## 3 Results and Discussion
### Release of Nutrients  
The chemical and physical properties of fertilizers have been investigated before and after their use in the soil. The results are shown in Table 4. The pH was generally neutral, and it did not change significantly after using the porous coated materials in the soil. Only APV50_BSF had a small increase to alkaline pH. pH analysis of the coated granules also suggested that the application of the organic coating did not affect the initial pH of the core analyzed (Table 2). These values are in the correct range to maximize the availability of nutrients, and the small increase of the pH was positive. This indicates that there was no \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Number of Plants/Pot (Average)** & **TFM (g)** & **TDM (g)** & **LA (mm2)** \\ \hline
**Control** & 4 & 0.719 & 0.063 & 27.950 \\
**APV50_BSF** & 5 & 1.527 & 0.093 & 40.675 \\
**APNUT_BSF** & 4.5 & 1.623 & 0.095 & 42.025 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Germination and growth values obtained growing lettuce in control condition (substrate without fertilizer) and with fertilizer APV and APNUT. Figure 6: Lettuce biomass measured within 21 days of cultivation in pots with fertilizer APV50_BSF and APNUT_BSF and without fertilizer (C). The error bars represent the deviation standard calculated on the values measured. overapplication of nutrients, which would cause soil acidification, and also indicates the potential of coated PIMs to improve pH in acidic soils [30]. The salinity in the granules decreased after use, demonstrating the release of ions into the soil during the test. Salinity is another parameter to be taken into consideration because excessive salinity can cause the plant to lose its ability to absorb nutrients. Despite the small difference, humidity was lower in APV50_BSF, suggesting that the addition of the fertilizer glass reduced the water absorption capacity of the matrix. Higher humidity is preferable, as the swelling ability of the fertilizer helps the soil retain water, allowing plants to grow for longer periods without the need to add water. From a first analysis of the main elements shown in Figure 7, it was possible to notice that after 21 days the amount of considered elements had decreased in PIMs, suggesting that the ions were released into the soil. The percentages of nutrients released showed some differences between APV50_BSF and APNUT_BSF fertilizers. The nitrogen (Figure 7a) present in the coating was released more in the nonvitrified granules with a 77% reduction from the unused fertilizer (APNUT_BSFnew). The release of nitrogen from APV50_BSF was instead 63%. Considering that the coating was the same for the two fertilizers, the different releases could be due to the different core. Indeed, APNUT showed greater porosity and water absorption (Table 2), which could lead to greater water exchange and nutrient release with the surrounding soil. However, the release of assimilable phosphorus, shown in Figure 7b, showed an opposite trend, as it decreased by 85% and 59% for APNUT_BSF and APV50_BSF, respectively. This could be due to the inclusion of phosphorus in the fertilizer glass as a network former, which would hinder its release [13; 31]. Exchangeable potassium (Figure 7c) decreased by 90% in APV50_BSF and by 88% in APNUT_BSF, showing no differences among the two coated PIMs. The release of magnesium in the soil is another important parameter because it makes possible the synthesis of chlorophyll in plant leaves and is involved in some important enzymatic activities [32]. The release of this element was 64% from APNUT_BSF and 79% from APV50_BSF (Figure 7d). The main difference relates to the release of phosphorus and magnesium, suggesting that different PIMs should be used according to different nutritional needs. These data are in agreement with the results obtained from germination and growth tests carried out with lettuce plants. The addition of APNUT_BSF and APV50_BSF seemed to improve both growth and size of the plant throughout the entire growing cycle.