AbstractsBiology & Animal Science

Winter cover cropping has been identified as a conservation practice with the potential to decrease nutrient transport from agricultural fields, which consequently reduces nutrient loading to water bodies, eutrophication, hypoxia, and degradation of local ecosystems. This study utilized laboratory-scale soil columns and the one-dimensional water and solute transport model HYDRUS-1D to quantify and understand the potential decrease in nitrogen and phosphorus loss through tile drainage due to cover crops, as well as compare the amount of nitrogen and phosphorus available in the soil at cash crop planting, with and without a cover crop. Information from a method development period and literature review was used to design, construct, and execute an outdoor/indoor soil column experiment, which allows for both realistic weather conditions and an increased amount of experimental control. A 50/50 mixture of oats (Avena sativa) and hairy vetch (Vicia villosa) was grown in Flanagan silt loam soil columns August 2014 – January 2015 in Champaign, IL. In August, 201.8 kg ha-1 NO3-N and 50.4 kg ha-1 PO4-P were applied to a growing cover crop. Deionized water was applied at a rate of 4 L every two weeks in addition to natural precipitation. A well-established stand of oats/hairy vetch cover crop had 92% less nitrate leaching (total mass) over the growing period than bare soil. Additionally, a 65% increase in cover crop growth was shown to significantly decrease nitrate leaching compared to a thinner stand of cover crops within 95% confidence limits. Both drainage volumes and nitrate concentrations were reduced as a result of cover cropping. However, average nitrate concentrations from both bare and cover cropped soil columns were above 10 mg L-1, which is the acceptable limit for drinking water. This experiment simulates a “worst-case scenario” for nitrate leaching by combining fall fertilizer application with soil directly above a tile, but a “best-case scenario” with a profile initially free of macropores. Orthophosphate leaching was 2 – 3 orders of magnitude less than nitrate leaching (0.7 mg of orthophosphate and 87 mg of nitrate lost over growing season from densely cover cropped columns), but also decreased with cover crop use by 46%. The HYDRUS-1D model was successfully calibrated and validated for water flow from cover cropped and bare soil columns. However, the model under-predicted the effects of cover cropping on water and nitrate leaching. Future experiments conducted to provide model data for cover cropping should include measurements of root growth, leaf area index (LAI), soil pH, and estimations for crop nutrient uptake potential. Limitations of studies with repacked soil column were encountered and are addressed in detail. Recommendations for future soil column studies include increasing the time period allowed for natural settling of the soil column and introducing earthworms, quantifying the effects of soil temperature on nitrification and denitrification under cover cropping, and measuring… Advisors/Committee Members: Kalita, Prasanta K. (advisor).