Description:    The potential for climatic factors as well as soil–plant–climate interactions to change as a result of rising levels of atmospheric CO 2 concentration is an issue of increasing international environmental concern. Agricultural and forest practices and managements may be important contributors to mitigating elevated atmospheric CO 2 concentrations. A computer model was developed using the Structural Thinking and Experiential Learning Laboratory with Animation (STELLA) software for soil CO 2 emissions from a short-rotation woody crop as affected by soil water and temperature regimes, root and microbial respiration, and surficial processes such as rainfall, irrigation, and evapotranspiration. The resulting model was validated with good agreement between the model predictions and the experimental measurements prior to its applications. Two scenarios were then chosen to estimate both diurnal and annual soil CO 2 emissions from a 1-ha mature cottonwood plantation as affected by soil temperature, soil (i.e., root and microbial) respiration, and irrigation. The simulation resulted in typical diurnal soil respiration and CO 2 emission patterns, with increases from morning to early afternoon and decreases from early afternoon to midnight. This pattern was driven by diurnal soil temperature variations, indicating that soil temperature was the main influence on soil respiration and CO 2 efflux into the atmosphere. Our simulations further revealed that the average seasonal soil respiration rate in summer was 1.6 times larger than in winter, whereas the average seasonal CO 2 emission rate in summer was 1.77 times larger than in winter. Characteristic annual variation patterns for soil respiration and CO 2 emission also were modeled, with both increasing from January 1 through June 30 followed by steady declines from September 1 through December 31. These results suggest that the STELLA model developed is a useful tool for estimating soil CO 2 emission from a short-rotation woody crop plantation. Content Type Journal Article Pages 1-12 DOI 10.1007/s11270-012-1392-1 Authors Ying Ouyang, USDA Forest Service, Center for Bottomland Hardwoods Research, 100 Stone Blvd., Thompson Hall, Room 309, Mississippi State, MS 39762, USA Theodor D. Leininger, USDA Forest Service, Center for Bottomland Hardwoods Research, 432 Stoneville Road, Stoneville, MS 38776, USA Jeff Hatten, Department of Forestry, Mississippi State University, Mississippi State, MS 39762, USA Prem B. Parajuli, Department of Agricultural and Biological Engineering, Mississippi State University, Mississippi State, MS 39762, USA Journal Water, Air, & Soil Pollution Online ISSN 1573-2932 Print ISSN 0049-6979 Journal Volume Volume 224 Journal Issue Volume 224, Number 1