Biochar and Earthworm Effects on Soil Nitrous Oxide and Carbon Dioxide Emissions

Abstract

Biochar is the product of pyrolysis produced from feedstock of biological origin. Due to its aromatic structure and long residence time, biochar may enable long-term carbon sequestration. At the same time, biochar has the potential to improve soil fertility and reduce greenhouse gas (GHG) emissions from soils. However, the effect of biochar application on GHG fluxes from soil must be investigated before recommendations for field-scale biochar application can be made. A laboratory experiment was designed to measure carbon dioxide (CO) and nitrous oxide (NO) emissions from two Irish soils with the addition of two different biochars, along with endogeic (soil-feeding) earthworms and ammonium sulfate, to assist in the overall evaluation of biochar as a GHG-mitigation tool. A significant reduction in NO emissions was observed from both low and high organic matter soils when biochars were applied at rates of 4% (w/w). Earthworms significantly increased NO fluxes in low and high organic matter soils more than 12.6-fold and 7.8-fold, respectively. The large increase in soil NO emissions in the presence of earthworms was significantly reduced by the addition of both biochars. biochar reduced the large earthworm emissions by 91 and 95% in the low organic matter soil and by 56 and 61% in the high organic matter soil (with and without N fertilization), respectively. With peanut hull biochar, the earthworm emissions reduction was 80 and 70% in the low organic matter soil, and only 20 and 10% in the high organic matter soil (with and without N fertilization), respectively. In high organic matter soil, both biochars reduced CO efflux in the absence of earthworms. However, soil CO efflux increased when peanut hull biochar was applied in the presence of earthworms. This study demonstrated that biochar can potentially reduce earthworm-enhanced soil NO and CO emissions. Hence, biochar application combined with endogeic earthworm activity did not reveal unknown risks for GHG emissions at the pot scale, but field-scale experiments are required to confirm this.

Linking N2O emissions from biochar-amended soil to the structure and function of the N-cycling microbial community

“…As NH 4 þ , NO 3 À and DOC concentrations decreased N 2 O fluxes declined in all microcosms because electron donors and acceptors for microbial N 2 O formation became limiting. The significantly lower N 2 O emissions from biochar-containing microcosms observed within the first week (Figure 1b, Supplementary Figure S2b) agree with the findings of several recently published field-and laboratory-based studies using different biochars and soils (Yanai et al, 2007;Singh et al, 2010b;van Zwieten et al, 2010;Taghizadeh-Toosi et al, 2011;Wang et al, 2011b;Augustenborg et al, 2012;Wang et al, 2012;Zheng et al, 2012;Zhang et al, 2012a, b). According to these studies, the most important environmental factors responsible for the reduced N 2 O emissions from biochar-amended soil were: (i) limited bioavailability of electron donors and acceptors (DOC,NO 3 À and NH 4 þ ) for microbial nitrification and denitrification due to sorption/ immobilization onto biochar particles (Singh et al, 2010b;Taghizadeh-Toosi et al, 2011;Wang et al, 2011a); (ii) improved soil aeration through biochar addition and consequently reduced denitrification (Yanai et al, 2007;van Zwieten et al, 2010;Augustenborg et al, 2012;Zhang et al, 2012b); and (iii) increased activity of N 2 O-reducing bacteria due to an elevated soil pH caused by biochar addition (van Zwieten et al, 2010;Zheng et al, 2012).…”

Combined effects of nitrogen deposition and biochar application on emissions of N2O, CO2and NH3from agricultural and forest soils

“…N 2 O, CO 2 and NH 3 emissions affected by biochar addition Biochar addition significantly decreased N 2 O emission in agricultural soil under the N120 treatment and in forest soil under both N60 and N120 treatments (Table 3), which is in accordance with the results of Augustenborg et al (2011), Singh et al (2010 and Wang et al (2011). Three possible explanations may apply.…”

“…Moreover, biochar amendment may reduce CO 2 emissions due to the fact that biochar may increase microbial biomass in soil by the complexation of SOM with biochar particles, and yet simultaneously induce negative priming of native soil C mineralization (Liang et al 2010). As for the agricultural soil, biochar incorporation increased CO 2 emissions at the rate of 0 kg N ha −1 yr −1 (Table 3), which was in agreement with Augustenborg et al (2011) that CO 2 emissions increased in the low-SOM soil. Generally due to the priming effect, biochar incorporation may stimulate soil microorganisms to decompose SOM (Bünemann et al 2006;Smith et al 2010;Nelissen et al 2012) and provide readily available substrate for denitrifying microorganisms (Blagodatskaya and Kuzyakov 2008;Ameloot et al 2013) and mineralize the labile biochar C fraction by biotic or abiotic ways (Kolb et al 2009;Zimmerman et al 2011) in agricultural soil thus enhance CO 2 emissions.…”

“…The forest soil emitted more CO 2 than the agricultural soil (Table 3), possibly due to the soil's intrinsic SOM and dissolved organic C content, which has been demonstrated by previous studies where cumulative CO 2 fluxes, soil SOM and dissolved organic C were significantly positively correlated (Augustenborg et al 2011;Wang et al 2011). In contrast to agricultural soil, adding biochar significantly decreased the average CO 2 emissions over all treatments from the forest soil (Table 2), which may be explained by the relatively higher SOM in forest soil (Table 1).…”

Impact of earthworm <i>Lumbricus terrestris</i> living sites on the greenhouse gas balance of no-till arable soil

“…Most of the investigations of earthworm effects on GHG emissions have been carried out in the laboratory Rizhiya et al, 2007;Giannopoulos et al, 2010;Lubbers et al, 2011;Augustenborg et al, 2012) and to our knowledge, only three field experiments have been conducted (Borken et al, 2000;Amador and Avizinis, 2013;Lubbers et al, 2013b). Recent reviews have underlined the need for field studies with all major gases (N 2 O, CO 2 and CH 4 ) to provide a more comprehensive picture of earthworm contribution to soil GHG emissions (Lubbers et al, 2013a;Blouin et al, 2013).…”