|Parkin, Timothy - Tim|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/7/2010
Publication Date: N/A
Citation: Interpretive Summary: Addition of biochar (a.k.a. charcoal) to agricultural soils has been proposed as a means of reducing the net emissions of greenhouse gases from agricultural soils. Previous research has shown that the half-life of biochar carbon in soils is approximately 1,000 years and hence soil biochar additions appear to be highly effective means of sequestering carbon. Other researchers, however, have suggested that biochar may accelerate the decomposition of soil organic matter and thereby increase the rate of carbon dioxide emission form soils. The balance between these two processes is not known, furthermore the effect of biochar on the stabilization of carbon in organic residues is not known. During a 500-day incubation study, we did not detect any loss of biochar carbon; however biochar additions increased carbon dioxide emissions, indicating accelerated decomposition of soil organic matter. The amount of additional carbon dioxide carbon lost was 18 to 23% of the amount of biochar carbon added to the soils. A substantial interaction between biochar and manure was also observed indicated that biochar either helped stabilize manure carbon or the presence of manure reduced the effect of biochar on the decomposition of soil organic matter. This study will help scientist to better understand how biochar influences soil processes and will help both policy makers and regulators to develop and administer effective policies for reducing green house gases emissions from agricultural soils.
Technical Abstract: Previous studies indicate that biochar additions sometimes increase soil respiration and carbon dioxide emissions, which could partially offset carbon (C) credits associated with soil biochar applications. Little is known, however, about the impact of biochar on the mineralization of manure in soil systems and how interactions between biochar and manure impact C sequestration and greenhouse gas emissions from soils. We studied the effect of biochar and dried swine manure additions on changes in bulk density, total soil organic carbon (SOC) and emissions of nitrous oxide (N2O) and carbon dioxide (CO2) during a 500-day soil column incubation study. Mass balance analysis indicated biochar C recoveries ranging from 98 to 108% suggesting that little biochar C was mineralized during the incubation. Biochar additions reduced N2O emissions measured once near the end of the incubation. The N2O emissions were weakly correlated with soil bulk density, suggesting that enhanced soil aeration contributed to the reductions in N2O emissions. Biochar additions consistently increased CO2 emissions (measured 13 times during the incubation) relative to no-biochar controls with cumulative CO2-C loss equivalent to 18-23% of biochar C applied. However, a distinct biochar-by-manure interaction for CO2 flux indicated that biochar either helped stabilize manure C or the presence of manure reduced the effect of biochar on the mineralization of SOC. For the studied system, we conclude that biochar additions sequestered large amounts of highly stable C, reduced N2O emissions, increased CO2 emissions from the soils, and reduced rates of CO2 emissions following a manure addition.