Revitalizing rainfed certified olive groves through the application of organic amendments and beneficial fungal consortia

Agricultural soils in the Mediterranean basin face a critical state of degradation, characterized by the depletion of organic matter and a high dependence on external inputs. Faced with this scenario, and the urgent need for practices to guarantee economic and environmental viability, the RESIOLIVA Operational Group and the RES2SOIL project propose an agroecological and circular management. The main objective is to safeguard the sustainability of certified olive groves and increase their adaptive capacity to climate stress.

A field trial was established in La Campana (Seville, Spain) to monitor 3,169 certified olive trees (cv. Sikitita-2 and Arbosana). A factorial experimental design was used to evaluate six treatment combinations across replicated plots, testing (i) the application of green compost + biochar produced from olive pomace and (ii) inoculation with beneficial Trichoderma spp. with plant growth–promoting activity, both individually and in combination. In addition, the influence of prior mycorrhization of the planting material was assessed.

The monitoring strategy combined soil physicochemical properties, elemental composition, water retention capacity, thermogravimetric analysis, and infrared spectroscopy with measurements of biological activity, as well as plant physiological assessments based on photosynthetic yield and chlorophyll content. Preliminary results showed that the organic-amended plots had statistically significant increases in soil organic carbon, mainly stable fraction, supporting its role as a carbon sink, while most of the physicochemical parameters remained stable. Besides, amended plots consistently maintained higher soil moisture levels at 0-20 cm depths. However, the trial was severely disrupted by extreme floodingin February 2025, accumulated rainfall exceeded 600 mm, causing prolonged waterlogging and anaerobic conditions and leading to higher-than-expected plant mortality, which reduced the statistical robustness of the first vegetative cycle, resulting in lower survival rates compared to controls. Notably, the rainfed-bread Sikitita proved highly susceptible to root asphyxia, whereas the irrigation-adapted Arbosana showed superior tolerance to high precipitation rates. Monitoring continues to assess amendment stability, C dynamics, and soil structural interactions, providing key information for designing rainfed scenarios.

ACKNOWLEDGEMENTS
The Resioliva Operational Group (GOPO-CO-23-0004) gratefully acknowledges funding from the European Agricultural Fund for Rural Development (FEADER) and the Regional Government of Andalusia through the Ministry of Agriculture, Fisheries, Water and Rural Development, in accordance with Article 18.4 of Law 38/2003 of November 17 (https://agriculture.ec.europa.eu/index_es).
This work was funded by the RES2SOIL project (PID2021-126349OB-C22) of the MCIN/AEI/10.13039/501100011033.