Differential response of seedling emergence from common weeds in paddy field to water depth variations

Weeds compete with rice plant for resources such as water, nutrients, light, and weed competition has become one of the key factors in reducing rice yields. The ecological control measures of weed management in paddy field have become the focus of current research. The seedling stage of plants is more sensitive to environmental changes, which is the key stage of weed control. However, studies on the effects of different water depths and intermittent flooding and drying treatments on weed seedling emergence, particularly in important rice-growing areas such as the Sanjiang Plain in China, remain relatively scarce. This study investigated the influence of different water depth gradients (0, 3, 6, 9, 12 cm) and alternating flooding-drying treatments on the emergence of four common paddy field weed species: Echinochloa crus-galli, E. crus-galli var. mitis, Bidens pilosa, and Alisma plantago-aquatica. The results demonstrate a significant interspecific divergence in seed emergence responses to hydrological regimes. Compared to control conditions, 12 cm water depth induces emergence reductions by 27.6%, 36.4% and 44.8% in Echinochloa crus-galli, E. crus-galli var. mitis, and Bidens pilosa, respectively. In contrast, A. plantago-aquatica maintains over 80% emergence under deepwater conditions, demonstrating superior aquatic adaptation. Notably, E. crus-galli shows no significant difference in emergence between continuous flooding and alternating flooding-draining treatments, whereas emergence rate in A. plantago-aquatica declines sharply by 47.9% - 84.5%. These results indicate that short-term water withdrawal can also inhibit the emergence of weed seeds to a certain extent. This study provides scientific basis for the selection of ecological control strategies for different type of weeds in rice fields.