To evaluate the effects of nitrogen and herbicide on spatial distribution and variability of broadleaf weed patches, this experiment was conducted in 2005 at the Agricultural Research Station, Ferdowsi University of Mashhad. As a result of factorial arrangement of Nitrogen fertilizer amount (25 and 120 kg ha-1), Nitrogen fertilizer time of application (Whole application at the time of corn planting and equal split application at the time of corn planting and at six-leaf stage) and weed control (applying or not applying herbicide), eight treatments were assigned to eight fields each of which 10m wide and 30m long. Weed sampling was taken at 264 points at each corners of 2.5 by 2.5m grids and reported four times during growing season, with 23days interval, beginning before top dressing fertilizer and herbicide in related plots (June, 24th). On the whole, 12-15 weed species were observed in different
treatments. At first sampling, weed populations mainly consisted of annual broadleaf species, such a way that 2-3 species were grasses and the others were broadleaf weeds. In early growing season prostrate pigweed was dominant weed in all treatments followed by common lambsquarters, black nightshade and common purslane, respectively. A pronounce weed reduction was observed in herbicide treated fields mainly due to reduction of broadleaf weed populations and mean density and relative density percentage were also decreased by the end of growing season. At second sampling, the broadleaf populations were almost the same in herbicide treated fields and N2 application did not effect on herbicide efficacy. In the non-herbicide treatments, the total and broadleaf weeds density were increased primarily but decreased later in the growing season. Broadleaf weeds mapping showed high
level of weed infestation in all treatments. Nevertheless, variation range of density in the field was high and the declines of high-density spots from center toward the margin of the patches were observed. The results of this study indicated that spatial distribution could be interpreted as main factor in decision making of weed managements. |
