RESPONSE OF MIDWESTERN PEPPERMINT (MENTHA X PIPERITA L.) AND NATIVE SPEARMINT (M. SPICATA L.) TO RATE AND FORM OF NITROGEN FERTILIZER
Peppermint (Mentha x piperita L. cv. 'Black Mitcham') and native Spearmint (M. spicata L.) were grown in northern Indiana (41.5°N latitude), and evaluated for their response to nitrogen rates and form (ammonium sulfate, calcium nitrate, urea and anhydrous ammonia). Plants were measured for total dry weight, total essential oil yield, total nitrogen content (in top 10 cm leaf/stem tissue), and leaf chlorophyll level. Rates and forms of nitrogen applied varied according to site and crop, with anhydrous NH3 treatments of 0, 45, 90, 135, 179, 224 kg/ha, and mineral fertilization rates of 0, 56, 112 and 168 kg/ha. In April, mineral fertilizers were broadcast by hand over the plots, or anhydrous ammonia was injected using a tractor-pulled injection rig. Two year (1993–1994) averages from plots comparing different forms of mineral fertilizers on peppermint showed increased essential oil yields from the 168 kg/ha rate over the 112 and 56 kg/ha nitrogen rates. Calcium nitrate gave the highest essential oil yields (2-year average) with 93.0 kg/ha, compared to urea (87.1 kg/ha) and ammonium sulfate (85.0 kg/ha). Anhydrous ammonia can be an effective source of nitrogen for peppermint and spearmint. At the highest anhydrous ammonia application rates, peppermint and spearmint were not damaged, with no apparent burning of roots or stolons. Peppermint essential oil yields were highest in 1993 using only the 45 kg anhydrous ammonia kg/ha nitrogen rate with calculated yields of 121 kg/ha. Oil yields were lower in plots with the highest nitrogen rates because of overgrowth and lodging. In 1994, highest yields came from nitrogen rates of 179 kg/ha, with calculated oil yields of 142 kg/ha. Leaf chlorophyll levels and leaf/stem nitrogen percent declined from May until harvest in July. Two year essential oil yield averages with native spearmint using anhydrous NH3 in a fall-plowed and non-fall plowed commercial field showed that rates of 168 kg/ha nitrogen consistently resulted in the highest oil yield, with 46.8 (fall plowed) and 57.9 kg/ha (nonfall plowed).
Alkire, Ben H. and Simon, James E. (1996). RESPONSE OF MIDWESTERN PEPPERMINT (MENTHA X PIPERITA L.) AND NATIVE SPEARMINT (M. SPICATA L.) TO RATE AND FORM OF NITROGEN FERTILIZER. Acta Hortic. 426, 537-550
mint, essential oil, anhydrous ammonia, yield