2016 Volume 61 Issue 1 Pages 1-8
Proper control of barnyardgrass for direct sowing in flooded paddy rice cultivation in Japan’s cold regions requires knowledge of the relation between barnyardgrass seed emergence characteristics and paddy field water conditions after rice seeding. Barnyardgrass seed emergence characteristics were investigated under submergence conditions. Seeds were collected from paddy rice fields of 13 habitats in Akita prefecture. This study examined two water conditions in plastic containers: submergence and non-submergence. Their respective water depths were 2 cm and 0 cm from the soil surface. Seeds were sown into soil in May and June. The percentage of final emergence was significantly lower for submerged seeds than for non-submerged seeds of four habitats of the May sowing and of one habitat of the June sowing. The average length of days for emergence (ADE) was greater for submerged than for non-submerged seeds from all habitats, irrespective of the sowing time. The value of emergence uniformity (VEU) tended to be greater for submerged than for non-submerged seeds from all habitats, irrespective of the sowing time. For submerged May sown seeds, ADE was delayed 6.2–12.7 days, and VEU was 1.9–3.7 times greater than that of June-sown seeds. Additionally seeds collected from paddy rice fields in three habitats were sown into soil in the pot. Thereafter, the soil was submerged. In the plots, after submergence was ended at 20 and 30 days after submergence, the seed emergence percentage increased, irrespective of the habitat. Results of this study of barnyardgrass demonstrated that submergence causes a loss of emergence uniformity during the emergence period, especially at low temperatures, although emergence can occur under submergence. Furthermore, the cessation of submergence facilitates plant seed emergence.
