Weed biology and crop-weed competition dynamics in direct- seeded rice ecosystems

The field experiment was conducted to assess the effects of weed competition on the growth and yield of direct-seeded rice (DSR) under puddled and unpuddled conditions at Tamil Nadu Rice Research Institute, Aduthurai, Thanjavur, during the Kharif seasons of 2019 and 2020. The experimental site, characterized by a sub-tropical climate and alluvial clay soil, demonstrated significant differences in weed emergence, with earlier sprouting observed in unpuddled conditions. Weed biology, particularly the germination patterns and growth rates of various weed species, was crucial in shaping weed competition dynamics. In unpuddled conditions, certain weeds, especially annual grasses, exhibited rapid seedling establishment, benefiting from the more open, less waterlogged soil conditions. Weed density assessments indicated higher competition levels in weedy plots, particularly 30 days after sowing, with grasses dominating the weed population. This was due to the higher viability and faster germination rates of these species under unpuddled conditions. Weed biology also revealed that weed species with deep root systems were better able to access nutrients and water deeper in the soil, which further intensified competition with the rice crop, particularly in unpuddled plots. In contrast, puddled conditions inhibited the growth of certain weed species by restricting oxygen access to their roots and promoting anaerobic soil conditions, which helped reduce the weed biomass and competition. Plant growth attributes, including height and tiller counts, were significantly greater in puddled DSR plots, resulting in higher yields than unpuddled plots. Notably, yield losses due to weed competition were most pronounced between 30 and 45 days after sowing, a critical growth phase when rice plants are most vulnerable to weed pressure. This period coincided with peak weed germination and establishment, which led to severe competition for light, nutrients and water. These results underscore the importance of understanding weed biology in the context of weed management strategies. Effective control measures, tailored to the biology of the dominant weed species in each system, are essential to maximizing DSR productivity. Furthermore, the advantages of puddled cultivation, which limit weed growth and improve rice yield, highlight its importance as a key practice in sustainable rice farming.