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 sativa L.) can be sown with the perennial grasses palisadegrass [Brachiaria brizantha (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 reduce upland rice yields. Rice cultivars need to be competitive with Brachiaria spp. to maintain yields but must allow Brachiaria spp. sufficient growth for pasture establishment. Field studies were conducted during 1994 and 1995 on a Typic Haplustox oxisol soil in the Eastern Plains of Colombia to evaluate the competitiveness of upland rice cultivars and to identify rice traits for competitiveness. Ten (1994) and 14 (1995) upland rice cultivars were grown with and without signalgrass in 1994 and palisadegrass in 1995. Rice cultivars differed substantially in their competitiveness. Rice yield losses 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 photon flux density interception, leaf area index [greater than or equal to 45 d after emergence (DAE)], and number of tillers (greater than or equal to 60 DAE) were correlated with competitiveness. No tradeoff between high yield potential and competitiveness was detected in these upland rice cultivars. Early maturity of rice is a desired characteristic for the rice-Brachiaria spp. association. The development of more-competitive cultivars appears to be a viable approach for reducing herbicide dependency and improving profitability of Latin American rice-pasture intercropping systems.