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United States Department of Agriculture

Agricultural Research Service

Research Project: SOIL CONSERVATION SYSTEMS FOR SUSTAINABILITY OF PACIFIC NORTHWEST AGRICULTURE

Location: Soil and Water Conservation Research

Title: Simulating Soil Organic Matter with CQESTR (v.2.0): Model Description and Validation against Long-term Experiments across North America

Authors
item Liang, Yi - FORMER ARS EMPLOYEE
item Gollany, Hero
item Rickman, Ron - RETIRED USDA-ARS
item Albrecht, Stephan
item Follett, Ronald
item Wilhelm, Wallace
item Novak, Jeffrey
item Douglas, Clyde - RETIRED USDA-ARS

Submitted to: Ecological Modelling
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 2008
Publication Date: February 24, 2009
Citation: Liang, Y., Gollany, H.T., Rickman, R.W., Albrecht, S.L., Follett, R.F., Wilhelm, W.W., Novak, J.M., Douglas, C.L. 2009. Simulating Soil Organic Matter with CQESTR (v.2.0): Model Description and Validation against Long-term Experiments across North America. Ecological Modelling. 220(4): 568-581.

Interpretive Summary: Soil organic matter (SOM) has important chemical (supplies plant nutrient, buffers and filters harmful chemical compounds), biological (supports the growth of microorganisms), and physical (improves soil structure and soil tilth, stores and transmits air and water, and reduces surface crusting, water runoff, and soil erosion) functions. Developing tools that predict change in SOM with change in management to assist land managers in creating sustainable crop residue and SOM management practices becomes increasingly important as crop residues are targeted for additional uses (i.e., cellulosic ethanol feedstock). CQESTR, pronounced sequester, is a process-based carbon balance model. The name CQESTR is a phonetic condensation of the words carbon sequestration, which means carbon storage. It computes the rate of biological decomposition of crop residue or organic amendments as they convert to SOM. This model was developed for national use in U.S and calibrated initially in the Pacific Northwest. Our objectives were: (i) to revise the model, making it more applicable for wider geographic areas including potential international application, by incorporating soil texture and drainage effects, and (ii) to recalibrate and validate it for an extended range of soil properties and climate conditions. The current version of CQESTR (v. 2.0) is presented with the algorithms necessary to simulate SOM at field scale. Input data for SOM calculation include crop rotation, aboveground and belowground biomass additions, tillage, weather, and the nitrogen content of crop residues and any organic amendments. The model was validated with long-term data from across North America. Regression analysis of 306 pairs of predicted and measured SOM data under diverse climate, soil texture and drainage classes, and agronomic practices at 13 agricultural sites having a range of SOM (0.73-5.79%), resulted in a very significant (P < 0.0001) linear relationship (r^2 = 95%) with a 95% confidence interval of 0.43%. Using the same data the version 1.0 of CQESTR had an r^2 of 0.71 with a 95% confidence interval of 0.55%. Given the high correlation of simulated and observed SOM changes, CQESTR can be used to consider a wide range of scenarios before making recommendations or implementing proposed changes. The development of soil management practices that maintain adequate SOM for nutrient cycling, soil structure stability, and sufficient biomass to prevent erosion is essential for decisions on land use when planning crop rotation, tillage, and other management options in a time when agriculture’s role is expanding beyond the production of food, feed, and fiber, to one where the need to produce biofuel feedstock may exceed the combined need for production to address traditional demands.

Technical Abstract: Soil carbon (C) models are important tools for examining complex interactions between climate, crop and soil management practices, and to evaluate the long-term effects of management practices on C-storage potential in soils. CQESTR is a process-based carbon balance model that relates crop residue additions and crop and soil management to soil organic matter (SOM) accretion or loss. This model was developed for national use in U.S and calibrated initially in the Pacific Northwest. Our objectives were: (i) to revise the model, making it more applicable for wider geographic areas including potential international application, by incorporating soil texture and drainage effects, and (ii) to recalibrate and validate it for an extended range of soil properties and climate conditions. The current version of CQESTR (v. 2.0) is presented with the algorithms necessary to simulate SOM at field scale. Input data for SOM calculation include crop rotation, aboveground and belowground biomass additions, tillage, weather, and the nitrogen content of crop residues and any organic amendments. The model was validated with long-term data from across North America. Regression analysis of 306 pairs of predicted and measured SOM data under diverse climate, soil texture and drainage classes, and agronomic practices at 13 agricultural sites having a range of SOM (7.3-57.9 g SOM/kg), resulted in a linear relationship with an r^2 of 0.95 (P < 0.0001) and a 95% confidence interval of 4.3 g SOM/kg. Using the same data the version 1.0 of CQESTR had an r^2 of 0.71 with a 95% confidence interval of 5.5 g SOM/kg. The model can be used as a tool to predict and evaluate SOM changes from various management practices and offers the potential to estimate C accretion required for C credits. [GRACEnet and REAP publication].

Last Modified: 8/27/2014