impact of split application of different n-fertilizer sources on weed growth, safflower yield, and nitrogen use efficiency

A 2-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 ((1/4,3/4,0), (1/3,1/3,1/3), (1/2,1/2,0), and (1/3,2/3,0)) on weed growth, safflower (carthamus tinctorius l.) yield, and n use efficiency (nue), using a split splitplot design with three replications, at the experimental research station of shiraz university, in 2015 and 2016. in weedy plots, applying anfertilizer in a split pattern of 1/2,1/2,0 (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 5% compared to ufertilizer and similar split pattern. in weed free plots, the highest seed and oil yields (3303.52 and 753.09 kg ha1, respectively) were achieved by an and ufertilizers in a split pattern of 1/2,1/2,0. applying an fertilizer and split patterns of 1/3,2/3,0 (one third of n at sowing and two thirds at stem elongation) and 1/4,3/4,0 (one quarter of n at sowing and three quarters at stem elongation) maximized safflower nupe (0.78 kg kg1). applying u fertilizer and split pattern of 1/2,1/2,0 increased safflower ability to compete vs. weeds up to 20% compared to anfertilizer. overall, in order to improve safflower yield and nue and control weed, applying ufertilizer and split application of 1/3,2/3,0 or 1/4,3/4,0 can be suggested as a component of integrated weed management programs.