Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 21, 2009
Publication Date: January 5, 2010
Citation: Novak, J.M., Busscher, W.J., Watts, D.W., Laird, D.A., Ahmedna, M.A., Niandou, M.A.S. 2010. Short-term CO2 mineralization after additions of biochar and switchgrass to a Typic Kandiudult. Geoderma. 154:281-288. Interpretive Summary: The concentration of carbon dioxide in the earth’s atmosphere has been increasing and scientists have been looking for ways to lower its concentration. Soils hold more carbon than the atmosphere, so it is an important storehouse. Storing carbon in southeastern USA Coastal Plain soils is difficult because fresh plant residues are rapidly oxidized by soil microorganisms leaving little behind to improve the soil. Recently, scientists in the USA have focused on applying charcoal as a soil amendment because it was found to improve fertility of unproductive soils in the Amazon basin. However, when carbon is added to soil it can immobilize nitrogen, a critical plant nutrient necessary for high crop yields. Our research examined if charcoal made from pecan shells and incorporated into sandy soils was resistant to breakdown and was able to raise or lower soil carbon and nitrogen levels. Charcoal was laboratory incubated in a southeastern Coastal Plain sandy soil for about 2 months. After this time period, soil carbon and nitrogen were measured and compared to soil without charcoal. We found that adding charcoal and fresh residue raised soil carbon, but also caused lower soil nitrogen levels. The soil nitrogen reduction was temporary; levels later rebounded. Our results showed that adding charcoal to sandy soil improved its carbon content, but that soil nitrogen levels could be temporarily lowered when fresh crop residue is incorporated with it.
Technical Abstract: Biochar was applied to infertile South American soils for millennia to increase fertility and organic carbon (OC) content. Biochar additions to degraded agricultural soil in the southeastern USA Coastal Plain may also increase their fertility and OC status. A laboratory column incubation study was conducted with Norfolk Ap loamy sand (Fine-loamy, kaolinitic, thermic, Typic Kandiudult) mixed with pecan-shell biochar at rates of 0, 0.5, 1.0 and 2.0 % (w/w) and with 0 and 1% (w/w) dried, ground switchgrass (Panicum virgatum). On incubation days 25 and 67, all pots were leached with deionized water and the leachate nitrate (NO3-N), and ammonium (NH4-N) concentrations were measured. Also cumulative soil carbon dioxide (CO2) fluxes after days 25 and 67 were determined. Biochar alone and mixed with soil and switchgrass after 67 days of incubation were characterized for structural modifications using Fourier transformed infrared spectroscopy (FT-IR). Mixing biochar with switchgrass after 67 days caused a significant increase in soil organic carbon content while soil total nitrogen showed mixed results. By days 25 and 67, soil with biochar and switchgrass exhibited higher cumulative CO2 fluxes than in soils without these amendments, implying stimulation of switchgrass mineralization. Significant NO3-N immobilization occurred after 25 days in treatments with biochar + switchgrass. The FT-IR analysis revealed that biochar was mineralized through modification of the aromatic rings to form carbonyl and cyclic ketone-like structures. Biochar application to sandy soil increased the OC content, and was itself fairly resistant to mineralization but stimulated switchgrass mineralization.