4\({}^{+}\), can be eventually exploited as \"slow-release\" fertilizers to recycle the adsorbed N efficiently [28]. NH4\({}^{+}\)-charged zeolites have been found to increase NO3\({}^{-}\) concentrations over time when used in soil or as cultivation substrate [10; 44; 45]. In this view, the use of a synthetic nitrification inhibitor (NI) may represent a valid countermeasure. NIs are effective synthetic substances used for promoting NUE and reducing N losses by slowing nitrification [46]. NIs facilitate the retention of soil N in the form of NH4\({}^{+}\) by inhibiting the AMO through random binding to the membrane-bound enzyme. AMO shows a broad substrate range [47], and NIs compete with NH4\({}^{+}\) for the active site of this enzyme, causing a delay in the first and rate-limiting step of nitrification [48]. Within commercially available NIs, dicyandiamide (DCD) and 3_A_-dimethylpyrazole phosphate (DMPP) are the most widely used [49] but DMPP was found to have higher efficiency at lower application rates (10 times less than DCD) [50; 51]. Although DMPP capacity to reduce nitrification rates and N2O emissions has been well established [52; 53; 54], the effects on soil N gross rates (especially ammonification rates) have been poorly investigated as well as the combined effects with natural zeolites in soil. One of the few examples is [55], where a general increase of mineralization of recalcitrant organic N after DMPP addition in two soils was observed, beside a reduction in gross nitrification and N2O emissions. DMPP as an organic molecule can decompose and hence provide a source of C for microorganisms that may further stimulate mineralization processes. The soil organic C content and amount of clay minerals can also play a role in the performance of DMPP as a consequence of sorption-effects [56]. High sorption of DMPP may result in a lower availability to microorganisms and hence to a lower efficiency; the authors of [55; 57; 58] evaluated the effects of natural and NH4\({}^{+}\)-charged CHA-zeolite on the sorption of DMPP in soil and concluded that the soil was more efficient in binding DMPP, thanks to the presence of higher levels of organic C that favored the sorption of DMPP. The CHA-zeolite contained in the tuff could not, therefore, retain DMPP by ion exchange processes but instead brought mostly to a reduction in the overall sorption capacity of the soil, due to their lack of organic C. This outcome speculates if this lower sorption capacity in zeolite amended soils also affects the availability of DMPP to soil microbial biomass and consequently the overall efficiency in inhibiting nitrification. This is the first study to our knowledge that investigates the effects of zeolite-tuff on gross ammonification and nitrification rates. We tested natural and NH4\({}^{+}\) charged CHA zeolite-tuff with and without the addition of DMPP in short-term incubation (24 h) (Figure 1). We aimed to address the following research questions (_RQ_) and hypotheses (_Hy_):  
_RQ 1:_ Does the addition of CHA in natural or NH4\({}^{+}\)-charged state to soil have any effects on gross N mineralization and nitrification rates? _RQ 2:_ Is the performance of DMPP improved by the presence of natural or NH4\({}^{+}\)-charged zeolitite?