Degree Type

Thesis

Date of Award

2017

Degree Name

Master of Science

Department

Agricultural and Biosystems Engineering

Major

Agricultural and Biosystems Engineering

First Advisor

Matthew J. Helmers

Abstract

Artificial subsurface drainage, while necessary to maintain agricultural production in the soils and climate of the northern U.S. corn belt, can result in adverse environmental impacts. A major concern is the disproportionately large nitrate loads from agricultural lands with artificial drainage in the northern U.S. corn belt that contribute to the hypoxic zone in the Gulf of Mexico.

The first chapter in this thesis investigated the impacts of two conservation practices on soil temperature and moisture. The first conservation practice investigated is no-till compared to a fall chisel plow system in a north-central Iowa site. This study found that no-till significantly increased average daily soil moisture content prior to planting of a cash crop. No-till frequently had colder soil temperatures in the spring and summer compared to a chisel plow treatment. Corn residue had more of an impact on soil temperature and moisture than soybean residue. The second conservation practice investigated in the first chapter is a winter cereal rye cover crop at a north-central Iowa site and a central Iowa site. The central Iowa site had greater rye biomass which was associated with an increase in soil water even when rye was transpiring, while the north-central Iowa site had lesser rye biomass which was associated with a decrease in soil water whether rye was growing or had been terminated.

The second chapter in this thesis investigated the impact of no-till and a winter rye cover crop on seasonal and annual nitrate-N concentration and nitrate-N loading in leachate from artificial subsurface drainage. No-till and a rye cover crop with chisel plow significantly and consistently decreased nitrate-N loading and concentration in leachate on both the seasonal and annual scales compared to the chisel plow only treatment. Compared to no-till, a winter rye cover crop with no-till did not reduce nitrate-N loading or concentration in leachate. This is likely due to a combination of low nitrate-N leaching potential from no-till, and low rye biomass values throughout the entire study with no-till. Overall, both cover crops and no-till showed potential for improving nitrogen management with respect to water quality.

Future research should focus on increasing rye biomass in a northern climate, as this may alleviate soil water depletion concerns and increase the likelihood of rye biomass mitigating nitrate-N leaching off-site. Additionally, studies in long-term no-till situations, production scale drainage, and on different soil types should be considered for a better prediction of the broader scale impacts of no-till on nitrate-N leaching.

Copyright Owner

Emily Rose Waring

Language

en

File Format

application/pdf

File Size

266 pages

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