Structure of weed communities occurring in monoculture and intercropping of field pea and barley

Weed growth suppression is an explanation of intercropping yield advantage, which can be applied to diminish herbicide use in agriculture. Intercrop effects on weed community structure, nonetheless, have been sparsely studied. The hypothesis that intercrops will produce greater changes in weed community structure than monocultures was therefore postulated. It was concurrently predicted that species diversity of the weed community will be lower in the intercropping than in the monocultures, and that winter- and spring-emerging species in intercrop will be relatively less and more abundant than in monocultures, respectively. Field experiments were carried out at Buenos Aries and Rojas (Argentina) involving monocultures, intercrops of barley and pea, and a control treatment where weeds grew without crops. Effects on weed communities were characterised in terms of growth, species diversity (richness and evenness), and floristic and functional composition. Nitrogen content of plant biomass and interception of solar radiation were also measured. The greater the crop biomass, the higher the weed suppression was. However, barley tended to greatly suppress the growth of weed and pea plants, which could be explained by the greater nitrogen accumulation in barley plants in monocultures and intercrops. Furthermore, there were apparent complementarity in nitrogen uptake between barley and pea when intercropped, since both crops use different sources of soil nitrogen. Intercrops and barley monocultures generally produced similar effects on the companion weed communities, whereas pea effects were less suppressive and more variable. However, intercrops effects appeared to be more stable across experiments. Spring-emerging species generally increased its relative importance in the intercrop weed communities; whereas winter-emerging species were usually less abundant in intercrops. Divergence in the abundance of winter and summer emerging weeds could be attributed to the different canopy dynamics of intercrop and monocultures. This work contributes to improve current understanding of how crop–weed communities are assembled and may help in developing weed management practices that are environmentally sound.