EFFECT OF WATER-TABLE MANAGEMENT-PRACTICES ON THE TRANSPORT OF NITRATE-N TO SHALLOW GROUNDWATER

Field experiments were conducted for three years (1989-91) at the rese arch farms of Iowa State University near Ames and Ankeny to evaluate w ater-table management (WTM) effects on groundwater quality. Water-tabl e depths of 0.3, 0.6, and 0.9 m were maintained in field lysimeters at the Ames site, and variable water-table depths were maintained in a s ubirrigation field at the Ankeny site. Water samples were collected fr om various soil depths to analyze NO3-N concentrations in groundwater. Concentration of NO3-N in groundwater changed with WTM practices. The lowest NO3-N concentrations were observed under the shallow water-tab le depths. NO3-N concentrations in groundwater generally decreased wit h increased depths and time during the growing season under all WTM pr actices. Crop yields were higher under water-table depths of 0.6 to 0. 9 m than under other water-table depths, and corn yields decreased und er shallow water-table depths of 0.2 to 0.3 m. Results of this study i ndicate that WTM practices can be used to substantially reduce the con centrations of NO3-N in groundwater, Results also strongly support the need for further research with WTM practices for water quality and cr op production.