The results relating to the influence of the increasing doses of nitrogen (0-200 kg/ha), with constant amounts of phosphorus (80 kg/ha) and potassium (50 kg/ha), on the yield and quality of peppermint (Mentha piperita L.) are presented in this paper.
These researches are carried out in 1998/99 by field trial on 35 m2 parcels, with five fertilizer treatments in four replications. The trial was conducted on the humoglay soil type at the Experimental field station of the Institute for medicinal plant research in Pančevo. The usual agrotechnique was applied during the spring 1999. The harvest of peppermint was done twice, in June and September (I and II).
The significant differences were obtained for the peppermint yield between the fertilizer treatments. The yields of dried peppermint's herb and leaves mostly increased with the nitrogen fertilizer dose and ranged from 1650 to 6820 kg/ha (for dried herb). Beside that, it was noticed that the use of different fertilizer amounts had influence on the content of the peppermint's dry matter. The differences regarding peppermint's leave/stem ratio were also noticed. The variability of N, P, K contents in the peppermint was not expressed, which points out greater influence of genetic features of this species.
The essential oil content in the peppermint also varied less under the influence of different fertilizer doses, and was greatly depended on the time of harvest. It ranged from 1.65 to 2.05 %, while the highest amount was obtained in the third phase of the first harvest. Since the peppermint yields were higher when higher nitrogen fertilizer doses were applied, the total essential oil yield per one hectare was simultaneously higher.
Key words: peppermint, mineral fertilizers, herb yield, essential oil, essential elements.