Sustainable Fertilizers: Utilizing Biomass Ashes and Biochars

Inhaltsverzeichnis

1. Frontmatter

2. 1. Introduction to Precision Agriculture

   Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

   Abstract

   Agriculture today faces the dual challenge of ensuring sufficient food production for a growing population while preserving the environment. The intensification of agricultural production in the twentieth century, based on artificial fertilizers and agrochemicals, has significantly increased yields, but has also caused a number of environmental problems: soil degradation, water pollution, greenhouse gas emissions, and loss of biodiversity (Sharma et al. in Discov. Sustain. 5(1):1–14, 2024 [1]). In the face of these threats, the concept of sustainable agriculture has gained crucial importance—it is considered the foundation for ensuring food security and improving the quality of life of societies (Polcyn et al. in Sustainability 15(23):16415, 2023 [2]). Sustainable agriculture seeks to manage production in a way that increases yields in an environmentally friendly manner, reduces ecosystem degradation, and conserves resources for future generations (Chen et al. in J. Clean. Prod. 17, 142606, 2024 [3]). Achieving these goals, however, requires innovative solutions, including alternative fertilizers and soil improvers that maintain or increase soil fertility and yields with less chemical pressure on the environment (Panwar et al. in SN Appl. Sci. 1(2):1–19, 2019 [4]).

3. 2. Biomass Ash Definition and Types of Biomass Ash

   Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

   Abstract

   Biomass ash is the inorganic, non-combustible fraction that remains after the complete or partial oxidation of plant- or animal-derived biomass (e.g., wood, straw, poultry litter, sewage sludge) and is now viewed as a secondary nutrient source in circular agriculture. It represents the non-combustible mineral fraction and is increasingly viewed as a secondary nutrient source within circular agriculture frameworks (Maj et al. in Sustainability 17(11):4925, 2025 [1]). The progressive substitution of fossil fuels by biomass has been accompanied by a steady rise in ash production. Recent energy-balance studies estimate global biomass ash output at approximately 40–60 Mt yr⁻¹, which is about one order of magnitude lower than earlier headline values (Romanowska-Duda et al. in Molecules 29(18), 2024 [2]). Although management of this by-product poses logistical challenges, the ash represents a potential nutrient resource owing to its mineral content. Historically, ash derived from biomass combustion-wood ash in particular-served as one of the earliest mineral fertilizers. Agricultural application of ash enabled partial restitution of nutrients removed during crop harvest (Barišić et al. in Materials 15(13), 2022 [3]). Contemporary circular-economy strategies advocate recycling of biomass ash to minimize disposal and close elemental loops (Tosti et al. in Waste Biomass Valorization 12(8):4703–4719, 2021 [4]).

4. 3. Biochars

   Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

   Abstract

   Biochar is a solid, porous carbon material obtained from biomass through pyrolysis, a thermochemical process carried out under conditions of limited oxygen access (Youngsang et al. in BioRes_16_3_6512_Chun_LYK_Review_Recent_Biochar_Prodn_Biomass_Classif_Pyrol_18707, 2021 [1]; Varkolu et al. in Catalysts 15(3), 243, 2025 [2]). In practice, biochar is a type of charcoal of plant origin, produced from various organic raw materials, such as wood waste, straw and crop residues, animal manure, or sewage sludge (Tomczyk et al. in Rev. Environ. Sci. Biotechnol. 19(1):191–215, 2020 [3]). During pyrolysis, organic material is subjected to high temperatures (usually 300–700 °C) in an oxygen-free atmosphere, resulting in its decomposition into three fractions: gaseous (syngas), liquid (bio-oil), and solid (biochar) (Varkolu et al. in Catalysts 15(3), 243, 2025 [2]).

5. 4. Application of Biomass Ash and Biochars as Fertilizers

   Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

   Abstract

   Biomass ash and biochar are gaining increasing interest as alternative or supplementary fertilizers in agriculture and forestry. Both products are made from plant materials. Biomass ash through full combustion of biomass, while biochar through incomplete combustion (pyrolysis) under oxygen-limited conditions. The use of these products fits in with the idea of a closed-loop economy. It allows nutrients to be recycled from plant waste back into the soil, reducing the use of conventional mineral fertilizers and landfill. The following chapter discusses methods for the application of biomass ash and biochar to soil, reviews research results on their effectiveness and provides examples of practical use in different types of crops.

