Effect of nitrogen and phosphorous fertilizers on the yield and secondary metabolites of medicinal plant Rubia tinctorum L. under salinity conditions

In this study the effect of four levels of nitrogen fertilizer (0, 50, 100, 150) kg/ha and four levels of super phosphate triple (0, 50, 100, 150) kg/ha were investigated on Rubia Inctorum L. (madder) under salinity stress. A factorial experiment was carried out in a research farm in Roaddasht, Isfahan based on complete randomized blocks with three replications. The results of the variance analysis showed that increase in flavonoids content (at 330 nm) was statistically meaningful under various levels of phosphorous fertilizer and interaction of phosphorous with nitrogen (P≤0.01). Flavonoid content was also significantly increased under various levels of nitrogen (P≤0.05). Moreover, the amount of proline in the leaves of madder showed significant variation under different levels of phosphorous, nitrogen, and the interaction of nitrogen and phosphorous at P≤0.01. Also the performance of shoots was significantly affected by different levels of phosphorous and its interaction with nitrogen at P≤0.01. Flavonoids contents at 330 nmwavelength varied between 0.78 to 0.411 nanometer and while the maximum of this flavonoid level was observed under the phosphorous, the minimum was related to 150kg/ha of phosphate and the control (0 kg/ha nitrogen). This suggests that by increase in phosphorous and decrease in nitrogen fertilizers, phenolic compounds are reduced in the plants. The maximum and minimum proline contents were observed under 150 kg/ha nitrogen and phosphorous treatment and control, respectively. The performance of shoots varied ranging from 1.75 to 0.75 kg/m2. Maximum performance was recorded under 150 kg/ha nitrogen and phosphorous treatment and the decrease in phosphorous negatively affected plant performance. The results therefore suggest that yield and secondary metabolites increased with an increase in nitrogen and phosphorous treatment in the salt stressed madder.