Competition of weeds with upland rice in Ouro Preto D'Oeste, RO, Brazil.

Abstract

In Rondonia, weeds constitute one of the principal factors of annual crop production limitation. In order to determine the critical competition time of weeds with upland rice (Oryza sativa L.), one experiment was carried out at Ouro Preto D'Oeste, RO, Brazil, from December 1985 to March 1986, on a red-yellow podzolic soil. lts design was in randomized blocks with 14 treatments replicated four times and the crop was carried on with and without weeds for different periods. The cultivar used was IAC 164 sowed in lines spaced 0₂5 m and 50 seeds/m linear. The populacional density of weeds rand from 250 to 300 plants/m². The main species of weeds observed on the experimental area were crabgrass (Digitaria sanguinalis (L.) Scop.), alexandergrass (Brachiaria plantaginea (Link.) Hitch), garden spurge (Euphorbia pilulifera L.), gripeweed (Phyllanthus niruri L.) and Junglerice (Echinochloa colonum (L.) Link.). The competition period decreased the height of rice plants, number of panicles per m² and grain yield; however, the weight of 100 seeds was not affected. The critical competition period occurs between 30 and 60 days alter seedling emergency. The former competition period was of 30 days, while the total competition period was of 60 days after seedling emergency.