Study on competitive stress in terms of yield loss caused by pre- and post-submergence weed flora in rainfed lowland direct seeded rice under different seeding densities

摘要

Weed competition reduces the grain yield of rainfed direct-seeded lowland rice drastically. Because it is dry seeded during the end of May or first week of June in coastal Orissa, the field situation in the initial stages is similar to that of uplandwhich hastens the germination and growth of weeds like grasses, some sedges and broad leaf weeds. But with the accunmlation of water in the fields during the months of July and August when the active monsoon, certain specific water tolerant weeds and aquatic weeds (comprising submerged, emerged and floating types) besides wild rices pose problems. These adverse effects can be minimized to a certain extent by maintaining optimum crop stand and canopy development (which can be established by optimum seedrate) in the field which can suppress weed growth.