EFFECT OF NITROGEN RATES ON CRITICAL PERIOD FOR WEED CONTROL IN POTATO

The critical period for weed control (CPWC) is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. A field research was conducted in 2007 in Ardabil, Iran, to evaluate the effect of nitrogen rates on critical period for weed control in potato. Nitrogen fertilizer was applied at rates equivalent to 0, 100 and 200 kg N ha-1. A quantitative series of treatments of both increasing duration of weed interference and length of weed-free period (0, 20, 40, 60 and 80 DAE) were imposed within each nitrogen main plot. Application of 200 kg N ha-1 reduced weed density and increased weed dry mass compared with non-application of nitrogen. Results showed that the addition of 100 kg N ha-1 delayed the beginning of the CPWC in potato when compared with the 0 and 200 kg N ha-1. The duration of CPWC in potato also decreased when 100 kg N ha-1 was applied. Maximum values for potato yield was recorded in weed free plots and100 kg N ha-1. Practical implications of this study are that 100 kg N ha-1 could have been improving potato compatibility for weed control more than 0 and 200 kg N ha-1.