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Improving soil health through nature-based solutions: the effects of olive-pomace-based composts
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Advisor(s)
Abstract(s)
Loss of soil organic matter (SOM) is a major issue in Mediterranean regions, especially in NE Portugal,
where about 70% of soils are classified as Leptosols. On the other hand, olive groves dominate the
region's farmland, and the olive oil industry generates large quantities of by-products. Two-phase olive
pomace (OP) has a high organic load and is phytotoxic due to its high phenolic content. Composting OP
with other agri-residues offers a nature-based solution that addresses untreated OP disposal challenges
while recycling nutrients and supporting the circular economy.
This study evaluates the effects of olive pomace-based composts (OPC) on soil physical and chemical
properties. OPC was produced by composting OP with sheep manure and almond shells. In a pot trial, 3
OPCs produced with different %OP (OPC44, OPC31 and OPC25) and a commercial organic corrective
(HMC) were incorporated in the 0-5cm layer of an eutric Leptosol (2.1% OM) at three doses (10, 20, 40
t.ha-1) + control. Pots were seeded with Italian ryegrass (Lolium multiflorum) and watered to keep soil
moisture above 70% field capacity. After 138 days trial, soil properties were analysed for SOM and its
physical fractionation, total C and N, extractable K, P Olsen, pH, effective cation exchange capacity
(CEC), bulk density, porosity, field capacity, and aggregate stability.
Multivariate analysis showed that compost dose had a stronger influence on soil properties than
compost type. Linear regression revealed that SOM, total C, extractable K, pH and effective CEC
increased proportionally with dose. The highest dose led to SOM and total C increases of 13.3 and 8.4
g·kg⁻¹, respectively. Compared to HMC, OPCs were better K sources. Organic amendment decreased
bulk density (by 8-15%) and increased soil porosity, field capacity, and improved aggregate stability by
~20% (particularly with OPC31 and OPC44).
OPC application also enhanced both physical and chemical protection of SOM. C content was highest
in macroaggregates, stored as unprotected and coarse particulate OM. Higher doses — especially of
OPC31 and OPC44 — promoted larger C accumulation in strongly physically and chemically protected
pools, as compared to control and HMC. OPCs application increased mineral-associated OM, likely due
to their colloidal nature, supporting long-term SOM stabilization.
This study highlights the potential of OPC to improve SOM content, fertility, and soil structure in
degraded Mediterranean soils. Composting OP provides a sustainable approach to valorise agri-waste,
enhance soil functions, and support climate-smart agriculture.
Description
Keywords
Olive groves
Pedagogical Context
Citation
Royer, Ana Caroline; Lado, Marcos; Fonseca, Felícia; Hernandez Hernandez, Zulimar; Figueiredo, Tomás d'Aquino (2025). Improving soil health through nature-based solutions: the effects of olive-pomace-based composts. In Advancing Soil Knowledge for a Sustainable Future - EUROSOIL 2025: Book of Abstracts. Sevilla. ISBN 978-84-09-75471-7
Publisher
Digital.CSIC