Biochar for Productive Soil: Biochar stability / Valorization of Biochar as a Fertilizer
Abstract
PYSOLO Mid-term Stakeholder Event on Solar-driven Biomass Pyrolysis on 6 November 2025 in Zaragoza, Spain The PYSOLO (PYrolysis of biomass by concentrated SOLar pOwer) project consortium invited stakeholders from industry, academia, agriculture, and policy to attend the Mid-Term Stakeholder Event of the Horizon Europe project held in Zaragoza, Spain, on 6 November 2025. This event highlighted recent progress in solar-driven biomass pyrolysis – a combination of technologies with significant potential for industrial decarbonisation and defossilisation, circular bioeconomy, and climate change mitigation. The half-day program provided participants with a comprehensive overview of PYSOLO’s current results. The first session featured presentations on the concentrated solar power technology, the pyrolysis units, the biomass selection, and the pyrolysis products with a special focus on biochar. It also provided the opportunity for an open dialogue with the project team. The second part included an exclusive guided tour of the ICB-CSIC (Instituto de Carboquímica) research facilities, where one of the project’s pyrolysis units is being developed and tested. Agenda: Welcome and opening of the meeting - Marco Binotti (Politecnico di Milano) & Tomás García (Consejo Superior de Investigaciones Científicas (CSIC)) The PYSOLO Project: concept at a glance - Marco Binotti (Politecnico di Milano) Development of solar rotary kiln technology at the DLR for heating and treatment of particles - Juan Pablo Rincon Duarte (Deutsches Zentrum für Luft und Raumfahrt) Pyrolysis technologies for solar integration - Andrea Maria Rizzo (RE-Cord) & José Manuel Lopéz Biochar for Productive Soils: Early Insights from Zaragoza Trials - David Casini & Ana Simões Mota Overall PYSOLO system performance - Marco Colombi (Politecnico di Milano) Mapping Forest and Agrucultural Biomass and Assessmen for Biorefineries in the Mediterranean Region - Ercio Kutchartt (Centro de Ciencia y Tecnología Forestal de Cataluña (CTFC))
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Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Climate, Infrastructure and Environment Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. Biochar stability D. Casini, A.M. Rizzo, D. Chiaramonti Ing. David Casini – RE-CORD Stakeholder Event, November 6th, 2025, Zaragoza [ES]
Biochar stability Ing. David Casini –RE-CORD Stakeholder Event, November 6th, 2025, Zaragoza [ES] 2 BCR and inertinite assessment
www.pysolo.eu Biochar stability Stakeholder Event, David Casini, November 6th, 2025 3 << Carbonization reactions converts the organic matter into a more durable form of carbon, slowing down the return of a portion of this carbon to the atmosphere by microbial activity in soil and sediments. [...] at pyrolysis temperatures typically at 550–600 ◦C >>
www.pysolo.eu Stakeholder Event, David Casini, November 6th, 2025 4 STABLE C, RECALCITRANT FORM LABILE C, DECOMPOSITION AND MINERALIZATION CO2 RELEASE BCR •BCR enables the capture and sequestration of atmospheric C by combining photosynthesis and carbonization of biomass •CO2is captured by plants through photosynthesis, then the largest share of carbon is converted into into durable C through pyrolysis and stored in biochar Biochar Carbon Removal
www.pysolo.eu Stakeholder Event, David Casini, November 6th, 2025 5 Inertinite is agroup of inert organic components found in coal and other carbonaceous materials. It is ahighly durable form of carbon, making it very resistant to chemical and biological degradation (will not relevantly degrade in soils within climate-relevant periods). Inertinite assessment Random reflectance is a new method to determine the various C shares in biochar. The analysis recognizes these various Carbon forms in biochar via light reflectance.
www.pysolo.eu Stakeholder Event, David Casini, November 6th, 2025 6 Random reflectance analysis for biochar is used to determine the degree of carbonization of the material. The test measures how much light is reflected from the biochar's surface. •Ro < 1.2%: Poorly carbonized fraction (less stable carbon) •1.2% < Ro < 2.0%: Semi-inertinite fraction (intermediate stability) •Ro > 2.0%: Inertinite fraction (highly stable carbon) Random reflectance
www.pysolo.eu Stakeholder Event, David Casini, November 6th, 2025 7 Random reflectance analysis for biochar is used to determine the degree of carbonization of the material. The test measures how much light is reflected from the biochar's surface. •Ro < 1.2%: Poorly carbonized fraction (less stable carbon) •1.2% < Ro < 2.0%: Semi-inertinite fraction (intermediate stability) •Ro > 2.0%: Inertinite fraction (highly stable carbon) Random reflectance
www.pysolo.eu Random reflectance Stakeholder Event, David Casini, November 6th, 2025 8 88 Distribution of the different fractions of organic carbon on a dry basis (including also mineral carbon) Results permit to quantify the stable fraction of organic carbon which contribute to long-term carbon sequestration
www.pysolo.eu 9 Thank you! PYSOLO -Stakeholder Event 6 November 2025 [email protected]
www.pysolo.eu Sampling plan and methodology 7Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 T1 T2 T3 07-2025 04-2025 11-2024 Experiment established Baseline sampling for soil description GHG emissions (CO2, CH4, N2O): -7 days after N fertilization (Nov/Mar) -every 2 weeks -after rainfall Microbial biomass Microbial respiration Mid-Term SOC + N Enzymes * All soil indicators Crop parameters β-Glucosidase (carbon turnover) Urease (nitrogen availability) Dehydrogenase (overall microbial activity).
