Study of weed growth and its interaction with direct-seeded rice (DSR) under different herbicides and irrigation conditions

Rice cultivation continuously remains important for food and livelihood security. The forecasts of increasing water shortage under a changing climate and rising labour scarcities in agriculture have brought a paradigm swing in rice cultivation from the transplanting method (flooded) to direct-seeded rice (DSR). Despite all these returns, the potential yield losses through enormous weed threats under DSR remain a challenge and may reduce yield by up to 50 %. Several Southeast Asian nations have seen a transition in long-term DSR agriculture towards dominating grassy weeds, including Echinochloa crusgalli, Leptochloa chinensis and Ischaemum rugosum. DSR favours the proliferation of grasses and sedges over broadleaf weeds due to the absence of flooding, which is a natural weed suppressant in TPR. Early flooding in TPR can effectively suppress weed emergence, whereas DSR offers limited scope for early flooding since most rice cultivars are intolerant to anaerobic conditions during the germination process. However, anaerobic germination-tolerant rice varieties may enable early flooding and better weed control in DSR. Soil moisture, tillage techniques and application time all have a significant impact on their control efficacy. Crop phytotoxicity and decreased herbicide efficacy might result from improper soil moisture at the time of application. Herbicides may be washed away by excessive irrigation after application, while absorption may be hampered by inadequate moisture. Studies advise using herbicides soon after irrigation when the soil is sufficiently saturated. The efficacy of herbicides is also affected by variations in seasonal rainfall. For DSR systems to maintain productivity and reduce weed-related losses, integrated weed management, which includes prudent herbicide usage and water management, is essential.