“Alperujo” and leaves as amendments: their effects on the uptake of essential and non-essential elements in olive groves in Southern Spain

In Spain, the approval of Law 7/2022 (Art. 4.1), together with Royal Decree 506/2013 and its subsequent amendments (Royal Decree 999/2017), has led to the reclassification of “alperujo” as a fertilizer for agricultural use. As a result, it is no longer considered a waste but rather as a by-product. Con-sidering the global promotion of the circular economy and the issues related to soil erosion and degradation in olive groves, using “alperujo” and leaves as soil amendments has been deemed a potential solution to address both problems. “Alperujo” is an oily paste that contains pulp residues, small fragments of olive pits, and still retains certain amounts of nutrients and trace metals. Essential and non-essential nutrients can be added to the soil and then transported to different parts of the olive tree. Furthermore, olive oil is a key product in the Mediterranean diet, making it crucial to ensure its suitability for consumption and the absence of risks to human health. The study was carried out in unirrigated traditional olive grove, located in Tor-redelcampo-Jaén (Spain) and the aim was to evaluate the essential and non-essential elements contents in branches, leaves, and olives and in the soil surface (0-20 cm) under different land management practices: (1) conven-tional tillage (CT); (2) CT plus the addition of “alperujo” (A) (270 Mg ha-1y-1); (3) CT plus the addition of olive leaves (H) (270 Mg ha-1y-1). The ele-ments assays were conducted using an atomic adsorption spectrometry (SpectrAA 20 Varian) via graphite furnace and flame after samples minerali-zation. This study showed that, in general, the treatments applied to plots (H) and (A) proved to be beneficial both for the soil and for the olives. The results were especially satisfactory in the soil of the plot (H); the leaves are a more easily degradable material than the alperujo. The results obtained have shown the translocation of nutrients from the soil to the branches, leaves, and olives. In addition, the concentrations of non-essential nutri-ents found in the olives were compared with the critical values given in the [1] and they were lower than the critical values, therefore the treatments ap-plied do not endanger human health.