## 5 Conclusions  
The outcomes of this study represent a starting point for a mechanistic understanding of the effects of natural and NH\({}_{4}\)-enriched CHA-zeolites (used in the form of zeolite tuff) on the short-term soil N cycle, also in combination with DMPP as a nitrification inhibitor. A visual summary of the obtained results is represented in Figure 5. This study highlighted that CHA-zeolite in natural state did not alter considerably short-term gross ammonification but instead slightly reduced nitrate production rates under these specific experimental conditions. However, if CHA zeolite-tuffs are applied at the field-scale, even a short delay  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{3}{*}{**Treatment**} & \multicolumn{2}{c}{**N Input**} & \multicolumn{2}{c}{**N\({}_{2}\)O-N/N**} & \multicolumn{1}{c}{**\({}^{\dagger}\) DMPP**} & \multicolumn{1}{c}{\({}^{\dagger}\)\(\mathbf{\mathbf{\SIUnitSymbolMicro\textunders  
of the nitrification process can be of great agronomic and environmental interest. The addition of NH4-enriched zeolites improved ammonification but not gross nitrification in the short-term period, indicating that probably other non-targeted N processes were stimulated (i.e., nitrifier-denitrification). The addition of CHA in natural state has not altered the performance of DMPP, while the presence of NH4+-charged CHA led to a stronger inhibition effect of DMPP and potentially stimulated other non-targeted N processes such as DNRA. These different effects on the N cycle observed in the soil amended with NH4+-charged zeolites are thus not attributable to a zeolite-effect but more likely to the additional N (and C) source introduced with this amendment. We thus suggest taking into consideration the use of DMPP or other nitrification inhibitors when using NH4+-charged zeolites as a soil amendment or fertilizer. Further experiments are required for enlarging the dataset to also evaluate the effects of other typologies of zeolites (e.g., clinoptiolite), other soil textures (e.g., sandy soils), longer incubation times, and other important variables such as temperature, moisture, and presence of crops. Given the results obtained in this experiment, particular emphasis should be dedicated in future studies to unveiling the effects of natural and NH4-enriched zeolite on long-term soil gross N rates. **Supplementary Materials:** The following are available online at [[https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)]([https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)) 7/11/6/2605/s1. Table S1: Primers used for quantitative PCR. Table S2: Quantitative PCR thermal profiles for the different target genes. **Author Contributions:** Conceptualization, K.M.K. and G.F.; formal analysis, G.F., E.D. and G.G. ; funding acquisition, G.F. and K.M.K. ; methodology, G.F. and K.M.K. ; investigation, G.F., K.M.K., E.D., G.G., M.G., J.F., and A.M.; resources, B.F., M.G., and K.M.K. ; supervision, K.M.K., G.F., M.C., S.Z.-B., and M.G. ; validation, M.G., E.D., and G.F.; visualization, G.F., E.D., and K.M.K. ; writing--original draft, G.F.; writing--review and editing, K.M.K., E.D., and M.G. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was sustained by the University of Ferrara (UNIFE) with the PhD Fellowship of [PERSON] and IUSS mobility grant 2016. Open access funding was provided by BOKU Vienna Open Access Publishing Fund. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Data is contained within the article and supplementary material. Figure 5: Summary of the main results. “=” symbols indicate no observed variations, arrows indicate an increase or decrease in the parameter. Question mark next to processes depicts a potential pathway that is supported by the data, but not directly measured, and hence the necessity to acquire more data. NZ treatment is the soil amended with 10% of CHA zeolite-tuff in natural state, while CZ is soil amended with 10% CHA zeolite-tuff enriched with NH4+.