Environmental Factors Influencing Seed Germination and Seedling Emergence of Cyperus iria

Weeds are often the principle biotic constraint to paddy crop production reducing paddy yield by about 15–21 % globally and by 20- 40 % in Sri Lanka. The existing climatic factors are highly favourable for the growth of many weed species, which offer competition with paddy. Mature viable seeds of Cyperus iria, randomly collected from paddy fields in the five districts of t he Northern Province of Sri Lanka, were used to assess the impact of selected environmental parameters and agronomic practices on their germination and seedling emergence. The weed seeds from different districts were subjected to four combinations of day/night temperatures coupled with three light durations in a Completely Randomized Designs as a two-factor factorial experiment. The temperature x light duration interaction with the highest seed germination was combined with different flooding heights and durations, followed by soil-burial depths. The frequencies of seed germination and seedling emergence were analyzed using the Chi-square test in SAS 9.1 software (P=0.05). C. iria seeds from Vavuniya recorded the highest seed germination at all combinations of day/night temperature and light durations, while the lowest was recorded from Jaffna. Seed germination was the highest at day/night temperature 35/30 °C and the lowest at 25/20°C (P<0.05). The highest frequency of seed germination was observed i n 24 h light and the lowest in 24 h dark, under all day/night temperatures. Flooding 5 days after sowing (DAS) at a height of 5 cm showed the lowest seedling survival measured at 28 DAS (P<0.05). The seedling emergence of C. iria was restricted (P<0.05) at soil burial depths of 2.5 cm and 5 cm. The results revealed that 25/20°C day/night temperature s in 24 h darkness, seed burial >1 cm soil depth, and flooding at 5 cm height from 5 DAS suppressed C. iria seedling emergence and growth.