Weed Community Structure and Dominance Indices in Irrigated Rice Under Alternate Wetting and Drying Water Management

Abstract

Weed flora composition and dominance patterns were evaluated in irrigated rice fields managed under alternate wetting and drying irrigation regimes to understand the ecological response of weed communities to changing water availability. Field experiments were conducted during the rice-growing season using standardized quadrat sampling to assess weed density, frequency, abundance, and species distribution at different crop growth stages. Phytosociological analyses revealed substantial variation in weed community structure between alternate wetting and drying conditions and continuously flooded fields. Broadleaf weeds, sedges, and grasses exhibited differential adaptation to fluctuating soil moisture levels, resulting in shifts in species composition and dominance throughout the season. Species diversity indices, including Shannon–Wiener diversity, Simpson dominance, and relative importance values, indicated greater weed diversity under alternate wetting and drying management compared with permanent flooding systems. Dominant weed species demonstrated high ecological plasticity and competitive ability under intermittent moisture stress conditions, contributing to increased interference with rice growth. Seasonal observations showed that periodic soil aeration promoted emergence of upland-adapted weed species while reducing the abundance of certain aquatic weeds commonly associated with flooded rice ecosystems. Weed biomass accumulation and dominance indices were significantly influenced by irrigation scheduling, crop canopy development, and nutrient availability. The altered hydrological environment created by alternate wetting and drying irrigation affected weed succession dynamics and competitive interactions within the rice agroecosystem. Understanding weed community responses to water-saving irrigation strategies is essential for designing effective and environmentally sustainable weed management programs.