The Responses of Corn Weeds to Nitrogen Fertilizer Rates and Herbicide Dosages

To evaluate the interaction of nitrogen rates and Nicosulfuron dosages on corn weeds and corn yield, a factorial experiment based on randomized complete blocks design was conducted at Research Fields of University of Tehran in 2009. The nitrogen application rates were 0, 180, 270 and 360 kg ha-1 with nicosulfuron herbicide being applied at 0, 20, 40, 60 and 80 g ai ha-1. Each treatment combination was replicated three times. The result illustrated that all weed spices, except Russian Knapeweed (Acroptilion repens) showed a positive response to the highest level of nitrogen fertilizer (i.e 360 kg ha-1) where weeds dry weights increased markedly. The lowest weed biomass production was observed with herbicide dosages of 60 or 80 g ai ha-1 and nitrogen application rate of 180 or 270 kg ha-1. The more nitrogen fertilizer used (i.e. 360 kg ha-1), the higher herbicide dosages needed to effectively control the weeds as more resource might be available for their growth. The responses of corn yield to N rate and herbicide dose were similar to those of weeds as there was a close relationship between weed biomass productions and corn yields. Overall, given the economical costs and environmental consequences of fertilizer and herbicide applications, one may recommend a N application rate of 270 kg ha-1 with 60 g ai ha-1 nicosulfuron in terms of both acceptable weed control (almost 85%) and obtaining a high corn yield (almost 11000 kg ha-1).in additional to achieve 11000 kg ha-1 should use 180 kg ha-1 N fertilizer with 70 g ai ha-1 or 360 kg ha-1N fertilizer with 80 g ai ha-1.