Weed infestation and its influences on early growth of rice (Oryza sativa) in flooded plains of savanna in northern Ghana.

This paper reports collaborative research on the development of low input and sustainable rice production technology in flooded plains of lowland savanna in northern Ghana. The research aims are to identify suitable weed management methods. Weed infestation and its influence on rice plants (Oryza sativa c.v. Sikamo) at early growth stage were investigated in rainfed and broad-casted rice fields in Yipielgu (Y) and Zaw (Z) villages where submergence conditions were different. At March before plowing, Paspalum scrobiculatum, surviving the dry season, were dominant, accounting for 50 to 97 percent of dry matter weight (DMW) of weeds. At 45 days after removing weeds and broad-casting, DMW per m 2 was 96.1g in Z under insufficient submergence and 139.5g in Y flooded with around 5 cm depth, respectively. Dominant species were P. scrobiculatum and Digitaria sangunalis. in Z, and Cyperus spp., Fimbristylis spp. and Acroceras zizanoides in Y. DMW of rice plants decreased as total DMW of weed increased above 150g/m 2 approximately in Y, while it was not clear when total DMW was below 150g/m 2 in Z. Glyphosate applied before plowing or after broad-casted could not suppress weeds both in Z and Y. It is needed to determine appropriate application time and rate of non-selective herbicides for effective management of weed in rice fields in northern Ghana.