The Effects of Weed Interference Durations on Phosphorus and Potassium Percentage and Uptake Efficiency of Black Seed (Nigella sativa L.) and its Weeds

One of the most problems in black seed yield reduction is weed interference with this medicinal plant for resources such as macro nutrients. A field experiment was conducted at Agricultural Research Station, Ferdowsi University of Mashhad, Iran, during 2009-2010 growing season. The experiment was laid out in Randomized Complete Block Design (RCBD) with 12 treatments and three replications. Two sets of treatments consisting of weed-infested and weed-free periods were used. In the first set of treatments, weeds compete with black seed until 0, 14, 28, 42, 56 and 70 day after emergence (weed-infested periods). In the second set, plots were kept free of weeds until the mentioned stage (weed-free periods). Results indicated the contents of phosphorus and potassium in weed biomass significantly increased by increasing weed competition durations. However, the percentage and content of phosphorus and potassium in black seed biomass significantly showed a decreasing trend as the weed-black seed competition periods increased. Weed interference with black seed for full growth season decreased contents of phosphorus and potassium in black seed biomass more than 7 and 8 times, respectively. In addition, effects of weed-free and weed-infested periods on decreasing uptake and phosphorus and potassium use efficiency in black seed were significant. Reduction in phosphorus and potassium uptake efficiency of black seed was indicating weak competitiveness of this medicinal plant with its relative weed community.