Structure of weed communities occurring in pea and wheat crops in the Rolling Pampa (Argentina)

Companion weed species in wheat and pea crops are influenced by the physiology, canopy structure, and management practices of these crops. Pea and wheat fields were surveyed in the central Rolling Pampa to compare the weed communities, and to determine the association among weed community structure, crop management practices, and yield. The floristic and functional structure of weed communities was evaluated for species richness and abundance. Floristic groups and their relationships with crop yield and management were analysed using multivariate methods. The weed community of pea crops was more diverse than that of wheat crops at both regional and field scales. Alpha diversity was 20 and 13 for pea and wheat, respectively, while gamma diversity was 91 for pea and 64 for wheat. In both crops, the structure of the weed communities was related to yield, chemical control practices, fertilization and the previous crop. Crop dominance, as accounted by crop growth and herbicides effects, was the main factor defining the weed community structure. Fertilization and previous crop had a secondary effect. Similar proportions of dicotyledonous and monocotyledonous species occurred in both crops, probably because of climatic factors operating at regional scale.