Production potential of cover crops in the semi arid Southern Great Plains

Sustainable agriculture in the United States is increasingly integrating regenerative principles to address the challenges of soil degradation, declining organic matter, and climate variability. Cover crops have emerged as a potential strategy to address these challenges along with an optional economic source as forage. However, their performance in semi-arid regions such as the Southern Great Plains remains inconsistent due to limited moisture availability, and several adoption barriers. This thesis investigates the potential of integrating summer cover crops into dryland cropping systems and winter cover crops in cotton cropping systems in the Oklahoma Panhandle. The first objective of this research explores the role of cover crops in fallow periods within a dryland wheat–sorghum–fallow rotation. A two-year field study (2023–2024) evaluated Pearl Millet (Pennisetum glaucum) and Sorghum-Sudangrass (Sorghum × drummondii) for their forage yield, nutritive value and soil moisture consumption. Our results showed that longer growing periods significantly improved biomass yield and crude protein content, with Pearl Millet outperforming Sorghum-Sudangrass in both quality and yield during both years of study. Environmental conditions, harvest timing, and fertilization were critical factors influencing forage performance. The dedicated cover crops extracted similar amounts of soil moisture as by weeds in check plots, which was recharged by seasonal rainfalls following natural termination of covers. These findings suggest that cover crops can be used for fallow replacement, although long-term impact on grazing and moisture dynamics require further investigation. The second objective addressed the establishment of winter cover crops in irrigated cotton systems. The cotton harvest offers a narrow window for cover establishments in the region. The inter-seeding/broadcasting of covers in standing crops and the impact of harvest aids on covers has not been addressed yet. Therefore, a controlled-environment pot study tested impact of two cotton harvest aids (DFT-6 EC and Aim EC) on six winter cover crops. Green cover declined by at least 50% in all species within two weeks post-spray, with winter pea suffering complete loss. These findings suggest that inter-seeding cover crops in standing cotton is viable only if adequate time is provided (≥6 weeks) to achieve sufficient growth prior to defoliant application.