## 3 Results and Discussion  
### Characterization of PIMs  
The physical characterization of APNUT and the APV50 matrix, reported in Table 2, showed a weight loss (WL (%)) similar for both formulations due to the evaporation of internal water, decomposition of organic compounds (SCG), and decomposition of carbonates during firing. The firing process therefore also influenced the total porosity (TP (%)) of the material and the water absorption capacity (WA24 (%)) even if nonvitrified PIMs had greater water absorption due to the absence of glass which inhibited the formation of pores, influencing the entrapment of nutrients and water in the core. The pH and EC respected legal limits for use in soils, with a slight increase in pH in the nonvitrified formulation. pH can be influenced by several factors. Spent coffee grounds, for example, have a neutral pH, therefore, it has been added in previous studies to neutralize the pH of PIMs that used other alkaline poring agents, such as biochar [28]. Fertilizer glass (FG), on the other hand, does not appear to affect the pH of PIMs, even though it has an alkaline pH [6]. The results obtained showed that the use of pumice scraps in the matrix instead of clay had a positive effect on the porosity of the granules, with values around 50% for  
Figure 2: Estimated PPFD map under the LED module used for growth experiments, according to the producer’s software at a distance of 75 cm between the pots and the LED module. The active area used for the growth experiments is indicated by the two black rectangles. APV50, increasing the value as compared to the porosity of PIMs consisting only of clay (43%) reported by [PERSON] et al. [13]. This result also affected other properties such as water absorption, which went from 12% [13] to over 20% in pumice/clay PIMs. The desorption capacity of the granules was measured after the absorption test (Figure 3). The progressive weight decrease was due to the release of water during the 24 h. The APV50 stabilized its weight after 8 h, and both samples returned to their initial dry weight, measured before the absorption test, in 24 h, as during this time they completely released the absorbed water. The lower absorption (22%) and desorption of water from APV50 compared to those of APNUT were due to the presence of the FG which, as already demonstrated, reduced the open porosity of the material. From the analysis of the mineralogical phases plotted in Figure 4a,b, the two core formulations showed identical crystalline phases, identifying quartz (SiO\({}_{2}\)) as the main phase. The other three phases, on the other hand, could be attributed to the presence of the nutrients P and K (leucite: KAlSi\({}_{2}\)O\({}_{6}\); sandine: KAlSi\({}_{3}\)O\({}_{8}\); hydroxyapatite: Ca\({}_{5}\)(PO\({}_{4}\))\({}_{3}\)(OH)). APV50 revealed a lower degree of crystallinity than APNUT did, probably due to the addition of the fertilizer glass, which increased the amorphous phase of the material. The characterization of the two core formulations did not show significant differences in terms of physical and chemical properties between vitrified (APV50) and nonvitrified (APNUT). Therefore, both formulations could be used for agronomic applications, respecting the pH and EC limits for use in soils and demonstrating good draining capacity. The nutrients and pumice could potentially replace FG without compromising the final performance of the fertilizer. The use of nonvitrified nutrients can reduce the energy consumption given by the vitrification process, as demonstrated by the analysis of the carbon footprint [29], improving the sustainability of the final product. To confirm the comparable \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & WL (\%) & Bulk Density (g/cm\({}^{3}\)) & True Density (g/cm\({}^{3}\)) & TP (\%) & WA24 (\%) & pH & EC (4S/m) \\ \hline
**APNUT** & 14.46 & 1.146 & 2.6497 & 56.14 & 30.73 & 7.38 & 0.220 \\
**APV50** & 12.76 & 1.260 & 2.6523 & 51.88 & 22.0 & 6.60 & 0.268 \\ \hline \hline \end{tabular}
\end{table}