Investigating the role of minerals in soil organic matter dynamics


Soil organic matter is the largest contributor to soil health in soils, especially in the highly weathered soils in Georgia that lack the less-weathered (2:1 layer) clays of the upper mid-west. Maintaining and increasing the organic matter content of our soils is essential for retaining and supplying nutrients and water to agricultural crops and forests and increasing beneficial microbial activity. However, all soil organic matter is not the same. Organic matter that is stuck on or within minerals or trapped inside mineral micro-aggregates stays around much longer than organic matter that is free. Increasing these mineral associated organic matter (MAOM) forms is the key to maintaining higher organic matter in soils.


The mechanisms and processes that control the amount of mineral associated organic matter are under dispute and thus we cannot currently advise farmers and landmanagers on the best amendments or practices to increase MAOM in their soils. Our research group focuses on unraveling these mechanisms through a focus on iron minerals and iron cycling in soils.


Our group has done primary research and organized meta-analysis working groups (which analyze prior published work) on the controls of organic matter content in soils. Our primary research leverages NSF funding from a soil iron cycling grant and two Critical Zone Observatory grants, one just over the border in South Carolina and one in Puerto Rico, that focus on how iron dynamics in soil impacts organic matter. Our students and postdocs have focused research on the role of iron in generating or destroying mineral associated organic matter. In addition, using NIFA funding, we organized an extension of a Powell Center Working Group to facilitate the production of the International Soil Radiocarbon Database (ISRad) that compiles and makes assessable data from hundreds of published studies on the age of soil organic matter (


Our primary research on mineral associated organic matter has shown that the complexities of soil iron cycling can both generate or destroy MAOM depending on the conditions. For instance, recently formed iron-MAOM is highly susceptible to destruction if soils become excessively wet and low oxygen conditions occur. Conversely, if the soil is kept oxygenated, these iron-MAOM are extremely well protected from microbial decomposition. Our primary research work has generated new theories of soil organic matter behavior and influenced how organic matter is represented in global carbon cycling models. Similarly, the International Soil Radiocarbon Database that our working group is now being used by researchers around the world to test ideas of soil organic matter processes using big data.

State Issue

Sustainability, Conservation, and the Environment


  • Year: 2020
  • Geographic Scope: International
  • County: Clarke
  • Location: College Station, Athens
  • Program Areas:
    • Agriculture & Natural Resources


    Thompson, Aaron


CAES Collaborator(s)

  • Mantripragada, Nehru S.

Non-CAES Collaborator(s)

  • Christof Meile
  • Dan Markewitz
  • Paul Schroeder
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Research Impact