Fertilization strategies to reduce yield-scaled N2O emissions based on the use of biochar and biochar-based fertilizers

Nutr Cycl Agroecosyst https://doi.org/10.1007/s10705-023-10313-w ORIGINAL ARTICLE Fertilization strategies to reduce yield‑scaled N2O emissions based on the use of biochar and biochar‑based fertilizers Raúl Castejón‑del Pino · Miguel A. Sánchez‑Monedero · María Sánchez‑García · María L. Cayuela Received: 29 May 2023 / Accepted: 27 August 2023 © The Author(s) 2023 Abstract Novel fertilization strategies, such as the use of biochar-based fertilizers (BBFs) and the coapplication of biochar with mineral fertilizers, have shown promising results for mitigating nitrous oxide (N2O) emissions and reducing N losses in agroecosystems. Two greenhouse experiments were performed with radish to evaluate: (1) the mitigation of yield-scaled N2O emissions using BBFs, produced at either 400 or 800 °C and enriched with urea, compared to the co-application of raw biochars with urea; and (2) the N 2O mitigation potential of low rates of raw biochars, equivalent to those used with BBFs fertilization, co-applied with low and high N rates (90 and 180 kg N ha−1). BBF produced at 800 °C reduced yield-scaled N2O emissions by 32% as compared to the urea treatment, and by 60%, as compared to the combination of raw biochar with urea. This reduction was attributed to the slow rate of N release in BBF. On the contrary, the co-application of low rates of biochar with urea increased yield-scaled N2O emissions as compared to the fertilization with urea Supplementary Information The online version contains supplementary material available at https://doi. org/10.1007/s10705-023-10313-w. R. Castejón‑del Pino (*) · M. A. Sánchez‑Monedero · M. Sánchez‑García · M. L. Cayuela Department of Soil and Water Conservation and Organic Waste Management, CEBAS-CSIC, Campus Universitario de Espinardo, 30100 Murcia, Spain e-mail: alone. Low rates of biochar (1.4–3.1 t h a−1) reduced yield-scaled N2O emissions only with a high rate of N fertilization. High-pyrolysis-temperature biochar, co-applied with synthetic fertilizer, or used to produce BBFs, demonstrated lower yield-scaled N2O emissions than biochar produced at a lower pyrolysis temperature. This study showed that BBFs are a promising fertilization strategy as compared to the co-application of biochar with synthetic fertilizers. Keywords Raphanus sativus · GHG · Olive tree pruning · N-enriched biochar · Activated biochar · N2O emission factor Introduction Fertilized soils represent the highest source of direct and indirect nitrous oxide (N2O) emissions in agriculture (FAO 2020). This greenhouse gas (GHG) contributes to both increasing global temperatures and depleting the ozone layer (Myrold 2021). There is a high urgency to mitigate N2O emissions from agricultural lands (Tian et al. 2020). However, in order to guarantee food security, mitigation practices need to address potential trade-offs with crop yields (Grados et al. 2022). Thus, in order to evaluate the mitigation potential of a given agricultural practice, the determination of yield-scaled N2O emissions or N2O-intensity is a better option than area-scaled N2O emissions, as the former contemplates N 2O emissions Vol.: (0123456789) 13 Nutr Cycl Agroecosyst per crop unit or N taken up by crops (Van Groenigen et al. 2010). Recently, Grados et al. (2022) evaluated the efficiency of the most widely adopted N2O mitigation practices. They identified some technology-driven solutions, such as the application of urease/nitrification inhibitors, the adoption of drip irrigation, and the use of biochar as the most promising strategies to reduce emissions without compromising crop production. The co-application of biochar with fertilizers is a well-documented strategy to mitigate GHG emissions, in particular N 2O, and to increase C sequestration in soil (Joseph et al. 2021). N2O mitigation with biochar is associated with its ability to retain N and promote the last step of denitrification, thereby decreasing the N 2O/(N2O + N2) ratio (Cayuela et al. 2013; Van Zwieten et al. 2014). In addition, the characteristics of the biochar influence its mitigation potential. Thus, the higher the aromaticity of biochar (due to high pyrolysis temperatures), the higher the reduction in N2O emissions (Cayuela et al. 2015). In order to guarantee the sustainability of biochar as a GHG mitigation strategy, several aspects need to be considered. First, it is important to avoid large scale biochar production from both biomass crops and forest wood, as this could lead to land use change and deforestation in some areas (IPCC 2023). In contrast, biochar produced from agroforestry residues is an environmentally and economically feasible practice that can contribute to a circular economy (Robb et al. 2020; Azzi et al. 2021). A second aspect to consider is biochar application rate. The cost of producing and applying biochar into soil may be economically unviable if the biochar application rate is high (Baveye 2023). On the other hand, the biochar application rate is known to directly correlate with its N 2O mitigation potential (Cayuela et al. 2014; Rittl et al. 2021), with rates lower than 10 t ha−1 not having a significant effect on N2O emissions (Borchard et al. 2019). Studies using lower rates showed a limited effect or even a promotion of N2O emissions (Kaur et al. 2023). To date, research using biochar at low rates (< 5 t ha−1) is limited, and further knowledge is needed. Additionally, when biochar is co-applied in soil with synthetic fertilizers, the higher the N rate (such as those used in intensive agriculture), the higher the biochar N 2O mitigation (Sun et al. 2017; Wang et al. 2020). Studies that compared increasing N fertilization rates used moderate biochar Vol:. (1234567890) 13 application rates, but there is a need for information on biochar application rates < 0.5% w/w (or < 10 t ha−1). Recently, the interest on the application of biochar enriched with nutrients, such as N, is rapidly growing. Nutrient-enriched biochars are known as biochar-based fertilizers (BBFs), although some authors referred to them as BCFs or BFs. BBFs use has been described as an efficient strategy to mitigate GHG and to increase N use efficiency (Puga et al. 2020a; Rasse et al. 2022; Zhang et al. 2023). BBFs may reduce N2O and CH4 emissions with a moderate cost to farmers (Joseph et al. 2021). Thus, BBFs have been regarded as the most cost-effective option for biochar use, as they are usually applied at low rates (< 5 t h a−1) (Robb et al. 2020). Nonetheless, the associated generation of C credits is also small. Several pre- and post-pyrolysis treatments have been developed to enrich biochar with N (Ndoung et al. 2021). Pre-pyrolysis treatments usually produce BBFs with highly recalcitrant N, whereas post-pyrolysis treatments commonly produce BBFs with slow-release N (Marcińczyk and Oleszczuk 2022). We have recently described post-pyrolysis activation and N-enrichment methods that efficiently incorporate different N forms that could b (...truncated)