effects of sowing time and plant density on yield and essential oil production of medicinal plant, peppermint (mentha piperita l.)

in order to investigate the effects of two sowing time (middle of may and early june) and four plant density (8, 12, 16 and 20 plants.m-2) on yield and essential oil content of peppermint at two cutting stages, an experiment was conducted at the research farm of the faculty of agriculture, university of tabriz during growing season of 2003-2004. these treatments were performed as factorial based of randomized complete block design with three replications. the result of the first cutting showed that plant sowing at the early june and eight plants.m-2densities had the highest leaf (4.47%) and plant (2.92%) essential oil percentage, but these factors and their interaction effects did not effect on the essential oil yield. in the second cutting, the highest plant essential oil was observed in plant sowing at early june and 12 plants/m2 densities. the highest essential oil yield in second cutting produced in middle of may sowing time. the results of two cutting stages showed that the fresh and dry yield decreased by delaying in sowing time.