|Martins, Bruno Henrique|
Submitted to: International Humic Substances Society Conference
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2013
Publication Date: 10/14/2014
Citation: Martins, B., Cavigelli, M.A., Maul, J.E., Buyer, J.S., Le, A.N., Rasmann, C., Martin-Neto, L. 2014. Spectroscopic characterization and evaluation of SOM in areas under different soil tillage systems. 10th Meeting of the Brazilian Chapter of the International Humic Substances Society Conference, October 14-18, 2013, Santo Antonio de Goias, Goias State. p. 69-72. Interpretive Summary: Storing carbon in agricultural soils can help reduce the atmospheric concentration of carbon dioxide, the dominant greenhouse gas. The amount, form, and recalcitrance to decomposition of soil carbon are influenced by agricultural management. It is largely unknown how organic farming systems impact these aspects of soil carbon storage. We showed, at the long-term Beltsville Farming Systems Project, that soil organic carbon is greater by about 11 to 18% in organically managed soils than in soils managed using conventional methods. We found that in organic systems the amount of occluded particulate organic matter, a form of soil carbon that is relatively recalcitrant, was about 30% greater than in the conventional systems. Using spectroscopic characterization we found that the chemical makeup of the occluded particulate organic matter was more complex in the organic than the conventional systems. These results suggest that organic farming may have increased the stability of the carbon in the soil. This information will be useful to other scientists and eventually to policymakers interested in identifying best management practices to augment storage of organic carbon in agricultural soils.
Technical Abstract: Agricultural management influences the amount of carbon returned to the soil in the form of plant residues and animal manures and the rate of decomposition of soil carbon. The physical and chemical characteristics of soil carbon influence its recalcitrance to decomposition. We sampled soil from the five cropping systems at the long-term Beltsville Farming Systems Project to evaluate levels of soil organic carbon and to better understand mechanisms of soil carbon sequestration in these soils. We measured free and particulate organic matter (fPOM and oPOM, respectively) carbon fractions and characterized the chemical structure of fPOM and oPOM using pyrolysis gas chromatography/mass spectrometry (pyr GC/MS). We found that soil organic carbon is greater by about 11 to 18% in organically managed soils than in soils managed using conventional methods. Free POM was greater by about 85% in organic than conventional systems. Occluded POM was about 30% greater in the organic than the conventional systems. The spectroscopic characterizations showed that there were more recalcitrant compounds (furan and polysaccharide derivatives, aromatic lignin derivatives, lipids with ketone structures) in the organic than the conventional systems. These results suggest that the organic carbon in the organic systems is more recalcitrant to decomposition than that in the conventional systems. These differences may be due to poultry litter applications and legume cover crops in organic systems that are not part of the conventional systems. Further investigation of these linkages will help improve our understanding of mechanisms involved in carbon sequestration in agricultural soils.