Modeling Nitrogen Movement Through Loess Soils

by Kenneth W. Rojas, USDA-ARS, Ft. Collins, United States,
Allen T. Hjelmfelt, Jr., USDA-ARS, Ft. Collins, United States,

Document Type: Proceeding Paper

Part of: Irrigation and Drainage


This study evaluates the ability of the Root Zone Water Quality Model (RZWQM) to track the movement and fate of nitrate (NO3--N) in deep loess soils. RZWQM is a physically-based, process-oriented model that includes the major physical, chemical, and biological processes that are of interest in agricultural systems. To evaluate the model, two field-sized watersheds managed by the ARS and located in western Iowa were used. These two fields were cropped to corn, using conventional contour tillage. On one of these fields, nitrogen fertilizer was applied at the normal recommended rate of 168 kg/ha for the years 1963-1973. On the other field, the application rate was tripled to 448 kg/ha for the years 1969-1973. This excess resulted in a bulge of nitrate moving downward. For this study we looked only at the model performance tested against this excessively fertilized field. The results show that the model is capable of accurately determining the movement, use, and production of nitrate against observed data recorded within the system described.

Subject Headings: Nitrogen | Loess | Model accuracy | Soil water movement | Biological processes | Chemical processes | Field tests | Water quality | Iowa | United States

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