Effect of tillage systems and herbicides on weed emergence, weed growth, and grain yield in dry-seeded rice systems

Farmers in many Asian countries are moving from puddled-transplanted rice to dry-seeded rice systems. Dry-seeded rice can be sown after land preparation or under zero-till conditions. Weeds, however, are the major constraint to the production of dry-seeded rice. A study was conducted during the wet season of 2011 and dry season of 2012 at the farm of the International Rice Research Institute to evaluate the effect of tillage systems (zero-till and conventional tillage) and herbicides on weed emergence, weed growth, and grain yield in dry-seeded rice systems. In the zero-till system, the densities of Digitaria ciliaris, Eleusine indica, Eclipta prostrata, and Ludwigia octovalvis increased many-fold from the first season to the second. The efficacy of herbicides (oxadiazon followed by fenoxaprop+ethoxysulfuron and oxadiazon followed by penoxsulam+cyhalofop) was lower in the zero-till system than in the conventional tillage system. Grain yield in the herbicide-treated and weed-free plots was similar between the tillage systems and this response was consistent during both the seasons. However, grain yield in the zero-till-control (one hand-weeded) plots was lower (0.9-1.5tha -1) than in the conventional tillage-control plots. The information gained from this study suggests that yields in zero-till systems similar to those in conventional-tilled systems can be achieved if weeds are effectively controlled. In the absence of effective weed control, zero-till systems may result in poor grain yield