It was conducted field trials with cultivars Santa Rosa e IAC-2 in two soils, "Latossol Roxo" and "Dark Red Latossol - sandy phase", at Jaboticabal, São Paulo State, with the objective to stud y the role of weed competition period on some soybean morphological parameters and contents of protein, ether-extract and ash in the grains. The experimental design used was the randomized block, when the cultivars were kept with and without weed competition since the emergence for periods of 0, 10, 20, 30, 40, 50 and 60 days. Based on the results, it may be concluded that a short initial period (20-30 days) free of weed competition, was enough to avoid negative effects, in the final plants height, shoot diameter and height of inferior pod insertion, and on the other hand to keep the protein, ether-extract and ash content at normal level in both culti vars and soils studied.
Weed competition periods; soybean; morphologycal parameters; grain composition