Barley (Hordeum vulgare L. ‘Advance’) and wild oat (Avena fatua L. # AVEFA) were grown in the field in monoculture and mixed culture (additively) to compare their seasonal growth and development. Barley and wild oat tiller and tiller head production were reduced by the interference (higher density) of the other species. Plant height of either species was not affected by interference of the other. Wild oat biomass was reduced more and at an earlier growth stage (two to three tillers) than was barley biomass (heading) in mixed culture. Barley and wild oat grown in monoculture had similar total plant nitrogen content throughput the growing season. Gas exchange and water potential of barley and wild oat in monoculture and mixed culture were similar. All measurements indicated that barley and wild oat grown in monoculture had growth and development patterns that were similar. In mixed culture, however, barley was more competitive with wild oat than wild oat was with barley. Wild oat reduced barley yield component quality and grain yield.
