# 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  
Tables 5 and 6 show the results from water extractable concentration for macro and micronutrients. The relevance of each organic residue according to the total amount of water extractable nutrient content is PP > OP > VP > SC > CP > PN > AP, and the elements with greater presence in the total aqueous extract are K > Ca > Mg > Na > Fe > Zn > Mn > Cu, ordered from highest to lowest. The top three soluble nutrients with maximum concentration values are K in PP > K in OP > Ca in PP, and the minimum are Cu in PN > Cu in AP > Cu in CP. What is important from those results is that the rapidly soluble nutrients may contribute to an increase in their concentrations in the soil solution and facilitate the plant absorption and accumulation in plant tissues with a single application on soil [28]. Several studies about nutrient content on organic residues have demonstrated its importance as a nutrient sink and availability for crop yield [11; 12; 13; 14; 55]. The use of these wastes to supply nutrients in a determined growth stage of a plant is one of the possibilities for adequate agricultural management, not only the use of them once during a period of cultivation. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Resolute**} & **Fe (mg kg\({}^{-1}\))** & **Mn (mg kg\({}^{-1}\))** & **Cu (mg kg\({}^{-1}\))** & **Zn (mg kg\({}^{-1}\))** \\ \cline{2-7}  & \(\overline{\textbf{x}}\) & \(\sigma\) & \(\overline{\textbf{x}}\) & \(\sigma\) & \(\overline{\textbf{x}}\) & \(\sigma\) & \(\overline{\textbf{x}}\) & \(\sigma\) \\ \hline AP & 45 b & 7 & 5.7 b & 0.9 & 4.0 a & 0.3 & 4.6 a & 1.7 \\ \hline CP & 377 a & 20 & 38.9 c & 0.5 & 11.2 a & 1.4 & 5.3 a & 0.7 \\ \hline OP & 44 b & 3 & 15.0 d & 1.6 & 4.9 a & 0.3 & 12.4 b & 0.6 \\ \hline PN & 371 a & 26 & 19.4 a & 1.8 & 7.0 a & 0.8 & 11.4 ab & 1.0 \\ \hline PP & 88 b & 4 & 32.2 e & 2.7 & 3.8 a & 0.4 & 15.7 bc & 0.9 \\ \hline SC & 18989 c & 127 & 94.4 f & 0.6 & 79.7 b & 14.6 & 249.5 d & 8.4 \\ \hline VP & 44 b & 2 & 22.2 a & 1.3 & 8.2 a & 1.3 & 19.4 c & 1.5 \\ \hline F \({}^{1}\) & 81741 *** & & 1480 *** & & 99 *** & & 2907 *** \\ \hline \end{tabular} \({}^{1}\) F values followed by *** indicate significant differences at \(p=0.001\). By columns, mean values with letters in common are statistically equal to \(p=0.05\).  
\end{table} 
Table 4: Elemental micronutrient composition, average content (\(\overline{\textbf{x}}\)) and standard deviation (\(\sigma\)) for each residue. Comparing the data of total nutrient content regarding soluble nutrient concentration for each residue (Figure 1), it can be observed that there is no direct relation between a higher nutrient concentration in elemental composition with the values of nutrients in aqueous extractions. SC findings are consistent with those of [PERSON] et al. [43], who found a reduction in water-extractable macro and microelements due to composting process. [PERSON] [41] considers that although drying and composting treatments of organic waste generate a stable product, part of the nutrients can be lost, and the substrate obtained after drying can show low nutrient content. Occasionally, OM takes a long time to incorporate them by degradation into the soil profile due to the high content of recalcitrant material, as is the case for PN (lignified matter), which can be close to 60% of the total amount of organic matter and may explain PN results [67]. Extending the discussion, in most of the residues studied, the four nutrients with the highest elemental composition concentration correspond to macronutrients (Na, K, Ca and Mg), as expected, except for PN and SC, where Fe displaces Na (Tables 5 and 6). Related to aqueous extraction, the highest concentrations are obtained by macronutrients too, with K being the majority, not Ca, as in the elemental composition.