Effect of date of planting and harvesting schedule on heat-unit accumulation and biomass production in Japanese mint (Mentha arvensis)

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The present investigation was carried out during the spring season of 2010 and 2011 at Ludhiana, Punjab, to study the effect of heat-unit accumulation on herb and oil productivity of Japanese mint (Mentha arvensis L.) under different dates of planting and harvesting schedules. The field experiment was laid out in split-plot design keeping 4 dates of planting 1 January, 15 January, 30 January and 15 February in main plots and 3 harvesting schedules (120, 135 and 150 days after planting) in subplots. Japanese mint planted on 15 February recorded the maximum fresh-herb and oil yields, which were statistically at par with that planted on 30 January, but were significantly higher than 15 January and 1 January plantings. The crop planted on 30 January and 15 February accumulated 456 and 624 and 222 and 390 units higher growing degree-days (GDD) than 1 January and 15 January planted crop respectively. The fresh-herb and oil yield of mint increased successively and significantly with delay in har- vesting from 120 to 150 days after planting (DAP). The growing degree-days (GDD), photothermal units (PTU) and heliothermal units (HTU) accumulation were 649, 8,866 and 5,275 and 322, 4,480 and 2,548 units higher in crop harvested at 150 DAP than that harvested 120 and 135 DAP respectively. The interaction effects revealed that crop planted on 15 February and harvested at 150 DAP gave the maximum biomass and oil yield, which were sta- tistically at par with that planted on 30 January and harvested at 150 days after planting, but was significantly bet- ter than all other combination because of higher accumulation of GDD, HTU and PTU. The multiple regression model was found to be well fit with P=0.0006, which revealed that fresh- herb yield of mint was significantly and positively correlated with GDD, HTU and PTU at multiple correlation value of 0.9636.