Tracking C and N dynamics and stabilization in soil amended with wheat residue and its corresponding bioethanol by‐product: a ¹³C/¹⁵N study

Abstract

Removing agricultural cellulosic residues from fields for the production of 'second generation biofuels'has the potential to profoundly alter C and N cycling in soil, increasing the risk of soil organic matter depletion and favoring soil-atmosphere gaseous exchanges. However, these negative impacts could potentially be offset by amending the soil with the solid by-product which is generated during bioethanol production. In a 100 days laboratory study, we investigated the fate of C and N after soil amendment with doubly labeled ( 13 C, 15 N) wheat residue (WR) and the corresponding bioethanol by-product (i.e. nonfermentable wheat residue NFWR) with and without extra N addition. Substituting WR with the corresponding amount of recovered bioethanol by-product partially compensated the C losses of full crop residue removal. When the equivalent amount of C was added as WR and NFWR, NFWR-derived C was found in significantly higher proportion in macroaggregates in soil (17.0 vs. 8.9%) after 100 days. Addition of both WR and NFWR reduced soil organic C (SOC) mineralization, i.e. it caused a negative priming effect in soil. However, this pattern was reversed when extra N was added. Both WR and NFWR increased the proportion of soil water-stable macroaggregates from 16% (in control) to 20-24% (in the different treatments). The results suggest that the more recalcitrant compounds derived from bioethanol production may stabilize more strongly and persist within the protected fractions of SOM pools. Our study demonstrates that NFWR, compared with WR application, neither increased N 2 O emissions nor had a negative impact on aggregate formation in the midterm. This demonstrates that NFWR has potential for replenishing SOC stocks.

Effect of crop residue incorporation on soil organic carbon and greenhouse gas emissions in European agricultural soils

“…Those authors explained the difference by the smaller size and subsequent increase of surface area of the crop residues in the laboratory experiments compared with field‐scale applications. This applies to laboratory experiments in our analysis (Velthof et al ., ; Garcia‐Ruiz & Baggs, ; Cayuela et al ., ), compared to the field experiments (Baggs et al ., ; Mutegi et al ., ; Abalos et al ., ; Sanz‐Cobena et al ., ). Moreover, under laboratory conditions, moisture and temperature are stable and optimized for microbial activity, thus promoting higher emissions compared to field experiments (Chen et al ., ).…”

The way forward in biochar research: targeting trade‐offs between the potential wins

“…solid by‐products) of bioethanol production in terms of CO 2 and N 2 O emissions (Cayuela et al . ). Also, a smaller quantity of biochar of high stability can have the same C abatement value as a larger quantity of less stable biochar (Crombie et al .…”

“…) via a number of mechanisms (Singh et al . ; Cayuela et al ., , ). For example, biochar addition might change the microbial community including N 2 O‐producing organisms, or alter soil structure and thereby the anaerobic volume of the soil in which denitrification takes place (Van Zwieten et al .…”

“…). Biochar has also been suggested to function as an ‘electron shuttle’ that facilitates the transfer of electrons to denitrifying microorganisms (Cayuela et al ., , ). A last possible mechanism is that biochar could sorb N 2 O sufficiently to suppress emissions (Van Zwieten et al .…”

“…Other potential benefits or ‘wins’ include the suppression of greenhouse gas emission such as N 2 O and CH 4 from soils (Karhu et al . ; Cayuela et al ., , ); the remediation of contaminated soils as biochar strongly binds to most organic pollutants (Cornelissen et al . ); and waste disposal (Cascarosa et al .…”