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ARS Home » Southeast Area » Tifton, Georgia » Southeast Watershed Research » Research » Publications at this Location » Publication #419698
Research Project: Optimizing Crop Management Strategies for Enhancing the Sustainability of Integrated Crop and Livestock Agroecosystems in the Gulf Atlantic Coastal Plain of Georgia

Location: Southeast Watershed Research

Title: Organic matter characteristics and mineralization in ironstone gravel from two Plinthic soils in the Coastal Plain of Georgia

Author
item Pisani, Oliva
item Klick, Sabrina
item Strickland, Timothy

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2025
Publication Date: 4/7/2025
Citation: Pisani, O., Klick, S.A., Strickland, T.C. 2025. Organic matter characteristics and mineralization in ironstone gravel from two Plinthic soils in the Coastal Plain of Georgia. Soil Science Society of America Journal. 89, e70047. https://doi.org/10.1002/saj2.70047.
DOI: https://doi.org/10.1002/saj2.70047

Interpretive Summary: Although agricultural soils can contain significant amounts of rock fragments (> 2 mm), only the fine fraction (< 2 mm) has routinely been included in analyses of soil carbon (C) and nitrogen (N), and in estimations of soil function. In agricultural soils of the southern Coastal Plain, rock fragments are abundant in the form of highly weathered ironstone gravel. The purpose of this study was to perform an incubation experiment using ground and unground ironstone gravel to understand their role in holding soil C and N and making this material available for biological use. Results from this incubation study revealed that ironstone gravel can contain C and N in appreciable amounts. Material inside the ironstone gravel includes inorganic N in the form of nutrients, dissolved organic matter (DOM), and microbial biomass pools. Analysis of the DOM generated from the gravel indicates that this material is relatively fresh and of microbial origin. Both ground and unground gravel can evolve carbon dioxide (CO2) and nitrous oxide (N2O). These results emphasize the importance of including ironstone gravel in estimates of soil C and N.

Technical Abstract: Agricultural soils can contain a significant proportion of rock fragments, but most routine procedures for the estimation of soil carbon (C) and nitrogen (N) stocks promote the exclusion of the >2 mm component. Thus, the purpose of this experiment was to study the role of rock fragments (ironstone gravel) on soil C and N dynamics in two Plinthic soils of the southern Coastal Plain of Georgia. Specifically, the objective of this study was to conduct an incubation experiment using ground and unground ironstone gravel to 1) evaluate their C and N mineralization potential, 2) quantify and characterize the dissolved organic matter (DOM) generated from them, and 3) quantify their greenhouse gas evolution potential. Results from this incubation experiment revealed that ironstone gravel can contain 1-5% of potentially mineralizable C and N, and that both ground and unground gravel can generate CO2 and N2O. The DOM released upon grinding the gravel is relatively fresh and of microbial origin. Disregard of the gravel fraction may result in an underestimation of the soil total C and N, which has implications for the accounting of C in agricultural soils and for the development of strategies to sequester soil C.