PCW Biochar System: Agricultural In-Situ Pyrolysis Combined with Multi-Strata Agroforestry for Large-Scale Carbon Sequestration and Soil Restoration

Abstract This article presents the PCW Biochar System, an approach combining in-situ agricultural pyrolysis and multi-strata agroforestry to increase carbon sequestration while restoring soil fertility. The system is based on two main stages. The first stage consists of producing biochar directly on the field from local biomass using flame-curtain pyrolysis carried out in a biomass windrow. This method converts part of the biomass into stable carbon incorporated into the soil. The second stage involves the development of a high-biomass multi-strata agroforestry system integrating fast-growing trees, giant grasses, nitrogen-fixing plants, and permanent ground cover. Under the studied temperate climate conditions, the system could produce approximately 150 to 180 tonnes of biomass per hectare per year and enable a net storage estimated between 80 and 100 tonnes of CO₂ per hectare per year, including carbon stabilization in soils, woody biomass, and biochar. At large scale, the implementation of this system across several hundred million hectares could represent a significant potential for atmospheric carbon reduction while improving agricultural productivity and soil resilience. The article also highlights that multi-strata agroforestry systems in tropical climates could reach even higher biomass production levels, potentially increasing both biochar yield and carbon sequestration. Introduction Climate change represents one of the major challenges of the twenty-first century. Greenhouse gas emissions resulting from human activities have led to a rapid increase in atmospheric carbon dioxide concentrations. At the same time, many agricultural soils have lost a significant portion of their organic matter, reducing their capacity to store carbon and maintain fertility. In response to these challenges, several strategies have been proposed to increase carbon sequestration in soils. Among them, biochar production and agroforestry systems appear to be particularly promising solutions. The PCW Biochar System proposes to combine these two approaches within an integrated agricultural system capable of producing large quantities of biomass while transforming part of this biomass into stable carbon stored in the soil. General Principle of the PCW Biochar System The PCW Biochar System is based on a biomass management cycle integrating plant production, partial thermal transformation, and carbon stabilization in soils. The system includes two main phases. The first phase consists of producing biochar directly on the field from agricultural biomass using in-situ pyrolysis. The second phase involves the establishment of a multi-strata agroforestry system designed to maximize biomass production and atmospheric carbon capture Initial Biomass Production The first year of the system is dedicated to producing biomass intended for biochar production. The species used are selected for their rapid growth and high biomass productivity. Main species include: Paulownia tomentosa Populus nigra Robinia pseudoacacia Alnus glutinosa Miscanthus × giganteus Cannabis sativa (Tropical systems combining fast-growing nitrogen-fixing trees, giant grasses and bamboo may produce more than 300 tonnes of biomass per hectare annually, potentially enabling large-scale biochar production through decentralized flame-curtain pyrolysis systems.) Fast-growing trees produce woody biomass rapidly and contribute to structuring the future ecosystem. Some species, particularly Robinia pseudoacacia and Alnus glutinosa, also have the capacity to fix atmospheric nitrogen through bacterial symbiosis. The biomass produced during this phase is then used for biochar production. Biochar Production through In-Situ Agricultural Pyrolysis Biochar production is carried out in a biomass windrow placed on the soil surface. The geometry of the windrow is optimized to control combustion and favor pyrolysis. Typical windrow dimensions: base width: approximately 5 meters height: approximately 1.5 meters length: variable depending on the amount of biomass. The biomass is arranged longitudinally in order to facilitate the progression of the pyrolysis front. During controlled combustion, the pyrolysis gases produced by the thermal decomposition of biomass burn in the upper layer of the windrow, forming a flame curtain that limits oxygen supply to the lower layers. This process transforms part of the biomass into biochar rich in stable carbon. Initial Biochar Application After pyrolysis, the biochar is distributed across the field. Typical application rate: 20 to 30 tonnes of biochar per hectare Biochar generally contains 70 to 85% stable carbon. This corresponds to an immediate storage of: 60 to 90 tonnes of CO₂ per hectare Biochar also improves several soil properties: water retention cation