The critical period of weed infestation in soybeans takes up to 4 weeks after emergence, and after this period, the yield decreases. The duration of weed competition and crop has no statistical significance on the 1000 kernel. However, weeded out plots had slightly higher weight and it ranged from 145.99 g to 161.13 g and weedy plots had on average a lower weight of 124.26 g to 144.28 g. Average number of pods per plant shows a similar trend as in grain yield. A higher number of pods per plant, and thus higher yield will be achieved within 4 weeks from germination. Length of weediness had no influence on the height of soybean plants. The average height of soybeans ranged from 92 to 138 cm and was not statistically significant. The average number of branches of soybean was also not influenced by the different lengths of weedy or there hasn't been noticed any regularity. Only number of articles of soybean coincides with the length of the critical period of weed infestation for 4 weeks from germination of soybean when it comes to the pronounced influence of weed competition on crop. On the plot where the weed flora developed undisturbed throughout the growing season was determined 1680.25 g of plant mass per m2. In contrast, on weeded plots emerged weeds at the end of the season they had a very lightweight, only 7 g. Most significant mass loss of weeds happened within the first 4 weeks of the eruption of crops, suggesting that the maintenance of crops free of weeds within the first 4 weeks is necessary for the achievement of high and stable yield.