Nitrogen and Harvest Time Effect On Peppermint Biomass and Oil Yields In the Hot Humid Conditions of Mississippi.

Our previous studies conducted in 2007 and in 2008 demonstrated the agronomic feasibility of growing peppermint in Mississippi. Field experiments were continued in 2009 and in 2010 in Verona, Mississippi to evaluate N application rates (0, 80, 160, and 240 kg/ha) and harvest time (bud formation and flowering) on peppermint (Mentha X piperita) cv. Black Mitcham. The responses were measured repeatedly at two harvests (Cut 1 and Cut 2). The data were analyzed as repeated measures in a two-factor factorial design with eight blocks using combinations of the four blocks and the 2 yr as the blocks. Overall, fresh herbage yields were highest from the first cut at flowering stage, lower from the first cut at bud formation, and the lowest from the second cuts. N application increased herbage yields relative to the unfertilized control; N at 240 kg/ha provided greatest yields. Generally, the essential oil content, biomass, and oil yields from the first cut were greater than from the second cut. Greatest oil yields were obtained from the 240 kg/ha N treatment harvested in bud formation. This study further confirmed the feasibility of the establishment of peppermint as essential oil crop in Mississippi and possibly other areas of Southeastern US. However, in some years, peppermint oil produced in Mississippi had relatively low concentration of menthol compared to peppermint oil produced in Northwestern US, which may become a limiting factor for expanding peppermint production in the South. Further research is needed to identify agronomic means for ensuring high menthol concentration in peppermint oil produced in the Southeastern US.