exchange capacity microbial activity development of mycorrhizal networks Economic Cost Comparison of the PCW Biochar System and Conventional Biochar Production Technologies Compared with conventional biochar production technologies, the PCW Biochar System significantly reduces operational costs by producing biochar directly on agricultural land using in-situ flame-curtain pyrolysis, thereby eliminating the need for centralized industrial infrastructure and long-distance biomass transport. Industrial pyrolysis plants typically require investments of several million euros and produce biochar at costs ranging from 500 to 1200 € per tonne, while small metal kilns or batch reactors generally produce biochar at 200 to 600 € per tonne, and Kon-Tiki systems at approximately 100 to 300 € per tonne. In contrast, the PCW Biochar System relies primarily on locally produced biomass and standard agricultural equipment, allowing estimated production costs of roughly 30 to 120 € per tonne of biochar, depending on labor and mechanization levels. When converted to carbon removal costs, this corresponds to approximately 7 to 40 € per tonne of CO₂ sequestered, which is substantially lower than most technological carbon removal solutions such as Direct Air Capture (500–1000 € per tCO₂) or BECCS (100–200 € per tCO₂). In addition to its low operational costs, the system also generates indirect economic benefits through improved soil fertility, water retention, and agricultural productivity, making decentralized in-situ biochar production a potentially cost-effective strategy for large-scale carbon sequestration in agricultural landscapes. Multi-Strata Agroforestry System After biochar introduction, the field is organized according to a multi-strata agroforestry system. This system combines several vegetation layers in order to optimize solar capture and biomass production. Typical structure: main canopy of fast-growing trees secondary trees shrubs vines giant biomass plants nitrogen-fixing root meadows permanent ground cover This organization increases photosynthetic density and enhances total biomass production. Annual Biomass Production In a temperate climate, annual biomass production may reach: 150 to 180 tonnes of dry biomass per hectare per year Plant biomass contains approximately 45% carbon. Annual carbon capture may therefore reach: 67 to 80 tonnes of carbon per hectare per year In carbon dioxide equivalent: 245 to 295 tonnes of CO₂ captured per hectare per year Carbon Storage In agroforestry systems, approximately 30 to 40% of captured carbon may remain stored within the ecosystem. Annual storage may therefore reach: 75 to 100 tonnes of CO₂ per hectare per year Carbon is stored in several compartments: biochar soil organic matter deep roots permanent woody biomass Global Deployment Potential If this system were deployed across approximately: 300 million hectares the annual carbon sequestration potential could reach: 24 to 30 gigatonnes of CO₂ per year Potential under Tropical Climates These estimates represent a theoretical large-scale potential and would require major global land-use transformations. Multi-strata agroforestry systems in tropical climates can produce: 250 to 400 tonnes of biomass per hectare per year Under such conditions, biochar production and carbon sequestration could be significantly higher than those observed in temperate climates. Limitations and Uncertainties The estimates presented rely on several simplified assumptions. Actual system performance may vary depending on: climatic conditions initial soil fertility water availability agricultural management practices Experimental studies will be necessary to validate system performance in different contexts. Research Perspectives Future research could focus on: experimental evaluation of soil carbon storage optimization of agricultural pyrolysis techniques selection of high-biomass plant species assessment of tropical agroforestry systems potential Conclusion The PCW Biochar System combines in-situ agricultural pyrolysis with multi-strata agroforestry in order to create a system capable of restoring soils while durably storing carbon. Under optimized conditions, the system could enable net carbon storage estimated at 80 to 100 tonnes of CO₂ per hectare per year. At large scale, such systems could contribute significantly to the reduction of atmospheric carbon while improving soil fertility and the resilience of agricultural systems. Reference Grandjean, Médéric (2026). PCW Biochar System: In-Situ Agricultural Pyrolysis and Multi-Strata Agroforestry as a Strategy for Massive Carbon Sequestration and Soil Restoration. Scientific References The development of the PCW Biochar System builds upon a body of scientific research on soil carbon sequestration, biochar production, and agroforestry systems. Several studies have demonstrated the potential of biochar to improve soil fertility while stabilizing carbo