Impacts of Cover Crops on Nutrient Loading in Headwater Streams Draining Southern Illinois Row Crop Fields: A Paired Watershed Approach

Author

Steven Micheal Bachleda, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2023

Degree Name

Master of Science

Department

Forestry

First Advisor

Schoonover, Jon

Second Advisor

Williard, Karl

Abstract

AbstractAccording to the EPA (2008), nutrient loading is the process of dissolved or particulate nutrients entering a water body via surface runoff, subsurface, or groundwater flow. Excess nutrient loading, caused by agricultural runoff from fertilizer inputs, contributes to pollution in waterways which can cause health and economic concerns (Bosch, NS, et al., 2019). Best management practices (BMPs) in agriculture can reduce a portion of the nutrient runoff from the fields. This study investigates the impacts that implementing cover crops (CCs) of cereal rye (Secale cereale) and hairy vetch (Vicia villosa) as BMPs on nutrient runoff into streams and consequently the nutrient loading in those streams as well as how they impact the soil water nutrient concentrations. This was done in two ways, a paired watershed approach and a plot scale approach. The paired watershed approach investigates the large-scale impacts on stream nutrients that implementation of CCs have on a watershed scale. Paired watershed studies are few in numbers as the parameters for this type of study are difficult to achieve. The findings show that CCs can increase concentrations of nutrients in the surrounding streams, however they reduce discharge in streams by 16% to 70% depending on the time of year and what CC is planted. This reduction of discharge in streams caused by higher evapotranspiration rates during the spring reduced loading of sediment and nutrients such as total suspended solids (TSS) between 69% to 77%, dissolved reactive phosphorus (DRP) by 22.2% to 48%, nitrate by 52% to 84.5%, and ammonium by 51% to 57.3% depending on the time of year and what CC was planted. The plot scale approach looked in depth at how CCs impact soil water nutrient concentration utilizing tension lysimeters, biomass sampling, nitrogen uptake (N-uptake) by CCs, and soil sampling for soil phosphorus stratification within the treated region of the watershed. This was examined both seasonally and topographically to better estimate where targeted usage of CCs would create the best outcome for nutrient reduction. CCs were found to have reduce soil water nutrient concentrations of all examined nutrients over the entire study. During all the CC seasons combined of cereal rye and hairy vetch, only DRP and nitrate were reduced whereas during just the cereal rye seasons DRP, nitrate, and TN were reduced. The HV seasons only significantly reduced DRP during its growing period. The hills in the fields were split into three categories of topographic elevations, shoulder (top of the hill), backslope (middle of the hill), and footslope (the bottom of the hill). Topography interaction within the CC watershed showed a decrease in nitrite, nitrate, and TN between the footslope position and the backslope position. Between the footslope position and shoulder, nitrate and TN were significantly higher in the shoulder position. Between the backslope position and the shoulder position in the CC watershed only DRP was significantly different with DRP being higher in the shoulder. Biomass on the fields during the fallow season were significantly deferent between the CC and No-CC watershed depending on CC species, the time of planting, time of termination, and weather. The earlier the CCs were planted the more successful they were at producing biomass and increasing N-uptake. Three out of the six sampling years CCs were found to have significantly higher biomass and N-uptake than in the No-CC watershed. Topography also played a major role in the success of biomass production of CCs. Three of the six years showed highly significant changes of biomass in a gradient from low to high correlated with elevation. This is due to large amounts of precipitation causing pooling of water in the lower parts of the watershed which reduced biomass growth. Soil phosphorus stratification was shown to be present in all plots in both watersheds. The CC watershed had more consistent amounts of soil phosphorus throughout the different topographic positions than the No-CC watershed. However, there was a downward trend implying that with further research, a definitive answer may be found that if over time, CCs could potentially reduce stratification. This study showed that CCs have a positive impact on reducing nutrient loading into streams and soil water but highlights the need for targeted planting of the species and sufficient planning to maximize success in mitigating nutrient export from agricultural fields.