Today’s agriculture has the challenge of ensuring food supply for a growing population while human activity has already deteriorated about 40% of the world’s soils, reducing productive capacity and increasing reliance on mineral fertilizers. In this context, valorizing and recycling mineral and agricultural waste for use as substrates or soil supplements enhance a sustainable economy, as well as the development of activities focused on finishing the soil nutrients’ cycle. Looking for an effective solution to the massive waste generation and to enhance the agronomic qualities of soils, this study investigates the agronomic impact of contrasting inorganic and organic materials such as green compost (GC), wood biochar (WB), rice husk ash (RA), and volcanic ash (VA) as amendments to an alkaline Luvisol under controlled conditions. In this sense, barley seeds were planted and grown in a greenhouse under controlled conditions for 60 days on a soil amended with the aforementioned materials. The amendments demonstrated appropriate attributes for improving soil agronomic properties, enhancing the soil’s nutritional content with no effect on barley germination. The WB showed high aromaticity and abundance of refractory organic C. Both ash-rich amendments showed high P and K contents, which are important elements for plant development. The GC has high water retention capacity and an adequate C and N balance. Although the application of the amendments had no effect on barley yields, the plants from the ash-amended pots showed an increase of Photosystem II efficiency, indicative of a better physiological status. In terms of toxicological safety, the abundance of trace elements in soils and plants was investigated. All soils met the maximum allowable limits for these persistent pollutants. Nevertheless, longer-term tests on plants are required to determine the risk of Pb accumulation, particularly in soils amended with GC and compost-ash mixtures. The simultaneous combination of organic and inorganic amendments showed adequate agronomic attributes. WB analysis revealed its great recalcitrance and carbon sequestration potential.

The application of organic amendments, both traditionally utilized (e.g., compost) and more recent innovations (e.g., biochar), to degraded agricultural soils is being driven by international initiatives in the current context of global change, such as the "4 per mil initiative". The main goal is to achieve sustainable soil quality restoration, contributing to carbon (C) sequestration, while also providing a practical use and value addition to agro waste products. Despite the generally recognized benefits of such applications on soil productivity and physical properties [1,2], their effects on soil C cycling and sequestration are not as comprehensively understood. Results exhibit considerable variability depending on the type of amendment and the specific soil, emphasizing the need for a more in-depth investigation in this area [3]. Therefore, the aim of this study was to analyze the effects of contrasting organic amendments on soil carbon stability.To accomplish this, two soils commonly employed in humid grasslands of the northern region and rainfed agriculture in the southern region of the Iberian Peninsula, respectively, were amended in triplicate at 10% (w/w) with wastewater sludge biochar, olive pomace biochar , white poplar wood biochar, rice husk biochar, cow manure digestate, a mixture of cattle manure and straw digestate (CM&SD), green compost (GC), and a mix of GC and OPB. A control was also established for each type of soil. After inoculating all the vessels with 1 mL of a standard microbial solution, respiration rates (CO2 emissions) were measured every 6 h over 100 days using an automated respirometer (Nordgren Innovations, Sweden) under controlled conditions (25°C; 60% water holding capacity). The data obtained were plotted against the incubation time by an exponential curve to discern the C stability through fast and slow C pools.Our findings revealed significantly enhanced stability of recalcitrant carbon (slow C pool) in both soils treated with biochars, particularly in the case of RHB and WB. These amendments substantially extended the mean residence time of the slow C pool (MRT2) by a factor of six to nine. The overall trend observed for the studied amendments was as follows: biochar >> green compost >> digestates > native soil carbon. In contrast, the alkaline rainfed soil exhibited a faster carbon turnover rate compared to the grassland soil, resulting in a lower C MRT2.Acknowledgements: The Spanish Ministry of Science and Innovation (MCIN) and AEI are thanked for funding the project RES2SOIL (PID2021-126349OB-C22). The European Joint programme EJP SOIL from the EU Horizon 2020 R&I programme is thanked for funding the subproject EOM4SOIL (Grant agreement Nº 862695).References:[1] De la Rosa, J.M., Pérez-Dalí, S.M., Campos, P., Sánchez-Martín, Á., González-Pérez, J.A., Miller, A.Z., 2023. Agronomy, 13, 1097.[2] Doblas-Rodrigo, A., Gallejones, P, Artetxe, A., Merino, P., 2023. Sci. Total Environ., 901, 165931.[3] De la Rosa, J.M., Rosado, M., Paneque, M., Miller, A.Z., Knicker, H., 2018. Sci. Total Environ., 613-614, 969-976.

