Doctoral Dissertations

Orcid ID

https://orcid.org/0000-0003-2301-730X

Date of Award

5-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Natural Resources

Major Professor

Patrick Keyser

Committee Members

Virginia Sykes, Gary Bates, Robert Florence

Abstract

Utilization of various cover crops during native warm-season grass (NWSG) establishment presents an opportunity to mitigate the lost forage production that has come to be a hallmark of NWSG establishment. Successful application of a productive cover crop could help overcome a major barrier to NWSG adoption. Another potential benefit to the use of cover crops is their ability to suppress weeds. Studies addressing the use of various cover crops in the Southeastern US have thus far largely focused on the use of cereal crops as companion crops during NWSG establishment which are then harvested for hay upon reaching maturity. The trials presented in the following work were developed to evaluate the use of nurse crops during NWSG establishment to offset loss of forage production during the seedling year. The first study evaluated the use of two nurse crops, a warm season diversity blend (DB) (Ray’s Crazy Mix, Southeast AGRISEEDS, Rome, GA), and browntop millet (BTM) (Urochloa ramose (L.) Nguyen), to reduce weed pressure and provide a source of livestock forage during the seedling year as well as the effects of grazing these nurse crops on the first-year establishment of the co-planted NWSGs (Chapter 2). The second study design looked to elucidate the role of thatch groundcover depth and composition on suppressing weeds and NWSG seedling recruitment (Chapter 3). The final trial utilized the controlled environment of a greenhouse to evaluate the sensitivity of NWSG germination and early seedling development to soil phosphorus (P) and pH levels (Chapter 4). In the first trial, both nurse crops reduced weed pressure while also reducing NWSG recruitment. Grazing did not affect NWSG recruitment but was successful at reducing weed pressure and allowing more light to penetrate the canopy. In the second trial, thatch depth played a driving role in NWSG recruitment while thatch type had no effect. Imazapic synergized with grazing to reduce weed canopy cover (WR) compared to the CTRL and non-grazed treatments. In the greenhouse trial soil increasing P generally benefited BBS seedling growth metrics, while pH as low as 4.5 had no effect on seedling germination, tillering, or root growth, but did interact with P to increase plant height. Mid-season clipping negatively affected end of season above ground plant height, overall plant mass, and tiller number, but did not affect root length, mass, or root to shoot ratio.

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