Asiatic dayflower (Commelina communis L.) has recently emerged as a problematic species in dry direct-seeded rice (Oryza sativa L.) (DDSR) systems in China. Understanding its germination and emergence ecology is essential for developing effective integrated weed management strategies. However, information on the effect of diverse environmental factors on its germination and emergence ecology remains limited. This study evaluated the germination ecology of C. communis in response to temperature, light, osmotic stress, salinity, radiant heat exposure, wheat residue cover, and seed burial depth. Seeds failed to germinate at 20/10 C, whereas germination was initiated at 25/15 C (62%) and was highest at 35/25 C and 40/30 C (96% to 98%), regardless of light conditions. A three-parameter sigmoid model predicted 50% inhibition at −0.23 MPa osmotic potential and complete inhibition at −0.8 MPa. At increasing sodium chloride (NaCl) concentrations, 50% inhibition occurred at 191 mM NaCl, with complete inhibition at 350 mM NaCl, suggesting moderate salinity tolerance. Exposure to radiant heat (≥160 C for 5 min) completely inhibited germination, suggesting that residue burning may be an effective control measure. Seedling emergence was greatest (91%) on the soil surface but declined sharply with increasing burial depth, with no emergence observed beyond 13 cm. Increasing wheat residue reduced seedling emergence, with significant reductions observed at higher residue rates (notably 6 and 10 Mg ha⁻1). These findings offer crucial insights into C. communis germination ecology and have practical implications for its integrated management in DDSR systems. They also provide an ecological framework for optimizing the timing of weed control, seedbank management, and tillage practices in Chinese DDSR systems.

Alkali barnyardgrass [Echinochloa crus-galli var. zelayensis (Kunth) Hitchc] and junglerice [Echinochloa colona (L.) Link] are problematic annual weeds in direct-seeded rice (Oryza sativa L.) fields in China. The emergence ecology of the two weed species may differ in response to environmental factors. Laboratory and screenhouse experiments were conducted to evaluate the effects of light, burial depth, mulching with wheat (Triticum aestivum L.) residue, and time and depth of flooding on the emergence of the two weed species collected from Nanjing, China. Light strongly increased seed germination. Under dark conditions, E. crus-galli seed germination (85%) was higher than that of E. colona (70%). The seeds of both species exhibited the greatest germination (90% for E. crus-galli and 80% for E. colona) when sown on the soil surface, and emergence decreased with increasing soil burial depth. Burial depths of 2.2 and 1.4 cm reduced seedling emergence by 50% for E. crus-galli and E. colona, respectively. No emergence was found at a depth of 6 cm. The seedling emergence for E. colona was lower than for E. crus-galli at the same soil burial depth. Mulching with wheat residue considerably reduced the seedling emergence and aboveground biomass of both species. The inhibitory effect of mulching with wheat residue on E. colona was more notable than on E. crus-galli. Early and deep flooding significantly suppressed the emergence, height, and biomass of E. crus-galli and E. colona, especially E. colona. The results gained from this study could provide fundamental ecological knowledge for managing Echinochloa species in direct-seeded rice systems.