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Neste trabalho foi avaliada a influência de exsudados radiculares e de extrato aquoso da parte aérea de Ambrosia artemisiifolia na germinação, no vigor de sementes e no crescimento inicial de milho e soja. Foram realizados dois ensaios, o primeiro em esquema fatorial (2x2), milho e soja com e sem exsudato radicular, e o segundo em esquema fatorial (2x4), milho e soja nas concentrações de 0, 25, 50 e 75 % de extrato aquoso de parte aérea de A. artemisiifolia. O exsudato radicular de A. artemisiifolia afetou negativamente o vigor de sementes de milho, mas não a germinação. O exsudato radicular de A. artemisiifolia não influenciou a germinação nem o vigor de sementes de soja. A cultura do milho apresentou maior sensibilidade que a soja ao exsudato radicular. O extrato aquoso da parte aérea de A. artemisiifolia afetou negativamente o vigor de sementes de milho e o vigor e a germinação de sementes de soja, sendo a soja mais sensível aos efeitos alelopáticos do extrato. O extrato aquoso da parte aérea de A. artemisiifolia apresentou teor de fenóis totais de 11,13 mg g-1 de biomassa seca da parte aérea, o que pode ser considerado um valor alto quando comparado ao de outras infestantes.

Background: Substantial losses to crops can occur due to the presence of sourgrass in agroecosystems, which is promoted by its seed dispersal ability. Environmental factors can affect sourgrass germination and emergence. Objective: The objective of this study was to determine the effects of water restriction, salinity, and depth of sowing on the sourgrass germination and emergence processes. Methods: Experiments using sourgrass seeds were conducted under controlled conditions simulating osmotic and saline stress and seeding depths. The data collected was submitted to analysis of variance and adjusted to models by regression analysis. Results: Smaller osmotic potentials reduced germination, normal seedlings, and increased quiescence, with no germination occurring from-0.80 MPa. Salinity caused a decrease in germination from 20 mM NaCl, influencing the percentage of normal and abnormal seedlings and quiescent seeds. Seed depth influenced the emergence of seedlings, with the maximum percentage of emergence (83%) in the seeds placed on the substrate surface. The maximum depth from which sourgrass seedlings emerged was 7.6 cm. Conclusions: The results lead to the conclusion that the sourgrass germination process tolerates low osmotic potentials and salinity levels. Despite being small sized seeds, they can emerge from high depths. These characteristics justify its occurrence in several regions and agroecosystems, especially in perennial and no-till crops lacking soil cover.

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