Effects of Micronutrients and Humic Substance Application on some Quantitative and Qualitative Traits of Medicinal and Aromatic Herbs of Istanbul oregano

Introduction The Lamiaceae is a chief medicinal and aromatic plant family. It is a family of extensive diversity and variety with international distribution. It is known that most of their properties are due to the essential oils they contain as products of their secondary metabolism. The metabolic performance of living organisms can be distinguished into primary and secondary metabolisms. Secondary metabolites represent features that can be expressed in terms of ecological, taxonomic, and biochemical differentiation and diversity. The antioxidant properties of the volatile oils are not as robust as that of water-soluble constituents. Oregano, a member of the family is an herb that has been cultivated for centuries in the Mediterranean region, although now it can be found in most continents. Because of variability in composition and origin of different Origanum spp, the antioxidant capacity reported can vary substantially. In one study, oregano had the highest total antioxidant capacity and phenolic content compared with other Lamiaceae herbs, thyme, sage, rosemary, mint, and sweet basil. Istanbul oregano (Origanum vulgare ssp. hirtum (Link) Ietswaart)is a perennial plant with dense indumentum, white and pink flowers, strong fragrance, and flowering in July and August. It grows widelyin the Thrace, Marmara, and west and southern regions of Turkey. The plant is richer in oil and carvacrol content than O. onites and if improved, agronomic affairs would offer a better alternative. The environmental and social reasons indicate that conventional agriculture constitutes a continuous pressure contributing to the progressive worsening of environmental conditions. In this matter, the increasing use of saline irrigation water is one of the main factors resulting in salt accumulation in the plant rhizosphere. In this situation, soil degradation emphasized the need to develop strategies of salt affected soil reclamation. One of the possible solutions is to use humic substances. Micronutrients are essential elements that are used by plants in small quantities. Yield and quality of agricultural products increased with micronutrients application; therefore, human and animal health is protected with a feed of enrichment plant materials. Each essential element only can perform its role in plant nutrition properly when other necessary elements are available in balanced ratios for the plant. The aim of this trial was to study the effects of some micronutrients and humic substances on the antioxidant activity of the plant. Materials and Methods The trial was conducted at the experimental fields (37.53° N, 45.08° E, and 1320 m) and the greenhouse of the Agronomy Department, Faculty of Agriculture and the Lab of Biology Department, Urmia University, during 2015-2016, prepared in a randomized complete block design in three replications, using Fe, Zn, Cu, humic acid and their incorporation (3 g Lit-1) spray as treatments. The land was plowed at the optimum moisture level (field capacity) and leveled. Phosphorus and Potassium fertilizers were applied at pre-sowing time in autumn, according to soil analysis and farrowed in 50 cm. The seeds for sowing were obtained from Turkey. Sowing was done in green house at the Department of Horticulture, Faculty of Agriculture, Urmia University, during the period from 21. 03. 2015 till 06.05.2015. The seeds were sowed in plastic pots filled with soil, sand, and peat moss substrate as a material for germination. After that sowing was irrigated regularly depending on weather conditions and development stage of plants. Seedlings were harvested and planted in the experimental field. Nitrogen fertilizer was used in planting time, and vegetative phase according to soil analysis. Irrigation was conducted depending on plants need. Harvestings were done in 50% flowering. Physical and chemical characteristics of the field soil were determined by the standard method. Total phenolic content, flavonoid content, DPPH radical scavenging activity, nitric oxide radical scavenging activity, and Chain-breaking activitywere determined. Results The aim of this study was to increase the amount of oregano essential oil, and the use of micronutrients and humic substances increased the essential oil content of the plant. According to the results, the highest and lowest leaf dry weight was related to Zn+Cu+HA+Fe and Cu treatments, respectively. The highest essential oil content (3.50%) was recorded in Zn+Cu+HA and the lowest (2.28%) in Fe+HA treatments. The highest amount of total phenol in the plant leaves (72.7 g gallic acid/ 100 g DW) in Zn, flavonoid content (88.8 g quercetin/ 100 g DW) in HA and DPPH radical scavenging activity (74.1%) were observed in Fe+Cu+Zn+HA sprayings. In addition maximum nitric oxide radical scavenging (50.3%) and Chain-breaking activity (70.7 -Abs-3/min/mg extract) were observed in Zn and Fe+Zn treatments, respectively. In conclusion, the type of micronutrients and humic substances can affect the quality traits such as essential oil and antioxidant activity and according to the use target of the plant, combined and non-combined consumption of micronutrients, and humic substances can be recommended.