Monday, November 13, 2006 - 3:30 PM

Soil Respiration in Response to Landscape Position.

Thomas M. DeSutter, USDA-ARS National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011, Timothy Parkin, USDA-ARS-Natl. Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011, United States of America, Thomas Kaspar, USDA/ARS Natl. Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011-4420, Thomas Sauer, National Soil Tilth Lab USDA-ARS, 2150 Pammel Dr., Ames, IA 50011-4420, United States of America, and Jerry L. Hatfield, National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011-4420.

Variations in soil type, due to landscape position, may influence soil respiration.  This study was conducted to determine how landscape position (summit, side-slope, and depression) influences heterotrophic and autotrophic soil respiration. Soil respiration was determined at three landscape positions in a field planted to corn (Zea mays) in central Iowa.  Carbon dioxide concentrations were determined at each landscape position in both root excluded and cropped areas between day of year 153 (June 2) and 180 (June 29) in 2006 using carbon dioxide sensors positioned at the soil surface and at minus 2 cm and minus 10 cm below the soil surface.  In all locations, the carbon dioxide concentrations were about four times greater at the 10 cm depth than at the 2 cm depth at respective landscape positions. The greatest concentration of carbon dioxide (12 mmol mol-1) was observed at the depression site in the cornrow at the 10 cm depth immediately after a rainfall event.  At each landscape position, the concentrations of carbon dioxide at the 2 and 10 cm depths were nearly two times greater in the cornrow compared to the root exclusion zone. Fick’s Law was then used, in conjunction with the diffusivity of carbon dioxide in soil from each landscape position, to estimate the efflux of carbon dioxide. Efflux estimates from the cornrows were about two times greater than from the root exclusion zones at all landscape positions. Also, carbon dioxide efflux was slightly greater from the cornrow at the depression site than any other location and position.