Impact of Biochar Organic and Inorganic Carbon on Soil CO2 and N2O Emissions

Abstract

Biochar has been shown to influence soil CO and NO emissions following application to soil, but the presence of carbonates in biochars has largely confounded efforts to differentiate among labile and recalcitrant C pools in biochar and establish their timeframe of influence. Understanding the mechanism, magnitude, and duration of biochar C pools' influence on C and N dynamics is imperative to successful implementation of biochar for C sequestration. Here we therefore aim to assess biochar organic and inorganic C pool impacts on CO and NO emissions from soil amended with two untreated biochars, inorganic carbon (as NaCO), acid (HCl) and bicarbonate (NaHCO) extracts of the biochars, and acid and bicarbonate/acid-washed biochars during a 140-d soil incubation. We hypothesized that (i) both biochar labile organic carbon (LOC) and inorganic carbon (IC) pools contribute significantly to short-term (<1 mo) CO emissions from biochar-amended soil, (ii) biochars will influence the size of soil NH and NO pools, and (iii) changes in soil inorganic N pools will affect soil NO emissions. All biochar, biochar extract, and carbonate treatments (12 total) increased CO produced during the initial ≤48 h of the incubation relative to controls, indicating that both biochar LOC and IC contribute to CO emissions. Of these treatments, only bicarbonate extracts of the biochars increased total C losses significantly. However, treatment impacts on soil NO production were not significant despite significant effects of select treatments on inorganic N pools. Overall, results indicate that biochars contain small LOC and IC pools that are stabilized by a larger recalcitrant organic C pool.