Simulating nitrate and pesticide concentrations in the subsurface drain water using the DRAINAGE model

Abstract

The DRAINAGE model (Kanwar et al., 1983) was modified by changing the soil layer thickness from 15 cm to 5 cm to simulate subsurface drain flows. Field data on subsurface drain flows for growing seasons of 1984 through 1991 were used for model calibration and validation from one of the water quality research sites in Iowa. The modified model was calibrated with subsurface drain flow data from 1986. The results of this study indicate that subsurface drain flows predicted by the modified DRAINAGE model were in close agreement with the observed values of subsurface drain flows, although peak subsurface drain flows were underpredicted. The overall results of this study indicate that reduced soil layer thickness significantly improved the model performance. Introduction Much of the midwestem United States is characterized by fertile, flat soils with adequate rainfall, but many of these soils need artificial subsurface drainage improvement for intensive agriculture. Understanding the impacts of agricultural water management techniques on the environment, especially those associated with the drainage of excess water from the soil profile, is important for modem agricultural production in the United States. Historically, subsurface drains were not installed as water quality management tools, but they do have a role