Foliar applications of phosphate increase the yield of essential oil in menthol mint (Mentha arvensis)

Field experiments were conducted at Lucknow, India, to study the effect of foliar application of orthophosphoric acid and diammonium phosphate filtrate on the biosynthesis and yield of essential oil in transplanted menthol mint: a foliage rich and vegetatively harvested crop. A foliar spray of 10% diammonium phosphate filtrate on the plants of menthol mint enhanced the biosynthesis of essential oil in the leaves to the extent of 15.6-18.7% over the control. A spray of 0.1% orthophosphoric acid gave an increase in the range 8.0-9.4%. When different varieties of menthol mint were sprayed with 10% diammonium phosphate filtrate, the variety Kosi exhibited 13, 78.3 and 66% higher essential oil yield over the varieties Himalaya, Hariti and Kalka, respectively. At the same concentration of spray, the variety Kosi enhanced the essential oil yield by 60% compared with that of the control. The early transplanted crop ( 18 March) was found to be good in terms of higher essential oil production by about 31% than the later transplanted crop ( 31 March). It is recommended that in order to get a high essential oil yield from a transplanted mint crop, a foliar spray of 10% diammonium phosphate filtrate should be applied twice, first in the second week of April and second in the first week of June. The optimum time to transplant mint plantlets in the field is the third week of March. A putative working metabolic model of the phosphate effect on biosynthesis of essential oil in volatile plants has been proposed.