The study analyzed the organic molecular marker signatures in a maize cultivated Fluvisol ameliorated with 5 and 10 t.ha−1 biochar at the experimental field of the ISSAPP N. Poushkarov institute in Bulgaria. The n-alkane signatures and the carbon preference index (CPI) in the biochar treated soils revealed that sources of SOM were predominantly of microbial/thermal origin, while the source was only thermal in the pure biochar sample, (CPIodd/even0.84). There was evidence from the molecular marker analysis that biochar addition may initially bring improvement of soil microbiological status. There was no significant co-occurrence of polycyclic aromatic hydrocarbons released from biochar several months after incorporation in the soil.

Biochar is widely used as a soil amendment to improve soil properties and as a tool to absorb net carbon from the atmosphere. In this study we determined the signatures of organic molecular markers in soil following the incorporation of 5 and 10 t/ha biochar in a Fluvisol, cultivated with maize at the experimental field of the ISSAPP “N. Poushkarov” institute in Bulgaria. The n-alkane distribution in the biochar treated soils was uni- or bimodal maximizing at n-C17 alkane, n-C18 or C18 branched alkanes, i.e. there was an imprint of biomass burning, e.g. from the biochar due to predominance of short chain (< C20) homologues and increased microbial activity (presence of branched alkanes). This is also confirmed by the values for the average chain length (ACL) of n-alkanes which indicated prevalence of homologues of shorter chain (20–21 C atoms) in the variants of longer biochar residence time. There was evidence of trans-13-docosenamide, which originated from biochar. Fatty acids and fatty alcohols distributions also implicate microbial contribution to soil organic matter (SOM), supporting the suggestion that biochar addition can improve soil microbiological status.

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Three types of organic ameliorants, sheep manure, sewage sludge from a waste water treatment plant and a plant compost were added to an Alluvialmeadow soil (Fluvisol). There was evidence for well-preserved biomarker signals and higher values of the carbon preference index (CPI) in the sludge and manure-treated soils, while lower values, typical of microbial alkanes, indicating a high degree of degradation were observed in the plant compost amended soil. Sludge and sheep manure originating metabolic products, such as steroids and polycyclic aromatic hydrocarbons (PAHs) have been preserved in the Fluvisol after 104 days of composting.

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