Understanding the Role of Cattle Grazing and Poultry Litter Application on Weed Proliferation in Agricultural Fields

Abstract

This thesis investigates the complex interactions between cattle grazing and poultry litter (PL) application on weed seed dispersal and proliferation in agricultural systems in the southern USA. The first study focuses on the germination and survival of five dominant weed species—Palmer amaranth (Amaranthus palmeri), yellow foxtail (Setaria pumila), johnsongrass (Sorghum halpense), field bindweed (Convolvulus arvensis), and pitted morningglory (Ipomoea lacunosa)—following incubation in bovine digestive fluid for eight different time periods (0, 4, 8, 12, 24, 48, 72, and 96 hours). The results reveal significant variation in seed germination among the species, with I. lacunosa reaching zero germination after 24 hours of incubation, whereas A. palmeri and S. halpense retained up to 3% germination even after 96 hours. The small seed size and hard seed coat of A. palmeri and S. halpense likely contributed to their high resistance to rumen fluid incubation, while the seed coat of I. lacunosa became easily permeable and ruptured. These findings suggest that cattle grazing can selectively affect weed seed distribution and invasiveness in grazed grasslands and rangelands, emphasizing the need for customized grazing practices to manage weed spread effectively. The second study examines the effects of PL from varying cleanout frequencies (6 months, 2 years, and >2 years) on weed emergence, growth, and corn (Zea mays) yield across field and controlled environments in Alabama. Field experiments at two locations demonstrate that PL application, with and without supplemental nitrogen, significantly increases weed density and biomass compared to full fertilizer and control treatments. Greenhouse trials support these findings, showing higher weed emergence and biomass in PL-treated plots. Palmer amaranth exhibited the highest responsiveness to PL, raising concerns about herbicide resistance management. Laboratory experiments assessed the impact of PL-soil ratios and leachate concentrations on seed germination, viability, and seedling growth. Results indicate that increasing PL ratios and leachate concentrations negatively affect A. palmeri germination and growth, while corn demonstrates greater resilience. Corn grain yield was significantly reduced in PL-treated plots with high weed densities, highlighting the competitive impact of weeds on crop production. Together, these studies provide valuable insights into the role of grazing and PL application in weed dispersal and management. The findings offer opportunities for developing integrated strategies, including customized feeding and grazing practices combined with timely removal of weeds at the pre-flowering stage, to enhance sustainable agricultural practices and effective weed control in the southern USA.