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The production of novel biobased fertilisers (BBFs) from organic residues presents a growing interest as a measure to reduce reliance on mineral fertilisers. Beside their role as a provider of nutrients, BBFs may have a significant impact on soil C dynamics and sinks.
Assessing the role of BBFs in soil carbon (C) sequestration is crucial for promoting sustainable agriculture, fostering recycling of exogenous organic matter (EOM), and mitigating climate change. This study evaluates the long-term effects of novel BBFs—such as microbial biomass, insect biomass, insect frass, biochar, and their blends—on soil C dynamics using a combination of experimental and modelling approaches. Conducted as part of the H2020 RUSTICA project, the research focuses on how these EOM-derived fertilisers can influence soil organic matter turnover and carbon sequestration potential.
We performed one-month laboratory incubation experiments of soil amended with BBFs and derived blends under controlled aerobic conditions (40% of water holding capacity and 20°C). The CO2-C efflux from the incubated soils was accurately measured (every 4 hours) using an automated GC system. An inverse modelling of the respiratory responses of amended soils was performed with a modified RothC model, enhanced by including additional EOM pools, to estimate EOM pools parameters. The maximum likelihood estimates for EOM pools parameters, specifically pool size and decay rates, were inferred using the Differential Adaptive Metropolis (DREAM) algorithm based on the mineralization rate observed in the experiments. This approach ensured calibration of EOM pool parameters for each BBFs. The modified RothC model with calibrated EOM pools parameters was then used to predict the long-term effects (100 years) of BBFs and derived blends on soil C sequestration.
Results indicate that biochar exhibits outstanding high stability and effectiveness in promoting soil carbon sequestration, even when mixed with more degradable BBFs. In contrast, more degradable components within the blends (such as insect and microbial biomass) enhance CO2 emissions, suggesting a need for strategic selection of BBFs and their blends to optimise soil carbon retention and minimise negative climate impacts. This research underscores the importance of integrating experimental data with robust modelling frameworks to better predict the long-term environmental outcomes of agricultural practices.
In conclusion, our study provides insights into the complex dynamics of EOM pool decomposition of novel BBFs, offering a comprehensive understanding of both their short-term impacts and long-term implications. This knowledge provides practical guidelines for agricultural practitioners and policymakers aiming to enhance soil carbon sequestration, reduce greenhouse gas emissions, and improve soil health.
Researchers will learn how to apply integrated experimental and modelling methods to assess the environmental benefits and risks of different fertiliser options. By leveraging these insights, stakeholders can enhance their strategies for sustainable soil management and contribute to climate change mitigation efforts within their own practices.