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.ACKNOWLEDGEMENTSThe 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.

The management of dredged riverine sediments represents a significant environmental challenge due to the massive volumes generated annually [1]. Reusing these sediments as agricultural amendments offers a promising opportunity to improve crop yields and plant quality [2]. In the Guadalquivir marshlands (Seville, Spain), soils also face severe physical constraints due to their clay-rich texture and low soil organic carbon content. In this context, targeted organic amendments, such as plant-based composts, are proposed to enhance nutrient availability and overall functionality in formulated Technosols.Within this context, a six-month field trial was established in a fine-textured soil near the Guadalquivir River, characterized by compaction and poor drainage, under the framework of the SARECO Project, which formulated Technosols through the co-application of two riverine dredged sediments from the Guadalquivir River (supplied by the Port of Seville) and green compost, mixed with the native soil, as a strategy to restore soil health. Winter wheat was cultivated, and over the six-month period (until harvest) we monitored soil physical properties, organic matter composition and respiration rates, carbon dynamics, and crop productivity.The results showed that the Technosols significantly improved soil physical properties, with lower soil bulk density and penetration resistance. These improvements were accompanied by sustained organic carbon enrichment throughout the trial. Soil respiration rates increased initially in the Technosols but declined over time. The combined application of sediments and compost produced a synergistic effect on yield, exceeding the control in grain weight and grains per head, while total biomass and protein content remained comparable to the control soil.Overall, these findings confirm that combining riverine dredged sediments with organic amendments in fine-textured, carbon-poor soils is a sustainable strategy that increases soil organic carbon stocks while maintaining competitive crop yields. This approach provides a viable pathway for dredged-sediment valorization and the restoration of degraded agricultural soils.REFERENCES [1] Renella, G. Sustainability (2021), 13(4),1648.[2] De la Rosa, J. M., Pérez-Dalí, S. M., Campos, P., Sánchez-Martín, Á., González-Pérez, J. A., & Miller, A. Z. Agronomy (2023), 13(4), 1097.ACKNOWLEDGEMENTS: Authors gratefully acknowledge CSIC for funding the SARECO project (COCRE24015; CSIC COCREA 2024 – circular economy call). RES2SOIL project (PID2021-126349OB-C22) and P. Campos (PTA2023-023661-I) thank funding from MICIU/AEI (10.13039/501100011033) and the EU (FEDER, NextGenerationEU/PRTR) We thank Verónica Asensio and Rubén Leboreiro for their support, and Antonio Bejarano Moreno (Autoridad Portuaria de Sevilla) for providing access to the field plot area.

