Effect of Nutrition and Harvest Time on Growth and Essential Oil Content of Thymus vulgaris L.

Thyme (Thymus vulgaris L.) is an important medicinal plant with highly valuable essential oils. In this study, effects of different fertilizer treatments and cuts on Thymus vulgaris L. was evaluated in 2008-2009. The research was conducted at Alborz Research Station, Research Institute of Forests and Rangelands, Karaj, Iran. The Experimental design was split plot in time in the form of a randomized complete block design with three replications. The main factor was nutrition in 16 levels consisting of different combinations of nitrogen (N), phosphorus (P), potassium (K) and manure (M): N0P0K0M0, N40P32K40M0, N80P64K80M0, N120P96K120M0, N160P128K160M0, N140P112K140M5, N120P96K120M10, N100P80K100M15, N80P64K80M20, N60P48K60M25, N40P32K40M30, N20P16K20M35, N0P0K0M40, N0P0K0M30, N0P0K0M20 and N0P0K0M10 (indices following the letters N, P and K are application rates in kg/ha, indices following the letter M are the application rates of manure in t/ha). The sub factor was harvest (cut) time (late May and early September). Results indicated that fertilizer, harvest date and their interactions significantly affected most of the traits. Mean comparison of the interactions indicated that treatments containing both chemical fertilizers and manure showed positive effects, although the most plant height was achieved with N160P128K160M0 × 1st cut, in both years (32.5 cm in 2008 and 32.66 cm in 2009). Essential oil yield was the highest in 2008 in N120P96K120M10 × 2nd cut (26.01 kg/ha), and in 2009 in N100P80K100M15 × 1st cut (26.79 kg/ha). Generally, it can be concluded from the results that T. vulgaris responds well to fertilization, and selecting the best treatment depends on the objective of production.