The aim of this work was to analyze the growth and the development of five weeds of the Amaranthus genus, under non-competitive conditions. The studied species were: A. deflexus, A. hybridus, A. retroflexus, A. spinosus and A. viridis. Eight periodic evaluations of growth were taken, every 10 days, starting at 20 Days After Seeding (DAS). The variables evaluated per plant were: leaf area; roots, stems, leaves, flowers + fruits and total dry weight; obtaining, from the last variable, the absolute and relative growth rates. The phenologyof the plants was also evaluated. A. deflexus was the species with the shortest vegetative cycle , and with the lowest accumulated dry weight and leaf area; whereas A. retroflexus and A. hybridus were the species which reached the highest values for these variables. A. viridis presented the best ecological adaptability for the conditions of the experiment: it showed fast vegetative development and absolute growth rate, and high accumulation of dry weight and leaf area. These results suggest that A. viridis is a species with high potential to interfere in the agricultural crops, due to the efficient use of the growth resources available by the ambient during its initial growth stages.
Pigweed; competition; dry weight; leaf area
