Weed Species Composition and Abundance in Direct-Seeded vs. Transplanted Rice Under Varying Water Management Regimes

Abstract

Weed infestation patterns in rice-based cropping systems are strongly influenced by establishment methods and water management practices, affecting crop productivity and resource use efficiency. Comparative field studies were conducted to evaluate weed species composition, density, and dry biomass in direct-seeded rice (DSR) and transplanted rice (TPR) under different irrigation regimes including continuous flooding, intermittent irrigation, and aerobic conditions. Weed flora assessments revealed a higher diversity and abundance in DSR systems compared to TPR, with grasses such as Echinochloa crus-galli, sedges including Cyperus difformis, and broadleaf weeds dominating across treatments. Continuous flooding significantly reduced overall weed density, particularly in transplanted plots, whereas aerobic and intermittent water management promoted higher emergence and faster weed establishment in DSR systems. Quantitative analysis indicated that weed dry biomass was consistently higher under aerobic conditions, reflecting favorable germination environments for multiple weed species. Species richness and Shannon diversity index values were elevated in DSR plots, indicating greater ecological niche availability under non-flooded conditions. Interaction effects between establishment method and water regime demonstrated that transplanted rice under continuous flooding exhibited the lowest weed pressure, while direct-seeded aerobic rice recorded maximum infestation levels. These differences significantly influenced crop–weed competition dynamics and highlight the role of water as a key determinant in weed community structure. The findings emphasize the necessity of tailored integrated weed management strategies combining water management, competitive cultivars, and timely herbicide application to suppress weed pressure effectively. Overall, establishment method and irrigation regime jointly shape weed ecology in rice systems, directly impacting sustainable rice production under resource-constrained and climate-variable environments.