Date of Award
5-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Plant and Environmental Science
Committee Chair/Advisor
Dr. Matthew A. Cutulle
Committee Member
Dr. Brian K. Ward
Committee Member
Dr. Michael W. Marshall
Committee Member
Dr. Raghupathy Karthikeyan
Committee Member
Dr. Sarah A. White
Abstract
Rice (Oryza sativa L.) production in coastal agroecosystems is increasingly threatened by rising soil salinity and persistent weed pressure, particularly under organic management systems where chemical control options are limited. Saltwater intrusion driven by tidal flooding and sea-level rise disrupts soil properties, plant physiological processes, and crop productivity, while competition from weed species further intensifies stress and yield loss. Although both stressors individually constrain rice production, their combined effects remain insufficiently understood, especially for heirloom cultivars, such as Carolina Gold, grown in coastal Carolinas. This research evaluated rice responses to combined salinity stress and weed competition to identify cultivars with improved tolerance and competitive ability for saline coastal environments.
The research was conducted from 2022 to 2025 at the Clemson University Coastal Research and Education Center located in Charleston, South Carolina. In the first study, four rice cultivars (Carolina Gold, Santee Gold, Doble Carolina, and M202) were evaluated under controlled greenhouse conditions across five seawater salinity levels (0, 0.2, 0.4, 0.8, and 1.6 dS m⁻¹) under weed-free and weed-competition conditions. Increasing salinity elevated soil electrical conductivity and sodium accumulation while reducing calcium and phosphorus availability, resulting in reduced growth, physiological performance, and yield. Significant genotypic variation was observed, with M202 showing greater tolerance and Carolina Gold showing high sensitivity. Weed competition further reduced rice biomass and grain yield, particularly under saline conditions, while weed responses varied by species.
The second greenhouse study examined species-level crop–weed interactions under salinity using rice, barnyardgrass (Echinochloa crus-galli), and hemp sesbania (Sesbania herbacea). Increasing salinity significantly reduced rice chlorophyll content, plant height, and grain yield, with near-complete crop failure observed under combined high salinity and weed competition. In contrast, hemp sesbania maintained high emergence and growth across salinity levels, demonstrating greater tolerance and competitive dominance, while barnyardgrass exhibited intermediate responses. These differential species responses altered competitive dynamics under saline conditions.
The third field study evaluated six rice genotypes (Carolina Gold, Santee Gold, Doble Carolina, M202, Jupiter, and JN100) under field conditions across a wide salinity gradient (0, 1–6.4 dS m⁻¹) with natural weed pressure. Increasing salinity reduced weed biomass and crop growth, while weed competition decreased plant height, tiller density, panicle number, and biomass across salinity levels. Genotypic differences were pronounced, with M202 exhibiting the highest salinity tolerance (EC₅₀ > 6.4 dS m⁻¹) and Carolina Gold the greatest sensitivity (EC₅₀ < 1 dS m⁻¹). Tolerant genotypes maintained lower Na⁺/K⁺ ratios, higher photosynthetic activity, and reduced sterility under saline conditions.
Overall, this research demonstrates that combined salinity and weed competition reduces rice growth and yield more severely than either stress alone and alters crop–weed competitive dynamics through species-specific tolerance. The findings identify cultivars with improved salt tolerance, clarify how salinity modifies weed competition, and provide a foundation for developing integrated and sustainable rice production strategies in salt-affected coastal agroecosystems. These results contribute to improving the long-term viability of rice production while preserving heirloom rice systems in coastal environments.
Recommended Citation
Singh, Gursewak, "Exploring Salt Tolerance and Crop-Weed Interactions to Improve Organic Rice Systems in Coastal South Carolina" (2026). All Dissertations. 4280.
https://open.clemson.edu/all_dissertations/4280
Author ORCID Identifier
https://orcid.org/0000-0002-1302-578X