Date of Award
Master of Science (MS)
Department of Geography-Geology: Hydrogeology
Catherine M. O'Reilly
Nutrient pollution originating from agricultural regions in the Midwest is a serious issue, leading to pollution of drinking water sources as well as large hypoxic zones in the Gulf of Mexico. The source of much of this contamination has been shown to be runoff from agricultural fields in the Upper Mississippi River Basin. One method that has been shown to reduce this pollution from the Upper Mississippi River Basin is the planting of winter cover crops. Winter cover crops such as rye and tillage radish have been shown to significantly reduce nitrate exported from agricultural fields, even in tile-drained watersheds that are resistant to other nitrate management methods such as riparian zones. However, most studies take place in small agricultural study fields, where planting and fertilization is tightly controlled. There is also a lack of studies looking at the effectiveness of cover cropping in reducing phosphorus export.
In this study, we looked at the effectiveness of winter cover crops in reducing nitrate and total phosphorus (TP) loading from tile- drained agricultural watersheds in Central Illinois. We compared nitrate loading from two agricultural watersheds that were 445 ha and 312 ha, one of which was 54% planted with cover crops in fall 2015 and fall 2016 while the other was left fallow. We used discharge probes and automatic sampling systems to capture high temporal resolution discharge and concentration data from tile drains draining each watershed, and using these measurements we compared nitrate and TP loading.
We found no noticeable pattern of nitrate or TP reduction in spring 2016, despite that period having the greatest total cover crop biomass. However, in the fall 2016 cover cropping period, there was a pattern of reduced nitrate loading at our treatment site relative to the loading at our reference site. This appears to be due to a statistically significant (p=5.045x10-9)reduction in discharge at the treatment site relative to the reference site during the fall 2016 cover cropping period. Nitrate loading reduction was particularly strong during periods of storm flow. The effects of cover cropping in fall 2016 were more mixed when it came to TP loading. There was a lesser percentage of TP that occurred during storm events at our treatment site during this period, but there was not a significant change (p=.0522) in TP loading relative to the reference site when incorporating baseflow. Further data is needed to define the TP loading patterns, and to more solidly establish the pattern of nitrate loading reduction.
Bruening, Benjamin Gerald, "Nutrient Loading Reduction in a Tile Drained Agricultural Watershed through Watershed-Scale Cover Cropping: a High Resolution Analysis" (2017). Theses and Dissertations. 747.