Exploring the Role of Arbuscular Mycorrhizal Fungi in Carbon Sequestration in Agricultural Soil, Part III [GRACEnet].

Sequestering carbon in agricultural soils can help mitigate increases in atmospheric CO₂.  Work at Rodale Institute’s Farming Systems Trial indicates significant potential for carbon sequestration in organically farmed soils.  A potential mechanism for this is C storage in the arbuscular mycorrhizal [AM] fungus produced glycoprotein glomalin, a compound that plays a role in stabilizing soil aggregates and is resistant to degradation.  A three year study was initiated in 2006 utilizing three farming systems: conventional, organic with animal manure addition, and organic with legume cover crops.  Soil samples were collected to a depth of 80 cm on Nov. 29, 2006, Nov. 1, 2007, and Dec. 3, 2008 following corn (Zea mays) harvests.  Samples were segmented by soil profile depth and analyzed for AM fungi, glomalin, soil C and organic matter, and water stable soil aggregates.  Bulk density for each FS x depth combination was determined on the 2007 and 2008 samples.  The organic rotations had more propagules of AM fungi in the top 20 cm of soil than the conventional rotation.  Propagules were nearly absent at the 60-80 cm depth in all systems.  Soil carbon in the top 20 cm was significantly greater in the manure (2.59%) and legume (2.41%) based organic systems than in the conventional system (1.79%), but was similar in all systems below that depth.  The organic systems tended to sequester more carbon through the 30 cm depth than the conventional, with sequestration below 30 cm equal among the three systems.  Carbon sequestration in the legume and manure organic systems averaged 367 and 460 kg ha^-1 yr^-1 more, respectively, than that in the conventional through 2007.  Glomalin data will be presented and its contribution to carbon sequestration quantified.