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United States Department of Agriculture

Agricultural Research Service


item Hanson, Jonathan

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: September 1, 1997
Publication Date: N/A

Interpretive Summary: The Rooot Zone Water Quality model was developed to predict the relative response of various crops to changes in soil water and chemistry in conjunction with different management practices, including chemical applications. The crop growth and development component of the model is critically important so that hte relative responses of important crops to environmental variance and management manipulation can be determined. The theory and development of the model are presented. Subsequently, the model was used to simulate corn and soybean production for the Management Systems Evaluation Areas (MSEA) USDA research project. The model was successfully calibrated for corn and soybean at seven sites within the Midwester United States and Colorado. When correctly calibrated, errors were less then 10% of measured field values for aboveground biomass and yield. Validation results for corn and soybean were good so long as the water and nitrogen dynamics were simulated properly. In cases where large discrepancies occurred in predicting nitrogen or water content in the soil profile, particularly for the Missouri no-till management system, larger deviations occurred in the predicted biomass and yield for the crops tested. The user must make certain that errors in simulating water and nutrient dynamics are minimal if good predictions of yield are desired. The model also showed good response to nitrogen application. Results show that the effects on final crop yield are not linear. Therefore, RZWQM can be useful in determining optimal amounts of N to apply when crop yield, cost of application, and excess nitrogen leached through the root zone are simultaneously considered.

Technical Abstract: The Root Zone Water Quality Model (RZWQM) is a comprehensive simulation model designed to predict the hydrologic response, including potential for ground-water contamination, of alternative crop-management systems. The model is general enough to predict the relative response of various crops to changes in soil water and chemistry in conjunction with different management practices, including applications. Chemical applications are defined as any chemical added to the crop to increase growth rate or quality of the plant or to remove undesirable biological components from the system (such as insects or weeds). Management practices include other anthropogenic influences used to modify the environment or cropping sequence in order to improve the productivity of the desired crop, i.e. irrigation, time of seeding, cropping methodology, etc. The objective of this effort was to develop a generic crop-production model capable of predicting the relative responses of several important crops to environmental variance and management manipulation. Selected crops include but are not limited to, corn, soybean, dry beans, wheat, and various grasses. The discussion of the RZWQM plant comoponent includes a general overview of the model, a detailed discussion of the model structure, an examination of the primary model parameters, and examples to show how the model functions.

Last Modified: 5/27/2015
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