Effect of varying levels of nitrate on the growth and nitrogen metabolism of Japanese mint (Mentha arvensis L. Var. Pipemascens)

The plants of Japanese mint (Mentha arvensis L. var. piperascens Holmes) were grown in sand nutrient culture containing 0.0, 0.25, 0.50, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0 and 64.0 me/1 of NO₃^- in cemented pots. Less than 4 me/1 of NO₃^- reduced dry matter production. The growth was the maximum at 16 me/1 of NO₃^-, beyond which (32.0 and 64.0 me/1) it reduced considerably. Increasing levels of nitrate (0.0-64.0 me/1) increased ammoniacal, amide, nitrate and ‘rest’ nitrogen, while the contents of insoluble - N showed a progressive increase only up to 16 me/1 of NO₃^-, and a decrease thereafter.