Field application of pyroligneous acid enhances soil properties and supports Carbon stabilization pathways

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.