Periods of weed interference in soybean under tillage and no-tillage

This work aimed to determine the interference of weed communities in crop yield characteristics, under no-till and conventional till systems. The soybean cultivars used in these experiments were M-SOY - 6101 and CD 201 for conventional and no-till, respectively. The no-till system weed community reached its maximum value of 377 plants m(-2) 28 days after soybean emergence. Maximum dry matter accumulation was 365.7 g m(-2), 118 days after emergence, with the main plants being Alternanthera tenella, Cenchrus echinatus and Bidens pilosa. Under the conventional till system, maximum density was 161 plants m(-2), 18 DAE and 406.7g m(-2) of dry matter accumulation at 118 DAE, with the main plants being A. tenella, Senna obtusifolia and Panicum maximum. Accepting losses of 5% in soybean productivity, the CPPI values were estimated to range from 33 to 66 DAE for the no-till system and from 34-76 DAE for the conventional till system. Weed interference during the full crop cycle reduced, in average, 46 and 32% of productivity under the no- till and conventional till systems, respectively. No effects were observed on plant height, first pod insertion height, and number of pods per plant due to the presence of weed community.