# Soluble Elements Released from Organic Wastes to Increase Available Nutrients for Soil and Crops
## 3 Results and Discussion
### Elemental Composition and Soluble Nutrients
#### 3.2.2 Soluble Nutrients and Solubility Index
The presence of all nutrients in aqueous extraction indicates they are in part soluble in water, but to know the degree of solubility with respect to the total amount of nutrient composition, a nutrient solubility index (I\({}_{\text{N}}\)) was calculated (Table 7). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Resolute**} & \multicolumn{2}{c}{**Fe (mg kg\({}^{-1}\))**} & \multicolumn{2}{c}{**Mn (mg kg\({}^{-1}\))**} & \multicolumn{2}{c}{**Cu (mg kg\({}^{-1}\))**} & \multicolumn{2}{c}{**Zn (mg kg\({}^{-1}\))**} \\ \cline{2-9}  & \(\mathbf{\overline{x}}\) & \(\mathbf{\sigma}\) & \(\mathbf{\overline{x}}\) & \(\mathbf{\sigma}\) & \(\mathbf{\overline{x}}\) & \(\mathbf{\sigma}\) & \(\mathbf{\overline{x}}\) & \(\mathbf{\sigma}\) \\ \hline AP & 1.9 a & 0.1 & 0.8 a & 0.1 & 0.240 b & 0.020 & 4.2 a & 0.3 \\ \hline CP & 1.9 a & 0.2 & 5.7 b & 0.3 & 0.091 b & 0.009 & 4.3 a & 0.3 \\ \hline OP & 2.2 a & 0.2 & 3.6 c & 0.2 & 1.144 c & 0.187 & 5.6 b & 0.6 \\ \hline PN & 8.4 b & 0.5 & 2.1 d & 0.2 & 0.437 a & 0.046 & 4.7 a & 0.4 \\ \hline PP & 1.4 a & 0.2 & 21.2 e & 1.1 & 0.819 d & 0.105 & 10.5 c & 0.6 \\ \hline SC & 24.7 c & 1.6 & 0.4 a & 0.1 & 0.522 a & 0.051 & 4.0 a & 0.2 \\ \hline VP & 3.4 d & 0.4 & 5.2 b & 0.3 & 1.116 e & 0.103 & 6.7 d & 0.5 \\ \hline F 1  & 669 *** & 965 *** & 91 *** & \multicolumn{2}{c}{119 ***} \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Water extract micronutrients average content (\(\mathbf{\overline{x}}\)) and standard deviation (\(\mathbf{\sigma}\)) of each residue. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Resolute**} & \multicolumn{2}{c}{**Na (mg kg\({}^{-1}\))**} & \multicolumn{2}{c}{**K (mg kg\({}^{-1}\))**} & \multicolumn{2}{c}{**Ca (mg kg\({}^{-1}\))**} & \multicolumn{2}{c}{**Mg (mg kg\({}^{-1}\))**} \\ \cline{2-9}  & \(\mathbf{\overline{x}}\) & \(\mathbf{\sigma}\) & \(\mathbf{\overline{x}}\) & \(\mathbf{\sigma}\) & \(\mathbf{\overline{x}}\) & \(\mathbf{\sigma}\) & \(\mathbf{\overline{x}}\) & \(\mathbf{\sigma}\) \\ \hline AP & 199 b & 33 & 1163 a & 31 & 353 c & 25 & 208 b & 19 \\ \hline CP & 316 d & 35 & 616 b & 31 & 963 d & 37 & 386 a & 11 \\ \hline OP & 88 a & 7 & 4688 c & 69 & 725 a & 19 & 397 a & 14 \\ \hline PN & 121 a & 4 & 918 d & 38 & 686 a & 16 & 332 c & 11 \\ \hline PP & 791 c & 31 & 4892 e & 69 & 4330 e & 73 & 1662 d & 41 \\ \hline SC & 807 c & 61 & 1468 f & 62 & 755 ab & 39 & 163 e & 18 \\ \hline VP & 141 ab & 22 & 2415 g & 87 & 810 b & 15 & 613 f & 20 \\ \hline F 1  & 368 *** & 3670 *** & 5491 *** & \multicolumn{2}{c}{2379 ***} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Water extract macronutrients average content (\(\mathbf{\overline{x}}\)) and standard deviation (\(\mathbf{\sigma}\)) of each residue. [PERSON] et al. [42] considered chemical composition as the main aspect that determines the rate of decomposition. In the case of water-extractable forms of nutrients prior to decomposition, other factors would be of importance in determining solubility. For instance, the content of recalcitrant materials could be a factor to consider. Notwithstanding, palm leaves are composed of 66.3% cellulose + hemicellulose and 22.53% lignin [81]; PP is the first residue with the highest amount of soluble nutrients in aqueous extraction after SC but the fourth respect to the total content of nutrients (Tables 5 and 6). Therefore, the hydrophilic nature of palm leaf fibers could be a key factor [81]. In _Pinus halepensis_ needles, despite their high recalcitrant content of lignin mentioned above, the decomposition on the soil leads to an increase in extractable K due to its rapid leaching capacity [11; 16; 57]. K, in general, is the nutrient with the second highest concentration in its elemental composition and the first in aqueous extraction (Tables 5 and 6). [PERSON] et al. [16] found that K (apart from N and P) is the one that is taken up in the greatest quantity from the soil solution and is the most important for olive trees due to its high presence in olives.