How biochar-based fertilizers and biochar compost affect nutrient cycling and crop productivity

Nutr Cycl Agroecosyst (2024) 128:411–414 https://doi.org/10.1007/s10705-024-10358-5 EDITORIAL How biochar‑based fertilizers and biochar compost affect nutrient cycling and crop productivity Leônidas Carrijo Azevedo Melo · Miguel Ángel Sánchez‑Monedero Received: 9 May 2024 / Accepted: 9 May 2024 / Published online: 13 June 2024 © The Author(s), under exclusive licence to Springer Nature B.V. 2024 Over the last two decades, biochar technology has emerged as a promising solution for carbon sequestration in soil. Biochar is a carbon-rich material produced by heating biomass in a low-oxygen environment, which can be beneficial as soil amendment in climatesmart agriculture due to its soil quality-enhancing properties and long-lasting effects (Singh Yadav et al. 2023). This technology not only aids in mitigating climate change but also aligns with the principles of the circular economy to recycle organic residues (Huang et al. 2023; Yang et al. 2023) and to improve soil fertility (Ding et al. 2016; El-Naggar et al. 2019). Metaanalyses have robustly shown the effect of biochar in enhancing crop productivity, with an average increase of 14.5% considering field studies only (Han et al. 2023), and a larger impact in low fertility soils, which encourage the targeted selection of the most suitable biochars to fulfill the requirements for a particular soil and/or land-use prior to soil application (Jeffery et al. 2017; Ye et al. 2020). However, the use of biochar as a soil amendment could become more attractive L. C. A. Melo (*) Soil Science Department, School of Agricultural Sciences, Federal University of Lavras, Lavras, MG 37200‑900, Brazil e-mail: M. Á. Sánchez‑Monedero Department of Soil and Water Conservation and Organic Waste Management, CEBAS-CSIC, Campus Universitario de Espinardo, 30100 Murcia, Spain to farmers if biochar is enriched with nutrients, thus generating a value-added biochar product (Robb et al. 2020). Nonetheless, claims of carbon credits associated with CO2 removals are only possible when the activity is additional. That is, they would not have happened without project financing from the sale of the CO2 removal credits (Salma et al. 2024). Biochar can offer a suitable matrix to produce enhanced-efficiency fertilizers due to its unique properties, such as the ability to retain nutrients, improve soil structure and water-holding capacity, and enhance microbial activity in the soil (Chen et al. 2018). These biochar-based fertilizers are emerging (Fig. 1a) as a cost-effective technology due to the enhanced nutrient use efficiency and associated lower biochar application rates needed for effects on plants (Melo et al. 2022). The low application rates of biochar-based fertilizers (usually < 1.0 Mg ha−1) as required to fulfil crop needs could thus facilitate large-scale biochar application (Melo et al. 2022). Recently, significant advancements have been made in the development, synthesis, application, and understanding of the potential mechanisms behind biochar-based fertilizers, particularly in terms of their slow-release properties and enhanced efficiency (Wang et al. 2022), which ultimately can reduce the carbon footprint in agricultural production. Various methods have been proposed for the synthesis of biochar-based fertilizers, including pyrolysis of nutrient rich feedstock, co-pyrolysis, impregnation with nutrient solutions, encapsulation, and granulation (Sim Vol.: (0123456789) 13 412 Nutr Cycl Agroecosyst (2024) 128:411–414 60 600 a b 500 Number of articles Number of articles 50 40 30 20 10 400 300 200 100 0 0 2014 2016 2018 2020 2022 2024 Year 2014 2016 2018 2020 2022 2024 Year Fig. 1  Number of scientific articles over the last decade on “biochar-based fertilizers” (a) and on “biochar and compost” (b). Search on 31 January 2024 on the Web of Science et al. 2021). The optimization of the nutrient retention and slow-release properties of biochar similarly represent an active research topic that requires further investigation (Rasse et al. 2022). Therefore, there is a need for the development and selection of appropriate production methods aimed at facilitating real-world field applications across various scenarios. The integration of biochar in composting has also attracted great interest in the last decade (Fig. 1b) as a means to optimize the composting process and improve the quality of the final product (Antonangelo et al. 2021; Zhou et al. 2022; Qian et al. 2023), commonly referred to as COMBI (mixture of COMpost and BIochar). When added to the composting pile, biochar modifies key parameters of the composting process (e.g., O2, carbon/nitrogen (C/N) ratio, pH, temperature, water content), reducing not only the composting time (Sánchez-García et al. 2015), but also emissions of ammonia (Zhang et al. 2021), methane (Harrison et al. 2022), and associated odor-related issues (Nguyen et al. 2023). Availability of heavy metals in COMBI, such as zinc or copper, is also reduced (Zhou et al. 2022). Upon addition to agricultural land, COMBI has been shown to generate lower nutrient leaching losses and lower GHG emissions relative to the application of compost without biochar (Gao et al. 2023). Thus, the integration of biochar into composting processes presents a promising avenue for sustainable agricultural practices and environmental stewardship. Besides the co-composting process, COMBI can also be manufactured by the physical mixture of mature compost and biochar, with or without an incubation period (Khan et al. 2023). The combined application of biochar and compost has potential to generate benefits to a larger Vol:. (1234567890) 13 extent than their application alone due to their complementary properties, such as the amounts of nutrients and the combination of labile and stable carbon fractions and chemical functional groups (Khan et al. 2023). Optimizing the biochar-to-compost ratio based on macronutrient analysis is crucial for maximizing environmental and ecological benefits. This ensures an optimal nutrient balance for plant growth, reduces nutrient runoff, and enhances sustainability in agriculture practices. Biochar can also be used as a sustainable alternative component in growing media that works as a peat substitute. This aims to reduce the environmental impact of peat mining and contributes to the circularity of horticultural systems (Dunlop et al. 2015). This Special Issue on biochar-based fertilizers contains articles dealing with potassium (K) enrichment of such fertilizers (Fachini et al. 2023), COMBI (Lebrun et al. 2023), and growing media (Vandecasteele et al. 2023). Fachini et al. (2023) evaluated the performance of K-enriched biochar-based fertilizers in supplying nutrients to radish plants. Biochar-based fertilizers were based on sewage sludge biochar enriched with K using muriate of potash (KCl). The study found that both pellet and granule forms of biochar-based fertilizers were efficient in supplyin (...truncated)