A study was conducted from 2008 to 2010 in Bulgaria to evaluate the weed infestation in field crops, grown in crop rotation by organic farming. Beans cv. Obraztsov chiflik, wheat cv. Yantur, soyabeans cv. Zarya, and winter oats line RS-2 were studied. Two variants were used and foliar fertilization using Humustim in four replications, the size of harvesting plot was 52. 5 m 2. Crop rotation technological schemes were applied according to the requirements of the organic farming without using chemicals. During crop rotation, the density of perennial weeds remained relatively constant. In variants with fertilization by Humustim, the total number of weeds decreased compare to those without fertilization. The lowest density of weed infestation was observed in wintering oats, grown after soybeans-100 pcs. /m 2 and in wheat, grown after field beans-122 pcs. /m 2.
