St. Jonh's wort is a medicinal plant used for anti-depressive treatment. Hypericin is considered one of the compounds that contribute to the medicinal effect of the plant. Since the concentration and the total quantity of active ingredients may be affected by plant nutrition, this work was conducted to investigate the effects of soil pH and phosphorus (P) addition to the soil on initial growth and hypericin production of St. John's wort. The experiment was carried out in Lages, SC, from July until December of 2003, in a greenhouse. It followed a completely randomized factorial design (4 x 3), with four levels of pH (4.1, 5.5, 6.0, and 6.5) and three doses of P (0, 50, and 100 mg kg-1 of soil), and four replicates. Two plants were cultivated per pot, under a Humic Inceptisol. Plants were harvested and assessed for aerial dry matter production, height, number of lateral shoots, number of dark glands in the leaves, aerial hypericin content and aerial total hypericin production. The aerial dry matter production increased with P addition and, in a larger amount, with liming. The plant height was only affected by the liming. The number of lateral shoots and dark glands in the leaves as well as the hipericin concentration only increased with P application in the soil without liming, and with liming in the soil that did not receive P. The highest total hypericin production per pot was achieved in the treatments with pH values of 6.0 and 6.5 and P doses of 50 and 100 mg kg-1 of soil.
Hypericum perforatum L.; medicinal plants; phytoterapic; nutrition
