Effect of different fertilizer sources and harvesting time on the growth characteristics, nutrient uptakes, essential oil productivity and composition of Mentha x piperita L.

The excessive use of chemical fertilizers in conventional agricultural systems decreased the nutrient use efficiency and caused serious environmental problems such as waterway pollution, mineral depletion, soil acidification and other issues. In order to achieve the desirable essential oil productivity and reduction consumption of chemical inputs in peppermint (Mentha x piperita L.), a 2-year field experiment was carried out using a split-plot approach based on a randomized complete block design (RCBD), with 7 treatments and three replications at two harvesting times. The main factor was given by different fertilizer treatments including no fertilizer (control), chemical fertilizer, arbuscular mycorrhiza fungus, 50 % chemical fertilizer + arbuscular mycorrhiza fungus, nano chelated fertilizer, 50 % chemical fertilizer + nano chelated fertilizer, nano chelated fertilizer + arbuscular mycorrhiza fungus, and the sub-factor included two harvesting times (first harvest and second harvest). The results demonstrated that the highest and lowest growth parameters including plant height, number of lateral branches per plant and leaf greenness (SPAD index) were achieved with integrative application of 50 % chemical fertilizer + nano chelated fertilizer (in the first harvest) and control conditions (in the second harvest), respectively. Also, the maximum concentration of N, P, K and Fe was reached in the first harvest with application of 50 % chemical fertilizer + nano chelated fertilizer. Furthermore, the highest peppermint dry matter yield (354.8 g/m2), essential oil content (2.7 %) and essential oil yield (6.6 g/m2) was achieved at the first harvest with application of 50 % chemical fertilizer + nano chelated fertilizer. GC–MS analysis of peppermint essential oil showed that the major components at first harvest were menthol (31.82–37.87 %), menthone (23.85–30.90 %), 1,8-cineole (6.39–6.82 %), δ-terpineol (3.61–4.11 %) and neo-menthol (2.67–3.33 %), whereas at second harvest menthol (44–47.31 %), p-menth-l-en-9-ol (11.66–14.96 %), menthofuran (3.44–5.14 %), menthone (3.82–10.62 %), 1,8-cineole (5.51–5.99 %) and neo-menthol (5.03–5.90 %). Notably, menthol reached the highest amount with application of 50 % chemical fertilizer + nano chelated fertilizer. Overall, an integrative application of chemical fertilizers with nano fertilizers can be suggested to farmers as an alternative and environmentally friendly strategy to improve the quali-quantitative characteristics of peppermint essential oil.