Effect of nitrogen fertilizer and salicylic acid spraying on growth and volatile oil content of peppermint (Mentha piperita L.)

A field study was carried out at the Agricultural Research Station of the Agriculture College, Al-Muthanna University (located in southern Iraq) , during season growth 2022.The study aims to know the effect of two factors, first one : adding nitrogen at three levels (0, 75 and 150 Kg. N. ha-1 ), second factor : spraying salicylic acid with three different concentrations (0, 100, 200 mg. SA. L-1 ) and their interaction on growth and essential oil yield of peppermint (Mentha piperita L.). Results showed the significantly superiority of nitrogen fertilizer level 150 Kg. N. ha-1 in all studied characteristics : plant height, branches number, leaves number, fresh weight of the shoot , dry weight of the shoot, volatile oil content and volatile oil yield (46.92cm, 16.89 branch plant-1 ,153.7 leaves plant-1 , 17.49 g plant, 2.66 g plant, 1.02% and 271.0 µL plant-1 , respectively. The peppermint plants sprayed with a concentration (200 mg SA. L-1 ) were significantly superior in plant height, branches number, leaves number, shoot fresh and shoot dry weight (42.88cm, 13.52 branch plant-1 ,129.9 leaf plant-1 , 12.97 g plant-1 and 1.98 g plant-1 ), respectively. While plants treated with concentration (100 mg. SA. L-1 ) gave the highest significant values of volatile oil content and yield of volatile oil ( 0.96 % , 291.9 µL plant), respectively. The interaction treatment (150 Kg. N. ha-1 , with 200 mg SA. L-1 ) gave the highest rates for all the studied except yield of essential oil was a highest in treatment (150 Kg. N. ha-1 , with 100 mg SA. L-1 )