Author(s): M. RAOOFI AND S. GITI

Abstract: The effect of hand weeding and different densities of planting was investigated on the yield, essential oil content and some morphological properties of peppermint (Mentha piperita L.) in which a factorial experiment was carried out based on a completely randomized block design with three replications in two harvest in Hamadan region and in two cropping seasons of 2012 and 2013. The experimental factors include weed control in two levels (hand weeding and non-hand weeding), and plant density on four levels (6, 10, 14 and 18 plants m^-2). The identified weeds in the field, include Sorgum halepense, Convolvulus arvensis, Avena ludoviciana, Solanum nigrum, Mallow, Plantago major and Chenopodium album L. The results of both harvests showed that the presence of weeds led to a qualitative and quantitative reduction of peppermint. Peppermint had more favorable growth in the first harvest than the second one, so that this plant provided the maximum essential oil yield and wet/dry yield in the first harvest. The hand weeding increased wet weight, dry weight, yield of the essential oil, leaf area and green cover percentage; the increased density had a significant effect on wet/dry weight gain, essential oil yield and green cover percentage, so that maximum yield of the mentioned items was obtained in densities of 18 plants m^-2. The results showed that the adequate density of plants is required due to increase the quantity and quality of peppermint as a medicinal plant.

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