Planting Date and Straw Mulch Affect Biomass Yield, Oil Yield and Oil Quality of Japanese mint (Mentha arvensis L.) Harvested at Successive Intervals

In northwest India Japanese mint is being cultivated during spring season and faces both the extremes of temperature. The present investigation was planned to find out the optimum time of planting and harvesting with and without application of mulch to realize high quality essential oil. The experiment was laid out in split plot design keeping combinations of four date of planting (Jan 1, Jan 15, Jan 30 and Feb 15) and two straw mulch levels (No mulch and mulch @ 6 t/ha) in main plots and three harvesting schedules (120, 135 and 150 days after planting) in sub plots. Japanese mint planted on Feb 15 recorded maximum fresh herb, dry herb and oil yield, which were statistically at par with that planted on Jan 30 but were significantly higher than Jan 15 and Jan 1 plantings. Application of straw mulch resulted in significant improvement in fresh herb, dry herb and oil yield of Japanese mint. Fresh herb, dry herb and oil yield were significantly higher in crop harvested at 150 DAP than 135 and 120 DAP. Menthol content in mint oil did not influence with change in planting date or harvesting schedules while, menthone content decreased significantly with delay in harvesting from 120 to 150 DAP. A strong positive and linear relation was observed between emergence count and delay in planting of Japanese mint. Oil yield was positively correlated with plant height, stools count and fresh herbage production, while leaf to stem ratio has positive relation with oil content.