R. Moradi Talebbeigi - Department of Crop Production and Plant Breeding, School of Agriculture, Shiraz University, Shiraz, Islamic Republic of Iran.
S. A. Kazemeini - Department of Crop Production and Plant Breeding, School of Agriculture, Shiraz University, Shiraz, Islamic Republic of Iran.
H. Ghadiri - Department of Crop Production and Plant Breeding, School of Agriculture, Shiraz University, Shiraz, Islamic Republic of Iran.

A ۲-year field experiment was conducted to evaluate the effect of N sources [Ammonium Nitrate (AN), Ammonium Sulfate (AS), Sulfur Coated Urea (SCU), and Urea (U)] and split application ((۱/۴,۳/۴,۰), (۱/۳,۱/۳,۱/۳), (۱/۲,۱/۲,۰), and (۱/۳,۲/۳,۰)) on weed growth, safflower (Carthamus tinctorius L.) yield, and N Use Efficiency (NUE), using a split split-plot design with three replications, at the Experimental Research Station of Shiraz University, in ۲۰۱۵ and ۲۰۱۶. In weedy plots, applying AN-fertilizer in a split pattern of ۱/۲,۱/۲,۰ (applying half of the N at sowing time and the rest at stem elongation) increased weed infestation. This treatment enhanced total weed N Uptake Efficiency (NUpE) up to ۵% compared to U-fertilizer and similar split pattern. In weed free plots, the highest seed and oil yields (۳۳۰۳.۵۲ and ۷۵۳.۰۹ kg ha-۱, respectively) were achieved by AN- and U-fertilizers in a split pattern of ۱/۲,۱/۲,۰. Applying AN fertilizer and split patterns of ۱/۳,۲/۳,۰ (one third of N at sowing and two thirds at stem elongation) and ۱/۴,۳/۴,۰ (one quarter of N at sowing and three quarters at stem elongation) maximized safflower NUpE (۰.۷۸ kg kg-۱). Applying U fertilizer and split pattern of ۱/۲,۱/۲,۰ increased safflower ability to compete vs. weeds up to ۲۰% compared to AN-fertilizer. Overall, in order to improve safflower yield and NUE and control weed, applying U-fertilizer and split application of ۱/۳,۲/۳,۰ or ۱/۴,۳/۴,۰ can be suggested as a component of integrated weed management programs.

Ability to compete index, Fertilizer management, Nitrogen efficiency, Redroot pigweed., شاخص توانایی رقابت, مدیریت کود, کارآیی نیتروژن, تاج خروس