Competitiveness of semidwarf upland rice cultivars against palisadegrass (Brachiaria brizantha) and signalgrass (B-decumbens)

When savannas in Latin America are brought into cultivation, rice (Oryza sa tiva L.) can be sown with the perennial grasses palisadegrass [Brachiaria b rizantha (Hoechst. ex A. Rich) Stapf] and signal grass (B. decumbens Stapf) to harvest a grain crop while establishing a pasture to suppress weeds and provide grazing in subsequent years. However, these Brachiaria spp. can re duce upland rice yields. Rice cultivars need to be competitive with Brachia ria spp. to maintain yields but must allow Brachiaria spp. sufficient growt h for pasture establishment. Field studies were conducted during 1994 and 1 995 on a Typic Haplustox oxisol soil in the Eastern Plains of Colombia to e valuate the competitiveness of upland rice cultivars and to identify rice t raits for competitiveness. Ten (1994) and 14 (1995) upland rice cultivars w ere grown with and without signalgrass in 1994 and palisadegrass in 1995. R ice cultivars differed substantially in their competitiveness. Rice yield l osses ranged from 18 to 55%, and Brachiaria aboveground biomass ranged from 1.4 to 3.2 Mg ha(-1) dry mass. Competition for light was critical, rice ph oton flux density interception, leaf area index [greater than or equal to 4 5 d after emergence (DAE)], and number of tillers (greater than or equal to 60 DAE) were correlated with competitiveness. No tradeoff between high yie ld potential and competitiveness was detected in these upland rice cultivar s. Early maturity of rice is a desired characteristic for the rice-Brachiar ia spp. association. The development of more-competitive cultivars appears to be a viable approach for reducing herbicide dependency and improving pro fitability of Latin American rice-pasture intercropping systems.