www.pysolo.eu Methodology 8Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 Category Main Indicators Purpose Soil Physical Properties Bulk density, texture, water retention How biochar changes soil structure and water storage Chemical Fertility pH, EC, CEC, carbonates, total N, ammonium -N, nitrate-N How nutrients are stored, released, and balanced Organic Carbon & Fractions SOC, particulate organic C fractions (<250 µm, etc.), poxC How stable and active forms of carbon evolve Biological Activity Microbial biomass, enzyme activity, soil respiration How soil life responds and supports nutrient cycling Greenhouse Gas Fluxes CO ₂, N₂O, CH₄sampling Biochar’s climate impact and mitigation potential Crop Response Yield, grain quality (Dick -Jones and others) Final proof of agronomic and economic benefit
www.pysolo.eu Experimental Design -Greenhouse 9Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 Treatments C: Baseline control LB: Low Biochar (2 t/ha) MB: Medium Biochar (6 t/ha) HB: High Biochar (20 t/ha) LB + MF: Low Biochar (2 t/ha) + MF MB + MF : Medium Biochar (6 t/ha) + MF HB + MF : High Biochar (20 t/ha) + MF MF: Fertilizer control LBO: Low Biochar-oil (2 t/ha) MBO: Medium Biochar-oil (6 t/ha) HBO: High Biochar-oil (20 t/ha) LBO + MF: Low Biochar-oil (2 t/ha) + MF MBO + MF : Medium Biochar-oil (6 t/ha) + MF HBO + MF : High Biochar-oil (20 t/ha) + MF + bauxite test BAUL:Low Bauxite Biochar (2 t/ha) BAUM: Medium Bauxite Biochar (6 t/ha) BAUH: High Bauxite Biochar (20 t/ha)
www.pysolo.eu Methodology -Greenhouse 10Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 Category Main Indicators Purpose Soil Physical Properties Bulk density, AWCH (available water holding capacity) Assess how biochar affects soil structure, porosity, and water retention. Soil Chemical Fertility pH, EC, CEC, carbonates (CaCO₃), total N, available P, exchangeable K, Ca, Mg, Na, micronutrients (Fe, Mn, Zn, Cu) Evaluate nutrient availability, retention, and overall soil chemical balance. Organic Carbon & Fractions TOC, POC, MaOC Determine how biochar influences organic matter pools and carbon stabilization. Biological Activity Basal respiration, microbial biomass, enzymatic activities (dehydrogenase, urease, βglucosidase) Measure soil biological functioning and microbial response to treatments. Contaminant Assessment (bauxite biochar only) Heavy metals (Al, Cr, Ni, Pb, Cd) Verify potential contamination risks and trace element immobilization. Plant Establishment & Growth Germination rate, plant height (weekly), phenological stages (Zadoks scale) Monitor crop development and early growth performance under treatments. Plant Nutrient Status & Physiology Chlorophyll content (SPAD readings), nutrient content in plant tissue (C, N, P, K, etc.) Assess plant nutrient uptake efficiency and physiological health.
www.pysolo.eu Analysis progression 11Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 🪴 Year 1 —Foundation Experiment established and monitored under real Mediterranean conditions — soil, crop, and gas data collected. 🔬 Now —Understanding Laboratory analyses in progress to uncover how structure, carbon, and microbes respond to biochar. 🌾 Year 2 —Confirmation Next season will test the consistency of effects on yield, water balance, and long -term soil fertility.
www.pysolo.eu Preliminary results 12 Daily GHG Emissions –CO2-C CO ₂ : Higher overall fluxes in the co-application of biochar + MF. Biochar-only treatments maintained lower, steadier respiration. Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025
www.pysolo.eu 13 Daily GHG Emissions – N2O-N N2O: Spring N₂O peaks coincided with rain and warmer temperatures, indicating environmentdriven ‘hot moments’; MF amplified these pulses, but biochar + MF slightly dampened them. Occasional spikes in MB and controls likely reflect rewetting. Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 Preliminary results
www.pysolo.eu 14 N ₂ O: Over the season, MF drove the largest cumulative losses. The co-application of biochar with MF lowered emissions by ~16%. Biochar alone kept emissions near control levels, reinforcing its low-N₂O footprint. Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 Preliminary results Cumulative Emissions (nov 24 –jul 25)
www.pysolo.eu 15Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 Preliminary results 0 1000 2000 3000 4000 5000 6000 CMF LB MB LB+MF MB +MF Yield (10%) (kg ha-1) b b b a ab ab Biochar alone showed limited yield response Biochar + mineral fertilizer performed similarly to mineral fertilizer alone. These are first-year results —the effect of biochar, being highly recalcitrant, may take longer to become evident Highest yield with mineral fertilizer ≈ 5.2 t ha ⁻ ¹ Lowest yield in control (no fertilization)≈ 2.7 t ha ⁻ ¹ Yield –first campaign (2024-2025) p<0.023
www.pysolo.eu First year learnings 16Ana Simões Mota; Jorge Alvaro-Fuentes -EEAD CSIC | STAKEHOLDER EVENT | 06/11/2025 •Biochar + MF slightly reduced N ₂ O losses, showing potential for mitigation. Biochar without MF had minimal N₂O impact. •Biochar + fertilizer sustained yields; biochar alone had little effect. •CO₂fluxes were less responsive to treatments. •Environmental conditions were triggers for emission peaks during spring fertilization.