Rock-enhanced (RE-)biochars, produced by co-pyrolysis of silicate rock powder with biomass, were proposed to combine pyrogenic carbon capture and storage (PyCCS) with enhanced rock weathering (ERW) as complementary carbon dioxide removal approaches. Catalytic effects of rock-derived AAEM on pyrolysis and carbon speciation were anticipated. Here we produced six RE-biochars (10–90% rock content) by co-pyrolysis of basanite rock powder with wood at contrasting highest treatment temperatures of 450 °C and 750 °C. To provide an in-depth physico-chemical characterization of the RE-biochars, focusing on the biochar-mineral interface region, analytical methods including random reflectance, fast field cycling proton nuclear magnetic resonance relaxometry and electron energy loss spectroscopy were employed. While most treatments had limited effect on the biochar carbon yield (y _c ) and aromaticity of the pyrogenic carbon, RE-biochar produced at 750 °C and containing 90% rock showed an increased hydrogen to carbon molar ratio (H:C _org ), which we partly explained by i) contribution of geogenic hydrogen, ii) physical adsorption of hydrogen to minerals and iii) pyrogenic coating of rock particles with secondary char containing aliphatic- and carboxylic moieties. Still, we cannot fully identify the reasons for increased hydrogen content with constant aromaticity. A decreased reflectance (Ro) and thermal stability (BC _1000C ) for RE-biochars with 90% rock content, despite similar aromaticity as quantified by hydropyrolysis, highlight the limitations of analytical methods developed for carbonaceous materials in the assessment of high ash biochars. Co-pyrolysis can reduce metal oxides, such as hematite (Fe-III) to magnetite, producing (potentially) reactive metals species and can accumulate geogenic potassium (K) at micron scale at rock particle surfaces. This study provides evidence that co-pyrolysis of biomass and basanite does not increase y _c but alters the mineral speciation and elemental distribution at the surface of rock particles. These findings may be further exploited in the design of functionalized RE-biochars and in ERW research.

Global population growth is increasing pressure on agricultural systems, which must boost food production while contending with climate change and the environmental impacts of unmanaged agricultural waste [1]. In this context, the valorisation of agricultural residues has gained importance as a strategy consistent with circular economy principles and supported by European initiatives focused on soil restoration [2]. Pyrolysis has emerged as a key technology for transforming biomass into value-added products such as syngas, biochar, and the liquid fraction bio-oil. However, the aqueous liquid co-product known as pyroligneous acid (PA, or wood vinegar) remains comparatively underexplored, despite its diverse bioactive properties and dose-dependent effects on soils and plants. A deeper understanding of its agronomic and environmental implications, particularly regarding soil processes and carbon dynamics, is crucial for advancing sustainable waste-valorisation strategies.To address this gap, a short term field experiment was conducted to evaluate the safety of PA application under real conditions and its effects on soil carbon storage in the framework of the PIROVALOR project. PA was produced through pyrolysis of mixed wood-waste biomass at 500 °C in a continuous feed cylindrical reactor (Euthenia Energy, Lucena, Spain) and applied to a calcareous sandy loam (Calcic Cambisol) at a 50% (v/v) dose in ‘La Hampa’ farm (Seville, Spain). Soil samples were collected one and six months after application.Preliminary results show that PA is free of pollutants and contains important macro and micronutrients, including Fe, Ca and N. Its application did not alter key agronomic or physicochemical properties, such as soil moisture, penetration resistance, bulk density, pH or electrical conductivity likely due to the strong buffering capacity of the calcareous soil. Short-term compositional changes were observed: total organic carbon and total nitrogen increased one month after application, returning to baseline levels by six months. Notably, PA enhanced the proportion of recalcitrant and intermediate soil organic matter fractions, suggesting the initiation of mechanisms that may contribute to longer-term carbon stabilization.These findings indicate that PA can be applied safely under field conditions and may promote mechanisms of soil carbon stabilization, supporting its potential role within circular and sustainable biomass-valorisation strategies.References:[1] Kurniawati, A., Stankovics, P., Hilmi, Y.S., Toth, G., Smol, M., Toth, Z., 2023. Sustain. Chem. Climate Action, 3, 100033.[2] Márquez-Moreno, J., Sánchez-Martín, Á., Pérez-Dalí, S. M., Rodríguez-López, C., Campos, P., Moreno-Robles, A., Souza-Alonso, P., López-Núñez, R., De la Rosa, J.M., 2025. Waste Management, 210, 115243.Acknowledgement: The Ministry of Science, Innovation and Universities, the State Research Agency (MICIU/AEI/10.13039/501100011033) and the European Union (FEDER and Next Generation EU/PRTR) are thanked for funding the PIROVALOR (CPP2023-010757), RES2SOIL and AGRORES (PID2021 126349OB-C22 – PID2021 126349OB-C21) projects and the contract of P. Campos (PTA2023-02366-I). The technical support and collaboration of Euthenia Energy in the framework of the PIROVALOR project is also acknowledged.