SREL Reprint #2102





The Microbial Activity Season in Southeastern Hydric Soils

J. P. Megonigal, S. P. Faulkner, and W. H. Patrick

The growing season requirement is an often overlooked part of the definition for hydric soils. The current technical definition for a hydric soil states that flooding or soil saturation must occur during the portion of the year when soil temperature at 50 cm is >5ºC. In this study, we defined the portion of year when soils were >5ºC at 50 cm as the microbial activity season and reserved the term growing season for plant activity. In the technical criteria for hydric soils, specific microbial activity season months have been assigned to each of the soil temperature regimes. Our objectives were to determine the portion of the year when southeastern U.S. hydric soils are <5ºC at 50 cm and to estimate rates of microbial activity during winter flooding. We found that 34 bottomland hardwood forest soils in South Carolina, Louisiana, and Mississippi were never <5ºC at 50 cm during a period of 2 to 3 yr. Also, winter rates of soil respiration and 02 consumption (1.6 mL 02 L-1 air d-1) are apparently sufficient to cause anoxia in saturated soils. Based on the available data, we recommend a 12-mo microbial activity season for southeastern bottomland hardwood forests. Additional data will be necessary to determine the relationships between temperature, soil saturation, and development of redoximorphic features in southeastern soils.

SREL Reprint #2102

Megonigal, J.P., S.P. Faulkner, and W.H. Patrick, Jr. 1996. The microbial activity season in southeastern hydric soils. Soil Science Society of America Journal 60:1263-1266.

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