Effect of the mineral fertilization on the yield and the oil content of two cultivars of rosemary

In the years 2001-2003 two cultivars of rosemary (“Majorka pink” and “Montfort form”) were grown in peat and perlite (4:1 v/v) into plastic pots with a diameter of 22 cm. We tested the combined application of three doses of N (0–100–200 mg/plant), three of P2O5 (0–40–80 mg/plant) and three of K2O (0–100–200 mg/plant), each applied every 20 days (25 applications during the entire cycle). For each cultivar we realized a completely randomized experimental design with eight replications. Two harvests, respectively when plants were one and two years old, were done. In both the cultivars and harvests, N, P and K enhanced yield, but only N had a significant effect on the height and the diameter of the plants. The best fertilizer combination was 200 N, 40 P2O5 and 200 K2O mg/plant. N, P2O5 and K2O uptakes were respectively 10.4 g, 4.04 g and 13 g per kg of dry matter, being N:P2O5:K2O = 2.5:1:3.2. Oil content and composition were different in the two cultivars: “Majorka pink” had the highest oil content and was particularly rich in camphor; “Montfort form” in alpha-pinene, borneol and 1,8-cineole. Fertilization had different effects on the oil composition of the two cultivars, particularly on the percentage occurrence of borneol and oxygenated compounds. N and K always reduced camphor content, whereas P reduced it in “Majorka pink” and enhanced it in “Montfort form”. Furthermore, N and K increased alpha-pinene, whereas P enhanced it only in “Majorka pink”. In both the cultivars, N enhanced linalool, camphene and myrcene, P enhanced limonene, K enhanced p-cymene and reduced 1,8-cineole. The essential oil production per kg of fresh weight was not affected by fertilization. In “Majorka pink” the fertilization with N, P and K increased the number of capitate glandular trichomes in comparison with the control. Non-glandular hairs were scattered in “Majorka pink”, whereas they formed a dense covering in “Montfort form”, obscuring the epidermal surface.