Implications of narrow crop row spacing and delayed Echinochloa colona and Echinochloa crus-galli emergence for weed growth and crop yield loss in aerobic rice

Field experiments were conducted in 2008 and 2009 to determine growth and seed production of Echinochloa colona and Echinochloa crus-galli emerging at five intervals (0, 15, 30, 45, and 60 days after rice emergence, DARE) in aerobic rice seeded at 20- and 30-cm row spacing. Plant height of these two weed species was not influenced by the crop row, but it was influenced by the weed emergence time. Weeds of either species emerging until 30 DARE had greater biomass and more seeds under wide rows than under narrow rows, but row spacing had no effect on biomass and seeds of plants emerging later. In both crop row spacing treatments, delay in weed emergence until 45 DARE significantly reduced weed biomass. E. colona and E. crus-galli plants that emerged 60 DARE produced only 3 seeds plant(-1) in 30-cm rows, whereas no seed was produced by these plants in 20-cm rows. Fitting a single linear function to the combined data for rows and weed emergence time gave a strong positive linear relationship between shoot biomass (g plant(-1)) and seed production (number plant(-1)) of these species, accounting for 94% and 93% variation in E. colona and E. crus-galli. respectively. These relationships can be used as a predictor of seed production in these species. Regardless of the weed species and weed emergence date, rice grain yields were greater in narrow rows than in wider rows. In the case of both weed species, rice grain yield improved significantly with each delay in weed emergence up to 45 DARE. The results of this study suggest that narrowing row spacing and controlling early weeds led to decreased weed growth and seed production, and increased grain yield in aerobic rice. Narrow crop row spacing and early weed control could be important components of integrated weed management strategies in aerobic rice. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.