Increased CO₂ fluxes from a sandy Cambisol under agricultural use in the Wendland region, Northern Germany, three years after biochar substrates application

Abstract

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 d 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.

Impact of biochar on nutrient supply, crop yield and microbial respiration on sandy soils of northern Germany

“…No biochar effects on CO 2 fluxes were found in previous field experiments using relatively low biochar application rates (< 10 t ha −1 ) (Karhu, Mattila, Bergström, & Regina, 2011;Mechler, Jiang, Silverthorn, & Oelbermann, 2018;Sackett et al, 2015), which is confirmed by the results from the B and D:BL treatments in the current field experiments. Also, Polifka, Wiedner, and Glaser (2018) found no significant increase of mean CO 2 fluxes from heterotrophic respiration when they applied a mixture of biogas plant digestates and biochar on a Cambisol in northern Germany at low biochar application rates (3 t ha −1 ). In contrast, when applying high biochar application rates (40 t ha −1 ), a strong (53%) and significant increase of CO 2 fluxes was found (Polifka et al, 2018).…”

“…Also, Polifka, Wiedner, and Glaser (2018) found no significant increase of mean CO 2 fluxes from heterotrophic respiration when they applied a mixture of biogas plant digestates and biochar on a Cambisol in northern Germany at low biochar application rates (3 t ha −1 ). In contrast, when applying high biochar application rates (40 t ha −1 ), a strong (53%) and significant increase of CO 2 fluxes was found (Polifka et al, 2018). However, the increased CO 2 fluxes only accounted for about 0.3% of the added biochar, indicating a substantial sequestration of carbon after biochar application.…”

“…Although incubation studies applied 13 C-or 14 C-labelled material to identify CO 2 fluxes from biochar carbon (Kuzyakov et al, 2009;Pan, Li, Chapman, Khan, & Yao, 2016), field experiments with labelled biochar were not conducted, and the unequivocal identification of the source of the additional CO 2 is not possible. The increasing CO 2 fluxes were assigned to the microbial decomposition of a labile organic matter fraction of the applied biochar (Castaldi et al, 2011) but also to organic matter decomposition of organic fertilizers applied together with the biochar (Polifka et al, 2018). Another possibility is the contribution of respired plant carbon (Fang et al, 2016;Major, Lehmann, Rondon, & Goodale, 2010).…”

Effect of biochar fertilizers on amino acid variability of Secale cereale and Lupinus angustifolius

“…Plant-available nitrogen during winter rye growing season seems to be lower for the digestate, fermented digestate and compost treatments reflected in reduced nitrogen uptake. However, it should be noted that, albeit not significant, high biochar application rates increased the average nitrogen uptake in three fertilizer groups, which could be probably explained by increased cation exchange capacity as shown by Glaser et al (2015) or due to a higher mineralization rate through an increased microbial activity favored by the high porosity of biochar (Thies and Rillig 2009;Lehmann et al 2011;Polifka et al 2018). Due to its biological nitrogen fixation (BNF) properties, lupine holds a special position within this field experiment and the results are difficult to compare with maize and winter rye grown in two previous years of this experiment.…”

The effect of biochar with biogas digestate or mineral fertilizer on fertility, aggregation and organic carbon content of a sandy soil: Results of a temperate field experiment

“…Of the ten total treatments established in 2012 ( Glaser et al., ; Polifka et al., ), six treatments were analyzed in the present experiment, including two fertilizer treatments [mineral fertilizer (M) or biogas digestate (D)] applied without biochar (B0), with 3 Mg biochar ha −1 (B3), or with 40 Mg biochar ha −1 (B40). The remaining four treatments ( i.e ., compost with and without 10 Mg biochar ha −1 and fermented biogas digestate with and without 40 biochar ha −1 ) were excluded due to an unbalanced experimental design ( i.e ., they did not feature the biochar levels 0, 3, and 40 Mg ha −1 which were applied with the other six treatments) and they did not receive consistent fertilizer application ( i.e ., all received biogas digestate as fertilizer after 2012).…”