6. 5. Impact on Crop Yield and Quality

   Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

   Abstract

   Recent energy-balance studies put worldwide biomass ash production at roughly 40–60 million tons per year, not hundreds of millions (Vassilev et al. in Fuel 129:292–313, 2014 [1]; Romanowska-Duda et al. in Molecules 29(18):4397, 2024 [2]). Because wood- or straw-derived ash is rich in K, Ca, Mg, P, and micronutrients, it can be reused as a nutrient input in circular agriculture; yet trace Cd, Pb and Hg may still occur, so every batch should be tested to confirm it meets fertilizer-quality limits (Buss et al. in J. Clean. Prod. 208:960–967, 2019 [3]). Biochar is a highly carbonized material obtained in controlled pyrolysis of biomass (with limited oxygen). It is characterized by high porosity, high specific surface area, and an alkaline reaction (Antonangelo et al. in Biochar 7(1):1–28, 2025 [4]).

7. 6. Effects of Biomass Ash and Biochars on Soil Properties

   Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

   Abstract

   Biomass used for energy purposes generates two important byproducts: the ash produced after its combustion and the biochar obtained through pyrolysis. Both of these materials are used as soil additives, attracting much interest in the last decade. Biomass (e.g., wood) ash is increasingly treated as a substitute for lime and mineral fertilizer—when added to soil, it reduces its acidification and enriches it with nutrients (Błońska et al. in Geoderma Reg. 34:e00676, 2023 [1]). Biochar, on the other hand, is defined as a highly carbonized, porous material formed from biomass under anaerobic conditions that has a high content of stable carbon. Research indicates that biochar is a multifunctional, sustainable soil improver that increases soil fertility, captures contaminants and contributes to improved plant growth (Sharma in Saudi J. Biol. Sci. 28:7539, 2021 [2]). Also important is the long-term fixation of carbon in the soil after biochar application, which promotes carbon sequestration and climate change mitigation (Singh et al. in Biochar 4:1–17, 2022 [3]). Both ash and biochar introduced into the soil have a complex effect on a number of physical, chemical, and biological properties of that soil.

8. 7. Policy and Regulatory Framework

   Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

   Abstract

   The use of ashes from biomass combustion and biochar as fertilizers or soil improvers is gaining increasing attention in the context of a circular economy and sustainable agriculture. Biomass ash contains macronutrients (e.g., potassium, phosphorus, and calcium) and can increase soil pH, while biochar has high stability in soil and the ability to sequester carbon, helping to improve soil fertility and water retention. Despite these benefits, it is crucial that an appropriate legal framework and quality standards are in place to ensure the safe and effective use of these materials. Efforts have been made both internationally and in the European Union to regulate the status of biomass ash and biochar—from legal classification, to quality requirements, to their inclusion in the official fertilizer cycle (Silva et al. in J. Clean. Prod. 214:112–124, 2019 [1]; Jarosz-Krzemińska and Poluszyńska in Energies 13(18):4805, 2020 [2]). This chapter presents the current regulation of biomass ash and biochar-based fertilizers, discusses quality and safety standards for these products, and examines future agricultural policy perspectives in this area.

9. 8. Sustainable Development and Environmental Protection

   Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

   Abstract

   Ash from biomass combustion and biochar produced in the biomass pyrolysis process are becoming important elements of the circular economy and sustainable development. Biochar is recognized as a carbon dioxide removal (CDR) technology that promotes food security, sustainable land management, and the circular economy (Weng and Cowie in Commun. Earth Environ. 6(1):1–9, 2025 [1]). Ash, on the other hand, is an unavoidable by-product of thermal biomass processing and is often still treated as waste stored in landfills—currently, only a small fraction of biomass ash is recycled (Viola et al. in Low-Carbon Mater. Green Constr. 2(1):1–14, 2024 [2]). Meanwhile, both biochar and ash can be reused in ways that bring significant environmental and climate benefits. This chapter discusses how the use of ash and biochar fits into the goals of sustainable development and environmental protection. It presents their role in reducing greenhouse gas emissions and carbon sequestration, their importance in waste management and biomass recycling, as well as the long-term environmental benefits of their use. Particular emphasis is placed on current global trends and research findings in this area.

10. 9. Conclusion

    Katarzyna Chojnacka, Filip Gil, Dawid Skrzypczak, Grzegorz Izydorczyk

    Abstract

    Biomass ash and biochar emerge from the present analysis as promising and sustainable soil amendments that can partially substitute for conventional mineral fertilizers. Biomass ash, generated as a residue from the combustion of woody and herbaceous biomass, contains significant amounts of macronutrients such as calcium, potassium, phosphorus, and magnesium. Its alkaline nature enables effective neutralization of acidic soils. For this reason, biomass ash is often considered functionally comparable to liming agents. In nutrient-poor soils, it provides essential elements that are readily available to plants. Biochar, by contrast, is produced through the pyrolysis of biomass under limited oxygen conditions. It is characterized by a high proportion of stable organic carbon that resists biological degradation, making it an efficient long-term carbon sink in soils, potentially lasting hundreds or even thousands of years. Its porous structure and large surface area enhance the soil’s cation exchange capacity and water retention potential, thereby improving fertility and reducing nutrient losses from the soil profile.