Degree Type


Date of Award


Degree Name

Master of Science


Agricultural and Biosystems Engineering


Agricultural and Biosystems Engineering

First Advisor

Matthew J. Helmers


The upper Midwest region has been dramatically altered since it was first settled in the 1800’s. What was once dominated by perennial vegetation and wetland is now dominated by annual grain cropping systems, many artificially drained. These changes have made the landscape susceptible to nutrient loss that contributes to water quality degradation, including hypoxia in the Northern Gulf of Mexico. Nutrient reduction strategies, such as alternative drainage systems and a Cereal rye (Secale cereal L.) cover crop, have been cited for their success in reducing nutrient losses from row-crop agricultural systems.

The first study within this thesis examines subsurface drainage systems with an agricultural simulation model, RZWQM. We tested RZWQM using nine years (2007-2015) of field data from Southeast Iowa for controlled drainage (CD), shallow drainage (SD), conventional drainage (DD) and undrained (ND) systems, and simulated the long-term (1971-2015) impacts. RZWQM accurately simulated N loss in subsurface drainage, showing that CD and SD substantially reduced N loss. Long-term, RZWQM predicted a 26% N-loss reduction in CD and 40% in SD. During the spring (April-June), CD was found to be less effective (11% reduction) than SD (35% reduction). Improvement of CD systems within the spring to reduce N loss across the upper Midwest landscape may be required.

The second study investigates how delaying Cereal rye termination before soybeans impacted moisture and temperature within the soil profile from 2015 to 2016. In the early termination treatment (EC), rye was killed two weeks before corn planting and in the late termination treatment (LC), rye was killed two weeks before planting corn and 6-17 days before planting soybeans. Delaying termination prior to soybeans increased rye biomass accumulation, on average by 3.5 times. Despite rye water use, rye treatments stored the same or more moisture from 0-50 cm than NC from mid-April to mid-October, indicating a mulching effect by the residue. Cover crop treatments were cooler and wetter during corn planting, which may be detrimental to germination. Delaying rye termination prior to soybeans reduced moisture content in the early spring, however this was quickly replenished and promoted greater water content during soybean flowering and grain fill, which could positively impact yield in a dry year.


Copyright Owner

Kristina Jo Craft



File Format


File Size

130 pages