Gollany, Hero (USDA-ARS, 48037 Tubbs Ranch Road, Adams, OR, 97810; Phone: 541-278-4410; Fax: 541-278-4372; Email: hero.gollany@oregonstate.edu)

Predicting Carbon Sequestration in Agricultural Soils with the Carbon Balance Model ‘CQESTR’

R.W. Rickman, H.T. Gollany *, S.L. Albrecht, W.W. Wilhelm, R.F. Follett, C.L. Douglas, Jr.

The prospect of storing carbon in soil, as organic matter, provides an opportunity for agriculture to contribute to the reduction of carbon dioxide in the atmosphere. However, a description of management effects on soil organic matter (SOM) is necessary to assess carbon storage in soil. A mathematical model, CQESTR, has been developed to evaluate the changes in SOM at the field scale. It computes the rate of biological decomposition of crop residue or organic amendments as they convert to SOM. It is a Microsoft Windows based program that was recently modified to include the effects of soil texture and drainage classes on decomposition rate. The program uses Revised Universal Soil Loss Equation (version 1) c-factor files for crop rotation, yield, tillage and weather data. Additional required data include the number and thickness of soil layers, starting organic matter content and bulk density of each layer, and nitrogen content of the organic residues. Residue nitrogen content can be estimated from tables provided in the program if actual analyses are not available. CQESTR provides tabular or graphic trends in residue and soil organic matter content for the duration of any rotation. The program was calibrated using information from 60-year old long-term wheat-fallow rotation experiments conducted near Pendleton, OR and validated with long-term organic matter databases from various parts of North America. However, recent modifications have not been compared with field data. Initial simulations predict that management practices that remove crop biomass or promote microbial decomposition, inversion tillage and fallow, consume existing SOM. Practices that increase contributions to biomass, limit inversion tillage and provide annual root and shoot biomass return to the soil promote carbon storage. Projected trends of SOM content at two sites for the GRACEnet (Greenhouse Gas Reduction through Agricultural Carbon Enhancement network) study are provided for illustration and discussion.