Changes in competitive ability between safflower-weeds affected by timing of nitrogen fertilizers

Abstract

Nitrogen (N) effects on crop-weed competition and its information may help to improved integrated weed management systems. A two-year field experiment (2015 and 2016) was conducted on a silty clay loam soil in semi-arid climatic conditions to determine the combined effects of N sources (ammonium nitrate (AN), ammonium sulfate (AS), sulfur coated urea (SCU), urea (U)) and timing fertilization (sowing, stem elongation, flowering) on weed-safflower (Carthamus tinctorius L.) competition and safflower yield at Shiraz University, Iran. The experimental design was a split split-plot with three replications. Results showed that weeds significantly reduced safflower yield components approximately 39% and caused a decrease in seed yield up to 70%. In weed free, the highest seed yield (3303.52 kg ha-1) and oil yield (753.09 kg ha-1) were achieved by AN and U fertilizers, respectively, when N fertilization was applied half (50 kg N ha-1) at sowing and other half (50 kg N ha-1) at stem elongation and zero N application at flowering stage (T1N1/2, T2N1/2, and T3N0). However, ANor U fertilizer timing of T1N1/2, T2N1/2, and T3N0 increased relative competition intensity (RCI) and ability to withstand competition (AWC) indices approximately 80%. On the contrary, U fertilizer timing of T1N1/2, T2N1/2, and T3N0 increased ability to compete (AC) index up to 20% as compared to the AN fertilizer. Our research has shown that U fertilizer timing of one third of the N (33.5 kg N ha-1) fertilization at sowing, two thirds of the N (66.5 kg N ha-1) fertilization at stem elongation and zero N application at flowering (T1N1/3, T2N2/3, and T3N0) can be used to advise farmers of the importance of strategic fertilizer management in terms of both weed management and safflower yield.