COMPETITION BETWEEN MAIZE AND BARNYARD GRASS (ECHINOCHLOA-CRUS-GALLI)AT DIFFERENT MOISTURE REGIME

Competition between a natural stand of barnyard grass Echinochloa crus -galli (L.) P. Beauv. and a maize crop was studied during two years. T he combined biomass of maize and barnyard grass increased with soil wa ter availability. Maize density varied little and its yield was determ ined by individual plant size. Maize shoot weight decreased with incre ase in root biomass of barnyard grass (which is a product of plant num ber per area and individual root weight) and decreasing soil water ava ilability. Barnyard grass density was greatest when the water capacity of soils was low. Root weight and the proportion of dry matter alloca ted to roots (root to shoot ratio) was correlated with individual size of barnyard grass plants. Weight of barnyard grass plants decreased b ut root to shoot ratio increased with decreasing soil water availabili ty. Root competition was the major factor decreasing maize weight whil e above ground competition was of minor importance. With similar above ground biomass, dense stands of barnyard grass consisting of small pl ants with numerous roots caused a greater decrease in maize yield than sparse stands consisting of large plants with fewer roots.