EFFECT OF INCREASING DOSES OF FERTILIZER APPLICATION ON QUANTITATIVE AND QUALITATIVE CHARACTERS OF MINT

In field experiments, we have studied the vegetative behaviour and productivity of Mentha, fertilized with three levels of fertilizers previously calculated to give varying yields of essential oil. Cultivar Tundza, cv. Zephir and clone No. 1 of Mentha piperita Huds and cv. Mentolna 18 of Mentha arvensis L. var piperascens were used as a test material. The levels of fertilizer application was the following: B0 - without fertilizers, B1 - N 151 kg/ha, B2 - N 306.2 kg/ha and K₂O 110 kg/ha, B3 - N 533.6 kg/ha, P₂O₅ 182 kg/ha and K₂O 240 kg/ha.

It was established that plant height, branching, and essential oil content were increased with increasing fertilizer rates. However, plant leafiness was not significantly affected by the increase of fertilizer rates.

With the increased fertilizer rates, the fresh herbage yield from the first harvest increased by 13 to 72%, and that from the second harvest - by 23 to 78% compared to the control. Cultivars Zephir and Tundza proved to be more productive than clone No. 1 and cv. Mentolna-18. No normal second harvest could be produced by cv. Mentolna-18.

With the increased fertilizer rates, the essential oil yield from the different cultivars increased by 16 to 119% compared to the control (BO). Cvs Zephir and Tundza were more productive and susceptible to fertilization and clone No 1 and Mentolna-18 were less productive and responsive to the increased fertilizer levels.

The level of fertilization did not affect significantly the content of main chemical compounds in the oils from the first swath, while in the essential oil obtained from the second swath the menthol content was increased.