the effect of irrigation regimes and mulch application on vegetative indices and essential oil content of peppermint (mentha piperita l.)

peppermint (mentha piperita l.) from lamiaceae family is one of the most important medicinal plants, used in food, sanitary and cosmetic industries. a field experiment was carried out in ferdowsi university of mashhad in 2010-2011 to evaluate the effects of three irrigation levels (100, 80 and 60 percent of water requirements calculated by evaporation pan class a) and two mulch types (black plastic and wood chips) in comparison to control (without mulch) on physiological parameter and essential oils content in a factorial experiments on the basis of randimised complete block desing with four replications. the data obtained from each harvest analyzed as a factorial experiment on the basis of randomized complete block design with four replications and the results of two harvests analyzed as split plot on time. the results of two harvest indicated that peppermint plants grow better in the first harvest than the second harvest. plants collected in the first harvest showed higher dry matter and essential oil yield. the highest dry herb yield (44.12 g/plant), the highest percentage of essential oil (2.835 %v/w) and the highest essential oil yield (116.7 l/ha) detected in plots treated with third level of irrigation and use of wood chips mulch. in conclusion the results also confirmed that the highest dry herb and the highest oil yield per area unit were observed in plots treated with third level of irrigation with use of wood chips mulch.