The USDA Root Zone Water Quality Model

Publication date: 06-02-2026
Extent: 54 pages

Contributions by: Huihui Zhang, Liwang Ma and Jon D. Hanson, USDA-ARS, USA; and Zhiming Qi, McGill University, Canada

Chapter synopsis:

The USDA Root Zone Water Quality Model (RZWQM), developed in the 1980s and released in 1992, simulates root zone processes based on earlier models like CREAMS, GLEAMS, and NTRM. It includes modules for water balance, soil carbon and nitrogen cycling, plant growth, energy balance, solute transport, phosphorus dynamics, and management practices. The original version featured a generic plant module (GPM) and was primarily used for maize, soybean, and wheat. In the early 2000s, RZWQM was combined with the DSSAT crop model to create RZWQM2 including 30 crop-specific modules. Later, the HERMES model was added with support for 15 crops. RZWQM2 features a Windows interface for data handling and parameter estimation. The model has over 450 publications and has been used for real-time irrigation scheduling of cotton and maize. Maintained by USDA-ARS scientists, RZWQM2 is available online and, with proper calibration, can simulate crop production and environmental quality under diverse conditions.

DOI: 10.19103/AS.2025.0155.25