Prediction of NO3--N leaching in the unsaturated zone is difficult owing to the complex nature of processes dominating the fate of N in soils. Although many sophisticated numerical models have been developed for simulating nitrogen behavior in the soil-plant system, applying them in practice is often difficult, owing to the limited specific-site information. A lumped parameter model (LPM) for the assessment of nitrate leaching using limited data is presented. An LPM considers nitrogen transformation processes, climate data, and irrigation and fertilizer applications. The model was tested against detailed numerical models and against field data and provided realistic estimates of leachate at the bottom of the root zone. The model can be used for decision making regarding of nitrogen-N application and can provide an alternative way to estimate leachate loading to the groundwater. ¿ 1998 American Geophysical Union