Amaranthus quitensis population dynamics. Influence of chemical and mechanical treatments in a soybean crop

Abstract

Trials have been conducted during 1986/87 and 1987/88 in order to describe the effect of different agronomic practices on pigweed (Amaranthus quitensis) population dynamics. Seedling recruitment, emergence fluxes, seedling survival, fecundity, initial and final seed banks and the annual rate of growth of the populations (l) with the two latter parameters were evaluated. Three pigweed emergence cohorts were evaluated. Seed production was only observed in first and second cohorts. First cohort contributed with higher density and greater number of seeds. Crop presence did not remarkably affect any of the parameters considered. The l increased on overage 53% in absence of the crop and 50% in presence of the crop when no chemical control and cultivation were performed. When a cultivation was done l increase oscilated between 9 and 20% depending on the year. When herbicides were used l show a population increase of 9% for postemergence applications and 28% for preemergence aplications.