Effect of redroot pigweed (Amaranthus retroflexus L.) interference on corn (Zea mays L.) yield quantity and quality under different irrigation and nitrogen levels

A field experiment was conducted during 2010 and 2011 to determine the influence of redroot pigweed (Amaranthus retroflexus L.) on corn yield quantity and quality under different irrigation and nitrogen levels. Experimental treatments were arranged in a randomized complete block design with a split factorial arrangement of treatments in four replications. The main plots were subjected to irrigation treatments consisted of: low (Lir) and full (Fir) irrigation regimes. The subplots attributed to a factorial combination of four N rates (0, 150, 300 and 450 kg N ha-1) and two levels of redroot pigweed interference with corn (weed free, C; and weedy, CP). The results revealed that positive effects of N on corn grain yield increased by water availability enhancement and adversely decreased in water deficiency conditions. In weed infested conditions, when the moisture was sufficiently supplied (CP-Fir treatment), enhancement of applied N up to 300 Kg N ha-1 significantly increased corn grain yield. On the contrary, in low irrigation regime with weed interference (CP-Lir treatment), different N rates did not have significant effect on corn grain yield. By contrast, redroot pigweed positively responded to enhancement of applied N especially in full irrigation regime and increase in each level of applied N resulted in significant increment of pigweed seed yield. Also, the results indicated that more N was applied, more corn grain yield loss due to weed interference was observed in both irrigation regimes. Finally, based on the information gained in this study we cannot recommend increasing inputs (water and N), especially in sandy soils, to diminish the redroot pigweed/corn competition and in terms of corn yield and environment protection.