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United States Department of Agriculture

Agricultural Research Service

Title: Microbial Activity in Response to Water-Filled Pore Space of Variable-Eroded Southern Piedmont Soils

Author
item Franzluebbers, Alan

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 24, 1998
Publication Date: N/A

Interpretive Summary: Potential carbon and nitrogen mineralization and soil microbial biomass carbon are soil biological properties important in understanding nutrient and organic matter dynamics. These soil biological properties are sensitive to soil moisture. The objective of this study was to examine whether adjustment of soil water content to a common level of water-filled pore space might be a simpler, yet acceptable alternative to the more traditional adjustment of water content based on matric potential. The levels of water-filled pore space to achieve maximum activity and biomass under naturally-settled conditions were unaffected by clay content and occurred at 42% for net nitrogen mineralization, 51% for specific respiratory activity of the biomass, 60% for cumulative carbon mineralization, and 76% WFPS for soil microbial biomass carbon. Selecting a common water-filled pore space level of 50% WFPS resulted in 96, 97, 97, and 88% of maximum for these four properties, respectively, and was a reasonable compromise when attempting to estimate these properties during simultaneous incubations. Adjusting soil water content based on WFPS was simpler and nearly as reliable as based on matric potential, in which soil water content at -33 kPa varied from 16-30% (w/v).

Technical Abstract: Potential C and N mineralization and soil microbial biomass C (SMBC) are soil biological properties important in understanding nutrient and organic matter dynamics. The objective of this study was to examine whether adjustment of soil water content to a common level of water-filled pore space (WFPS) may be an acceptable alternative that would require little prior analysis in comparison with adjustment based on matric potential. Potential C and N mineralization and SMBC were determined from 15 variably-eroded soils of the Madison-Cecil-Pacolet association (clayey, kaolinitic, thermic Typic Kanhapludults) in response to WFPS. The levels of WFPS to achieve maximum activity and biomass under naturally-settled conditions were unaffected by clay content and occurred at 42% WFPS for net N mineralization, 51% WFPS for specific respiratory activity of SMBC, 60% WFPS for cumulative C mineralization, and 76% WFPS for SMBC. Selecting a common WFPS level of 50% WFPS resulted in 96, 97, 97, and 88% of maximum for these four properties, respectively. Adjusting soil water content based on WFPS was simpler and nearly as reliable as based on matric potential, in which soil water content at -33 kPa varied from 16-30% (w/v).

Last Modified: 4/19/2014
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