Crop-Weed Competition in Direct Seeded Low Land and Upland Bunded Rice¹

Echirtochloa arus-galli and E. catonum were the predominant grass weeds in lowland and upland bunded rice, respectively. These weeds competedwith rice at all stages. Among sedges, Cyperus difformis was ihe major weed and its competition was severe in early stages under low land conditions Cyperus iria was Ihe most predominant weed both under low land and upland bunded rice, while Ammannia baccifera and Marsilea quadrifoliata were present only under lowland conditions. During monsoon and summer seasons, an unchecked weed growth in low-land rice caused 53% reduction in grain yield, while under upland bunded rice the extent of yield reduction was about 91%. In order to obtain higher yield in lowland, the rice crop should be kept free from weeds during the first 50 days in monsoon season and 30 days in summer seasons. In upland bunded rice, a weed-free situation of 60 days in monsoon and 70 days in summer was found essential.