Competition between rice and barnyard grass (Echinochloa). 1. The influence of weed density and nutrient supply in the field

Abstract

In a field trial at Deniliquin, N.S.W., the density of Echinochloa seedlings was found to be inversely related to the final grain yield of rice (Oryza sativa). Echinochloa tillered earlier than rice, and increasing nutrient supply encouraged more rapid tillering. Echinochloa competition reduced the number of rice tillers, panicles, and spikelets per panicle, and these effects were accentuated at high levels of nitrogen and phosphorus application. The percentage of grain filled spikelets was unaffected by increasing Echinochloa density except at high nutrient levels. Superphosphate did not increase the yield of rice, even in the absence of Echinochloa competition. The response by rice to nitrogen was reduced in the presence of barnyard grass. At high weed densities, crop failure resulted when phosphorus and high levels of nitrogen were both applied.