Digestate biofertilization: a sustainable pathway to increase global soil C content

Purpose: This paper is aimed at the determination of digestate potential in a long-term carbon accumulation after its application as a biofertilizer. Method: Literature survey of > 1000 papers was conducted and resulted in a selection of 21 papers that involved data of soil C accumulation after digestate addition for at least a period of 12 months. Meta-analysis was used for data analysis and interpretation of a large database. The results of incorporation of total organic carbon in the soil after digestate biofertilization were measured by one-way analysis of variance (ANOVA). Results: A comprehensive literature review showed trends for carbon increase in the soil for different experiment periods up to 84 months and initial content of carbon in the soil. It was demonstrated that application of digestate, a byproduct of anaerobic digestion, to agricultural soils resulted in an increase of soil carbon content for a period of up to 8 years. Specifically, digestate derived from cow and pig manure had the highest potential to enhance soil carbon accumulation compared to digestate from other organic residues including food waste and sewage sludge, highlighting the need for a proper choice of the waste substrate used in anaerobic digestion. Soil carbon accumulation is notably more pronounced when digestate is applied to soils with low organic matter content, particularly sandy and loam soils. Conclusion: While digestate application to soils is typically used to substitute mineral fertilizers, it also leads to an overall increase in soil carbon content. Research Highlights • Among different types of manure cow and pig manure showed the highest results in the terms of long term (> 12 months) carbon accumulation in the soil after biofertilization. • A general tendency of lower carbon increase in the soil for the period of 12 months and maximum increase at 36 months of experiment was found. • Digestate can be very successfully used to help reforestation efforts, as they usually have lower soil C content than natural areas. • Obtained results for the period of more than 12 months showed the highest soil carbon increase (more than 2% per month) for sandy soil. • Wheat and maize were found to be the best crops in terms of the potential for carbon accumulation in the soil after digestate biofertilization.