Saturday, 15 July 2006

Simulated Rainfall Impact on Carbon Dioxide Emissions from Corn and Soybean Cropping Systems on a Mollisol.

Roop Kamal1, Diane E. Stott2, Doug Smith2, and Dennis L. Bucholtz3. (1) Univ of Nebraska, 203 Kiesselbach Crop Research Lab, Dept of Agronomy and Horticulture, Lincoln, NE 68504, (2) USDA-ARS National Soil Erosion Research Laboratory, 275 S Russell St, West Lafayette, IN 47907-2077, (3) USDA-ARS-MWA, National Soil Erosion Research Laboratory, 275 S. Russell Street, West Lafayette, IN 47907

There is an increasing concern for rising GreenHouse Gases (GHGs) in the atmosphere including CO 2. Soil can serve as either a source or a sink for CO2. We have very little information on the impact of rainfall on levels of CO2 emissions from croplands. Objectives of our study were to determine the effects of crop rotation, soil water content, and soil and air temperatures on CO2 flux following simulated rainfall. The experimental site was located in West Lafayette, IN with both corn and soybean rotation crops present after no-till or conventional tillage planting. Carbon dioxide flux was determined using static gas flux chambers and samples were collected before initiation of simulated rainfall and then 0.5, 1, 3, 6, 24, 48, 72 and 96 h after rainfall. Four trials were conducted (May 19, June 22, July 28 and August 20, 2004) during the experimental period. Carbon dioxide flux consistently decreased right after rainfall was applied to the plots. The greatest total CO2 flux during a 96 h experimental period was 2289 g ha-1 h-1 for soybean during Trial 3 when the plants were in the pod-filling stage. The lowest total CO2 flux for soybean was 502 g ha-1 h-1 during Trial 2. For corn, the greatest total CO2 flux was 1207 g ha-1 h-1 for 96 h experimental period during Trial 1, when the plants were in the vegetative growth stage, whereas, the lowest CO2 flux was 418 g ha-1 h-1 for Trial 4. Soybean plots resulted in 370 % and 249 % greater total CO2 flux than corn plots over a 96 h period for Trial 3 and Trial 4, respectively. Previous year's corn residues may have also contributed to the greater CO2 flux observed from soybean plots. No significant differences were observed between CO2 fluxes from corn and soybean for Trial 2. Carbon dioxide flux showed a poor linear regression relationship with soil water content at 12 cm depth for soybean and corn for the four trials with r 2 value of 0.13 and 0.01 respectively. Soil and air temperature did not affect CO2 flux from all the four trials. We suggest that for experiments using static gas flux chambers, gas samples should be taken two to three days after a rainfall event has occurred to capture peak CO2 flux. This information will allow better interpretation of the effects of natural rainfall on GHG experiments with fixed sampling times, and will aid in developing more accurate models of GHG emissions.

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