|Douglas Jr, Clyde|
Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2001
Publication Date: N/A
Interpretive Summary: The continued increase of carbon dioxide concentration of the earth's atmosphere is suspected of contributing to troublesome environmental and weather events associated with global warming. One possible method for reducing the net release of carbon dioxide is to recapture the carbon dioxide with crop plants (photosynthesis) and retain as much as possible of the unused crop residue in agricultural soils as organic matter. If this practice is to be utilized, a predictive tool for relating cropping practices to their impact on soil organic matter, and the subsequent release or storage of carbon, will be required. The PC based model CQESTR, pronounced "sequester", provides this tool. It utilizes readily available input data. Its predictions are applicable to individual fields. Validation tests show it to predict OM content within 0.5% OM, 95% of the time. The model is being tested for possible utilization nationally in the USA and can be evaluated for international application.
Technical Abstract: Carbon sequestration in agricultural soils is controlled primarily by the balance of organic residues applied to the soil and the microbial oxidation of both those residues and the native organic matter (OM) as moderated by agricultural management and tillage practices. The PC based model CQESTR, pronounced "sequester", predicts weight loss to decomposition of crop residues, organic amendments and soil OM based on cropping practices. Emphasis is placed on the first four years of decomposition of residues. Input for CQESTR includes existing RUSLE (Revised Universal Soil Loss Equation) c-factor files, with their associated croplist.dat and oplist.dat files. These data are supplemented with residue nitrogen content and soil organic matter content, bulk density, and layer thickness. CQESTR was calibrated with soil carbon data from residue management experiments with 70 years of recorded history at the Research Center at Pendleton OR. The calibrated model provides estimates with a 95% confidence interval or 0.33% OM. The comparison of model predictions with observations of OM from 11 independent sites where soil OM observations and associated cropping and management histories were available, resulted in a matching of observed with calculated OM with a 95% confidence interval of 0.55% OM. A 12th site, where a history of severe erosion occurred on the field plots, provided a poor match with computed OM.