Carbon dioxide emissions from biochar in soil: role of clay, microorganisms and carbonates

Abstract

Summary The stability of biochar in soil is of importance if it is to be used for carbon sequestration and long‐term improvement of soil properties. It is well known that a significant fraction of biochar is highly stable in soil, but carbon dioxide (CO2) is also released immediately after application. This study investigated the nature of the early release of CO2 and the degree to which stabilizing mechanisms protect biochar from microbial attack. Incubations of 14C‐labelled biochar produced at different temperatures were performed in soils with different clay contents and in sterilized and non‐sterilized soils. It emerged that carbonate may be concentrated or form during or after biochar production, resulting in significant carbonate contents. If CO2 released from carbonates in short‐term experiments is misinterpreted as mineralization of biochar, the impact of this process may be significantly over‐estimated. In addition to the CO2 released from carbonates, there appears to be a labile fraction of biochar that is oxidized quickly during the first days of incubation, probably by both abiotic and biotic processes. Later in the incubation, biotic mineralization appears to be the primary cause of CO2 evolution. Finally, we found that both production temperature and clay content affect biochar mineralization. As protective mechanisms hypothesized to prevent degradation of organic matter in soil usually implicate clay, we conclude that biochar is likely to be protected from mineralization during the early stages of incubation by its own recalcitrant chemical and physical nature as well as by physical protective mechanisms.

The capacity of biochar made from common reeds to neutralise pH and remove dissolved metals in acid drainage

“…We also identified calcite by XRD in the biochar (Fig. 5, pre-acid treatment only) which is consistent with previous research (Yuan et al 2011b;Bruun et al 2014). It is likely protons (H + ) in the acid drainage dissolve solid phase carbonate/calcite in the biochar to form dissolved alkalinity/HCO 3 − and Ca 2+ in the leachate water (Fig.…”

Use of biochar and oxidized lignite for reconstructing functioning agronomic topsoil: Effects on soil properties in a greenhouse study

“…Other studies have examined the interactive priming effects (i.e., stimulation or suppression of C mineralization) of LOM and recalcitrant C applied to soil simultaneously (Hamer et al 2004;Liang et al 2010;Keith et al 2011;Rogovska et al 2011;Zavalloni et al 2011). Results were contradictory and may relate to the different soil characteristics, variable biochar feedstock, production conditions, and study durations used in these studies (Zimmerman et al 2011;Bruun et al 2014). For example, reported no or small mineralization of pecan-shell biochar (7008C) in the presence of fresh LOM (switchgrass residue), whereas the presence of the biochar enhanced the mineralization of the added fresh LOM.…”

Effects of biochar on the acidity of a loamy clay soil under different incubation conditions

“…3 Dynamics of soil pH of all treatments during a period of 68-day, in which each value represents the mean of three replicates with the standard error shown by the vertical bars Each value is the mean of three replicates with the standard deviation, and values marked with the same letters in soil-PB or soil-PT treatment are not significantly different (P>0.05) a PBV soil+PB (ventilated incubation), PBS soil+PB (sealed incubation), PTV soil+PT (ventilated incubation), PTS soil+PT (sealed incubation), CKV soil only (ventilated incubation), CKS soil only (sealed incubation) b Δ pH means pH increment in soil-biochar treatments compared to the controls incubated under the same conditions biochars, especially carbonate in PB, can ameliorate soil acidity to some extent through a neutralization reaction (Table 2 and Figs. 1 and 2) (Bruun et al 2014); and (e) the large surface area and porous property of biochar immobilize ammonium N and then inhibit nitrification (Nelissen et al 2012;Pocknee and Sumner 1997), leading to soil acidity amelioration. This is supported by the negative correlation between pH and nitrate N (r=−0.742, P<0.01, n=18), suggesting that PB and PT could be used as an agent to apply to soils with fertilizer, which then plays a similar role to that of a nitrification inhibitor in soil acidity amendment through nitrification suppression (Mao et al 2010).…”

“…In addition, clay content has an important role in maintaining soil structure, CEC, and other local environmental condition in soils (Bruun et al 2014). A previous study has reported that incubation condition (ventilated and sealed) had few effects on acidification amendment in clayey soils in hilly red soil region of southern China (Zhao et al 2015a).…”