The effect of irrigation and nitrogen on the yield and composition of peppermint oil (Mentha piperita L.)

Abstract

Peppermint was harvested twice during the growing season. Harvest 1 was conducted on 16 February 1979, and the subsequent regrowth was harvested on 25 April 1979. High peppermint oil yields were associated with high rates of nitrogen fertilizer (100, 200 and 300 kg nitrogen/ha), and high levels of irrigation (50 mm per week) throughout the last half of the growing season. The composition of oil extracted from herb at the commercial harvest date was not significantly affected by either nitrogen or irrigation treatments. The oil yield from regrowth within the same growing season was significantly affected by irrigation and nitrogen treatments applied prior to the first harvest. When 300 kg nitrogen/ha and 50 mm of irrigation weekly (during the last half of the growing season) were applied, the oil yields from regrowth approached the commercial yield obtained from one harvest. Oil from regrowth contained high levels of menthol, menthyl acetate, menthofuran and limonene, and low levels of menthone and cineole. The possibility of obtaining two commercial harvests of peppermint per season, under southern Tasmanian conditions, is discussed