## 4 Conclusions  
In this study, the release of NO3\({}^{-}\) and DOC from Graphene was investigated in comparison with classical soil improvers (Biochar, Compost, and Zeolites) in two different soils, performing multiple batch experiments with different L/S ratios. Graphene addition did not alter the physiochemical parameters of both soils (CS and SS) and its addition did not trigger any NO3\({}^{-}\) increase respect to Control and to other improvers, possibly stimulating denitrification. Biochar increased EC and pH beyond recommended limits for most crops' growth for both soils, but the effect was mitigated by the increase of L/S ratios. Compost addition produced the highest NO3\({}^{-}\) release, although generally below groundwater quality threshold limits. Graphene helped to decrease NO3\({}^{-}\) concentrations in batches with L/S = 5 and L/S = 10 in both soils. This study emphasizes the importance of employing parallel batch tests with different L/S ratios to study the dissolution mechanisms. In fact, statistical differences between NO3\({}^{-}\) and DOC released for the different L/S ratios used were recognized. Moreover, NO3\({}^{-}\) and DOC concentrations were not strictly linked to dilution effects. The significance of this study lies in going beyond a simple experimental set-up with a single L/S ratio in order to provide a sound understanding of NO3\({}^{-}\) and DOC release from the different L/S mixtures. In this way, it was possible to highlight the close relationship among the results and the choice of the L/S ratio. Furthermore, performing the experiments on two different sandy soils (CS and SS) allowed to demonstrate that the effect of the L/S ratio is also manifested (thou with different magnitude) on soils different mineralogical compositions. Field studies remain the most suitable method to understand the real behavior of new materials in the environment.  
Figure 9: DIC, Ca and Mg concentrations in SSE batches with CS (**upper panels**) and SS (**lower panels**) soils at L/S = 5 at the end of the monitoring period. Error bars denote standard deviations calculated on three replicates, while different letters indicate significative statistical differences.  
Laboratory investigations such as the one here presented are informative and cost-effective tools to better design field experiments.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app12126220/s1](https://www.mdpi.com/article/10.3390/app12126220/s1)]([https://www.mdpi.com/article/10.3390/app12126220/s1](https://www.mdpi.com/article/10.3390/app12126220/s1)). Table S1: Isotherm NO\({}_{3}\) graphene.  
Conceptualization, L.A. and N.C.; methodology, L.A. and N.C.; software L.A. and N.C.; validation, M.M. and V.G.A.; formal analysis, L.A.; investigation, L.A. and N.C.; data curation, L.A. and N.C.; writing--original draft preparation, L.A. and N.C.; writing--review and editing, M.M. and V.G.A. All authors have read and agreed to the published version of the manuscript.  
The research activities of L.A. were part of the Environment, Design and Innovation Ph.D. Program funded by the V:ALERE Program (VAnviteLli pEr la RicErca) of the University of Campania \"[PERSON]\".  
Not applicable.  
The authors declare that the materials are available.  
The authors declare no conflict of interest.