Date of Award
Master of Science
Environmental and Soil Sciences
Jaehoon Lee, Forbes Walker, Michael Essington
Cover crops (CC) offer a suite of agronomic services to soils. Cover crops have shown to control soil erosion and nutrient loss, increase soil organic matter, suppress weeds, as well as improve soil health. However, CC can also influence soil processes pertaining to nitrogen (N) availability. There is limited knowledge about the effects multi-species CC have on soil N dynamics and their N release throughout the row-crop growing season in the humid Southeastern US. This study leverages a field experiment initiated in 2013 at the University of Tennessee’s Research and Education Center in Milan, TN. The experimental design includes single-, double-, and multi-species CC treatments along with a control (no CC). This study aims to determine the seasonal changes in soil N pools across single-, double-, and multi-species CC compared to a CC-free control at different soil depths. A subsequent study was done to determine the in-situ rates of CC residue decomposition and N release in response to species types and degree of soil disturbance. The sub-focus of this study was to calculate a N credit to CC, to prospectively mitigate the rates of synthetic N inputs. Cover crops had no effect on plant available N within each sampling period, however there was a significantly higher increase of potential N loss out of the soil system within a month of CC termination. Cereal rye (Secale cereale) and CR with hairy vetch (Vicia villosa) showed a higher potential to mineralize organic-N throughout the growing season in comparison to the control. Overall, soil N pools were concentrated in the top soil depth (0-5 cm) and decreased with depth.Cereal rye and the multi-species mixture had the lowest amount of N remaining (33%) after the first 4 weeks after termination for surface placed CC residues. Tilled residues significantly released N faster in comparison to surface placed, where the N remaining in the residues ranged between 8 to 14% in the first 4 weeks. This study provides insight into how unique cover cropping strategies can be used to improve water and environmental health and potentially improve profitability to Southeastern US agro-ecosystems.
Sabbagh, Manuel, "Effect of Unique Cover Cropping Strategies on Soil Nitrogen Dynamics and Their Rates of Nitrogen Release. " Master's Thesis, University of Tennessee, 2019.