Thirty-six years of no-tillage regime altered weed population dynamics in soybean

Changes to tillage practices can impact weed species composition and population dynamics in arable fields. The objective of this study was to evaluate and compare the impact of long-term (36 yr) no-tillage (NT) and conventional-tillage (CT) systems on weed species composition, density, seedling emergence, and diversity, in a continuous soybean [Glycine max (L.) Merr.] system in Southeast Texas. Results from 2016 and 2017 observations showed that weed species composition varied between CT and NT, and the total density was greater in NT (14 and 86 plants m^–2 for summer and winter annuals, respectively) compared to CT (3 and 45 plants m^–2, respectively). Moreover, tall waterhemp [Amaranthus tuberculatus (Moq.) Sauer], prostrate spurge [Chamaesyce humistrata (Engelm. ex Gray) Small], and red sprangletop [Dinebra panicea (Retz.) P.M. Peterson & N. Snow] emergence was delayed in NT compared to CT. Vertical distribution (70-cm depth) of viable weed seeds in the soil profile was also influenced by tillage regime; greater proportion of weed seeds were present on the soil surface (0–5 cm) in NT (57–80% among different species) compared to CT (38–56%). However, weed diversity indices did not differ between CT and NT. Results indicate that long-term NT, even with herbicide management, can lead to greater weed densities with a shift towards small-seeded annual species (common purslane [Portulaca oleraceae L.], parsley-piert [Aphanes arvensis L.], cutleaf groundcherry [Physalis angulate L.]). Growers transitioning to NT should be cognizant of potential changes to weed population dynamics as a result of altered tillage regime and devise strategies for effective management.