Effects of drainage water management in Southeast Iowa

Schott, Linda
Major Professor
Matthew J. Helmers
Committee Member
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Agricultural and Biosystems Engineering

Subsurface drainage, while necessary for maximizing row crop production in Iowa, short-circuits nitrate-N downstream. Drainage water management practices, such as controlled drainage and shallow drainage, have been shown to reduce NO3-N loss by reducing the volume of water leaving the field.

The first investigation in this thesis focuses on how drainage water management effects crop yield, drainage volumes, NO3-N loss, depth to water table, and volumetric water content using data eight years of data collected from 2007 to 2014 at a drainage research site in Southeast Iowa from four treatments: controlled drainage, shallow drainage, conventional drainage, and no drainage. Controlled and shallow drainage reduced NO3-N loads by 49% and 42%, respectively. There were yield reductions from the shallow and controlled drainage treatments, as well as no drainage, especially in wet years.

The second investigation concentrates on if drainage water management practices effected the planting dates of corn from 2012 to 2015 at the same research site. None of the four treatments affected volumetric water content near the surface where corn would be planted. Soil temperature at 10 cm was significantly greater in the undrained and shallow drainage treatments, but the reason is unknown. There were differences in depth to water table between treatments, which may impact the date of planting if the water table is near the surface.

The third study investigates how shallow and controlled drainage practices affected peak drainage and water table recession time compared to the conventional treatment for four small drainage events. There was no difference between treatments in the time to peak discharge, but shallow drainage increased peak discharge in two events wile controlled increased peak discharge during one event. There was no difference between treatments in time of water table recession,

Due to growing concerns over the hypoxia zone in the Gulf of Mexico, further research should be conducted for both drainage water management practices at other sites in Iowa and across the Midwest as a practice to reduce nutrient losses. This research should focus on how these practices can either maintain or increase crop yields to make these practices more affordable to producers.