Effect of NP supply on herb yield, hypericin content and cadmium accumulation of St. John's Wort (Hypericum perforatum L.)

The experiment was done on 'Topas' cultivar in the Research Station of Tarbiat Modarres University located near Tehran and was conducted through two successive seasons of 1998-1999. We have studied the effect of three levels of nitrogen fertiliser (0, 150, 250 kg ha(-1)) and three levels of phosphorous fertiliser (0, 100, 200 kg ha(-1)) on herb yield, hypericin content and cadmium accumulation of the plant. Results show that fertiliser treatments can affect herb quality and yield. The highest herb yield (1053.9 g m(-2)) was produced in the plots that received 250 kg N and 100 kg P fertiliser as compared to control plot(745.8 g m(-2)). According to the results NP-supply increased the number of flowering stems per plant and hypericin content. There is a significant correlation between the number of flowering stems and the hypericin content of the St. John's wort herb. All fertiliser treatments increased cadmium accumulation of the herb as compared to the control treatment. The highest cadmium content (0.269 mg kg(-1) dry weight basis) was measured in the plot that received 250 kg N and 200 kg P fertiliser, the lowest cadmium content was measured (0.091 mg kg(-1) dry weight basis) in the control plot.