Increased CO 2 fluxes from a sandy Cambisol under agricultural use in the Wendland region, Northern Germany, three years after biochar substrates application

• Published in: Global change biology. Bioenergy Vol. 10; no. 7; pp. 432 - 443
• Main Authors: Polifka, Steven, Wiedner, Katja, Glaser, Bruno
• Format: Journal Article
• Language: English
• Published: 01-07-2018
• ISSN: 1757-1693; 1757-1707
• DOI: 10.1111/gcbb.12517

In recent years, biochar has been discussed as an opportunity for carbon sequestration in arable soils. Field experiments under realistic conditions investigating the
CO
2
emission from soil after biochar combined with fertilizer additions are scarce. Therefore, we investigated the
CO
2
emission and its
13
C signature after addition of compost, biogas digestate (originating from C4 feedstock) and mineral fertilizer with and without biochar (0, 3, 10, 40 Mg biochar/ha) to a sandy Cambisol in Northern Germany. Biomass residues were pyrolized at ~650°C to obtain biochar with C3 signature. Gas samples were taken biweekly during the growing season using static chambers three years after biochar substrate addition. The
CO
2
concentration and its δ
13
C isotope signature were measured using a gas chromatograph coupled to an isotope ratio mass spectrometer. Results showed increased
CO
2
emission (30%–60%) when high biochar amount (40 Mg/ha) was applied three years ago together with mineral fertilizer and biogas digestate. On average, 59% of the emitted
CO
2
had a C3 signature (thus, deriving from biochar and/or soil organic matter), independent of the amount of biochar added. In addition, our results clearly demonstrated that only a small amount of released
CO
2
derived from biochar. The results of this field experiment suggest that biochar most likely stimulates microbial activity in soil leading to increased
CO
2
emissions derived from soil organic matter and fertilizers mineralization rather than from biochar. Nevertheless, compared to the amount of carbon added by biochar, additional
CO
2
emission is marginal corroborating the C sequestration potential of biochar.