# Soluble Elements Released from Organic Wastes to Increase Available Nutrients for Soil and Crops
## 3 Results and Discussion  
The data found in the references about the production of the selected organic wastes in other Mediterranean regions provide us with interesting information on the amounts of waste produced. Our findings may be useful for them because European countries are asked to avoid burning pruning residues in 2023, and other countries may follow too. As well as for meeting circular economy.  
Date palm (_Phoenix dactylifera_ L.) is grown mostly in the Middle East and North Africa [47; 48]. In southern Europe, it is also presented in the palm grove of Elche (Alicante, Spain), which is the largest on this continent (507.4 ha) and is recognized as a World Heritage by UNESCO [32]. Each date palm produces between 10-20 leaves and 20 kg of dry leaves per year [49; 50], and despite the variety of ancestral uses of the different parts of a palm tree, the use of leaves as a soil amendment or substrate has not been studied in European soils in depth. However, in Middle Eastern and North African countries, there are references that tested its usefulness as a biofertilizer or substrate after composting [51; 52; 53] and [PERSON] and [PERSON] [49] successfully used whole palm leaves as mulching to recover degraded areas in Kuwait.  
The FAO [54] considers that Spain produced 6,817,770 tons of grapes and 8,137,810 tons of olives in 2020. There is a scarce number of references that deal with the use of a substrate for the harvest benefit of vine pruning, and an example is [PERSON] et al. [40]. In this work carried out by [PERSON] et al. [20], they obtained 42.3 kg of fine pruning residues and 17.9 kg of thick residues per tree, with an average pruning of 10 olive trees (previous pruning was performed three years prior). In the Andalusian region (Spain), olive pruning residues account for between 1.95 and 4.5 million tons per year [21]. Studies have been carried out to verify shredded pruning olive tree residue's contribution to olive groves. [PERSON] et al. [21] concluded that soil benefits more if residues are provided without burning (greater carbon sequestration, increase in organic matter and reduction of erosion). [PERSON] et al. [16] state that the use of olive tree pruning is a sustainable practice to improve plant nutrition.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Parameter** & **Na** & **K** & **Ca** & **Mg** & **Fe** & **Mn** & **Cu** & **Zn** \\ \hline Wavelength (nm) & 589.0 & 766.5 & 422.7 & 285.2 & 248.3 & 279.5 & 324.8 & 213.9 \\ \hline Bandpass (nm) & 0.5 & 0.5 & 0.5 & 0.5 & 0.2 & 0.2 & 0.5 & 0.5 \\ \hline Lamp current (mA) & max. 8 & max. 8 & max. 10 & max. 4 & max. 15 & max. 12 & max. 5 & max. 10 \\ \hline Atomization mode & \multicolumn{4}{c}{emission} & \multicolumn{4}{c}{absorption} \\ \hline Flame type & \multicolumn{4}{c}{air/acetylene} \\ \hline Fuel flow rate (l min\({}^{-1}\)) & 1.1 & 1.1 & 1.4 & 1.1 & 0.9 & 1.0 & 1.1 & 1.2 \\ \hline Detection limits (mg l\({}^{-1}\)) & 0.005 & 0.010 & 0.08 & 0.005 & 0.06 & 0.03 & 0.04 & 0.01 \\ \hline \end{tabular}
\end{table}
Table 1: AAS instrumental parameters.  
In 2020, more than 4 million tons of almonds with shells were produced worldwide [54], with Spain being the second largest producer. This means that almond pruning is available in many areas as a soil amendment. _Pinus halepensis_ is widely distributed in Mediterranean climate areas, and needle fall production measured in Spain was between 2080 and 2218 kg ha\({}^{-1}\) year\({}^{-1}\)[55]. We have found various references that prove that needle fall contribution to soil nutrition has been carried out previously [55; 56; 57]. Sewage sludge is a by-product obtained from the treatment of urban wastewater. In Spain, around 1,200,000 dry matter tons are produced annually, mainly used for agricultural purposes (80%) due to their high nutrient content [58]. Sludges require stabilizing treatments to reduce water content and pathogens and to ensure organic matter stability; composing is one of the most applied processes.