Crop establishment options for lowland irrigated rice in relation to weed infestation and grain yield

M. Azmi and D.E. Johnson

Abstract

Field experiments were conducted over three consecutive seasons to determine the effect of crop establishment methods on rice yield and weed growth. The options included wet seeding (WS), dry seeding (DS), drum seeding (WDS), seedling broadcasting (BCS), water seeding (WTS) and manual transplanting (TPR). Population densities of weedy rice were substantial (mean density 35  panicles/m2) in the main season 2005/06 but considerably lower in off season 2006 and main season 2006/07. Across seasons, in the unweeded plots, weeds caused 37% rice yield loss and there were no significant interactions with establishment method. In the three seasons, rice yields from BCS did not differ from TPR under weed free condition. In each season, the lowest yields were from DS. In off season 2006, yields from WS and WTS were not different from TPR and BCS and in main season 2006/07, yields from WS, WDS, WTS, TPR and BCS were almost similar. In the main season 2005/06, weedy rice infestations were highest in the DS and WS and in these treatments panicle densities of weedy rice were more than twice those in BCS and almost three times those in WTS. In the subsequent seasons weedy rice infestations were much lower, irrespective of treatments. Weed dry weights recorded in the unweeded plots in the off-season 2006 and main season 2006/07 revealed weed growth to be greatest in DS followed by WS and least in WTS. Water seeding, or the broadcast of pre-germinated seed into standing water (5–10 cm deep), significantly reduced weedy rice populations and other weed growth compared to DS or WS and gave yields that were comparable to TPR in two out of three seasons. Where water supplies are adequate, with soils having low infiltration rates and well-levelled fields, WTS appears to be an effective method of crop establishment to address the problems of serious weedy rice or grassy weeds infestations.

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