Background of the MSEA-RZWQM modeling project

The Management Systems Evaluation Areas (MSEA) project was established in 1 990 as a part of the Midwest Water Quality Initiative to evaluate the effec t of agricultural management practices and systems on the quality of water resources, to increase understanding of processes affecting water contamina tion, and to develop cost-effective strategies to reduce water contaminatio n from pesticides and plant nutrients. The Midwest was chosen because it pr oduces so much of the country's corn (>80%) and soybean (approximate to 70% ) crops, and consumes >50% of the N fertilizer and almost 60% of the herbic ides applied. The MSEA project collected a large volume of data across a wi de region. Properly calibrated and validated, simulation models could use t his database to estimate water quality impacts over much longer periods tha n the expected life of the MSEA field program and to simulate responses for other combinations of soils, management systems, and weather conditions. T he Root Zone Water Quality Model (RZWQM) was chosen for model improvement, calibration, and validation, to be followed by multilocation simulation of several specific management systems used in Midwest corn and corn-soybean p roduction. Model improvement was an iterative process across multiple locat ions. The next seven papers in this issue provide an overview of RZWQM Vers ion 3.2, an explanation of the calibration-validation process, and document ation of that process and the modeling at MSEA locations in Iowa, Minnesota , Missouri, Nebraska, Ohio, and Colorado.