Response of Corn and Redroot Pigweed to Nitrogen Fertilizer in Different Irrigation Regimes

The effect of irrigation regimes and N rates on corn ( Zea mays L.) yield and redroot pigweed ( Amaranthus retroflexus L.) growth in sandy soils is not completely understood. Therefore, field experiments were conducted in a semiarid region of Iran in 2010 and 2011 to determine the influence of N rates and irrigation regimes on corn and redroot pigweed leaf area index (LAI), dry matter and grain yield, N uptake, irrigation water productivity (IWP) and N leaching loss. The experiment was conducted using a randomized complete‐block design with a split‐factorial arrangement of treatments in four replicates. The main plots were subjected to either a low (L) or a full (F) irrigation regime. The subplots were arranged in a factorial scheme with four N rates (0, 150, 300, and 450 kg N ha −1 ) and two levels of redroot pigweed interference with corn (weed free, CW 0 ; and weedy, CW 1 ). The results indicated that the more N was applied, the higher were corn grain yield losses in both irrigation regimes due to weed interference. The difference in corn grain yield between CW 0 F and CW 1 F treatments was 400 and 1800 kg ha −1 at N 0 and N 450 levels, respectively. In contrast, the difference between CW 0 L and CW 1 L reached 300 and 800 kg grain ha −1 at N 0 and N 450 levels, respectively. Based on the information gained in this study, we do not recommend increasing inputs (water and N), especially in sandy soils, to diminish the redroot pigweed/corn competition.