Biochar, a material defined as charred organic matter applied in agriculture, is suggested as a beneficial additive and bulking agent in composting. Biochar addition to the composting feedstock was shown to reduce greenhouse gas emissions and nutrient leaching during the composting process, and to result in a fertilizer and plant growth medium that is superior to non-amended composts. However, the impact of biochar on the quality and carbon speciation of the organic matter in bulk compost has so far not been the focus of systematic analyses, although these parameters are key to determine the long-term stability and carbon sequestration potential of biochar-amended composts in soil. In this study, we used different spectroscopic techniques to compare the organic carbon speciation of manure compost amended with three different biochars. A non-biochar-amended compost served as control. Based on Fourier-transformed infrared (FTIR) and 13C nuclear magnetic resonance (NMR) spectroscopy we did not observe any differences in carbon speciation of the bulk compost independent of biochar type, despite a change in the FTIR absorbance ratio 2925 cm− 1/1034 cm− 1, that is suggested as an indicator for compost maturity. Specific UV absorbance (SUVA) and emission-excitation matrixes (EEM) revealed minor differences in the extractable carbon fractions, which only accounted for ~ 2–3% of total organic carbon. Increased total organic carbon content of biochar-amended composts was only due to the addition of biochar-C and not enhanced preservation of compost feedstock-C. Our results suggest that biochars do not alter the carbon speciation in compost organic matter under conditions optimized for aerobic decomposition of compost feedstock. Considering the effects of biochar on compost nutrient retention, mitigation of greenhouse gas emissions and carbon sequestration, biochar addition during aerobic composting of manure might be an attractive strategy to produce a sustainable, slow release fertilizer.
Bibliographical noteFunding Information:
We thank Ellen Struve, Katharina Mayer and Patricia Riede for their support in the lab, Gerald Buck and Klaus Nickel for freeze-drying, Annette Flicker and Marcus Nowak for access to the FTIR and their support during the measurements, Sabine Flaiz and Peter Kühn for access to the microwave, for their support during aqua regia extractions and for ICP-OES measurements and Wolfgang Gerber for photographs. NH was financially supported by a BMBF PhD scholarship provided by the Rosa Luxemburg Foundation , Berlin, Germany. The composts were produced during a “Short Term Scientific Mission” (STSM) granted to NH by the EU COST Action TD1107 “Biochar as option for sustainable resource management”. We thank Kevin Friedrich and Pyreg GmbH, Dörth, Germany for providing biochar B2. JMR thanks The Spanish Ministry of Economy and Competitiveness (MINECO) for his “Ramón y Cajal” post-doctoral contract (RYC-2014-16338). MINECO is also thanked for the financial support of the projects CGL2015-64811-P and CGL2016-76498-R, which funded the NMR analyses. We thank Cindy Lockwood for valuable comments on the manuscript.
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- Electron exchange capacity
- Farmyard manure
- Humic substances
- Pyrogenic organic carbon
- Sewages sludge char