Seed bank dynamics and emergence pattern of weeds as affected by tillage systems in dry direct-seeded rice

The vertical weed seed distribution in the soil and the emergence pattern of weeds have implications for weed management in different cropping systems. Various agronomic practices have been reported to influence these factors, and tillage has a great role to play in weed management strategies. The effect of conventional tillage (CONT) and zero tillage (ZT) on the distribution of weed seeds in the soil, and the emergence pattern of different weed species was evaluated in dry direct-seeded rice in the summer (kharif) seasons of 2012 and 2013. The ZT system resulted in a higher proportion of weed seeds in 0-2 cm of the soil layer at the time of crop sowing, with 48-52% of broadleaved and 45-55% of grassy weed seeds; whereas, CONT had weed seeds buried in deeper layers, with 47-48% of broadleaved and 50-55% of grassy weed seeds in the lowermost layer (5-10 cm). At crop harvest, both tillage systems showed higher proportions of weed seeds in the upper 2 cm of the soil layer; however, this was due to seed shedding of mature weeds on the soil surface. The maximum emergence of Cyperus rotundus and Echinochloa colona was 33-42% and 20-26% higher in ZT than CONT. In 2012, Cyperus compressus emergence in ZT exceeded CONT by 65%, whereas Echinochloa crus-galli and Dactyloctenium aegyptium emerged 22% and 52% more in the CONT system than ZT. The emergence pattern of Digitaria ciliaris was not influenced by tillage systems. The information from this study will facilitate better decision making in weed management through the integration of tillage systems and other weed control measures in dry direct-seeded rice.