Effects of Organic Fertilizers on Essential Oil Composition and Yield in Sustainable Cultivation of Hyssop (Hyssopus officinalis L.)

Organic fertilizers such as compost and vermicompost improve soil's physical and chemical properties that enhance beneficial microbe's activity in soil and nutrient availability by plants. Nitrogen-fixing bacteria such as Azotobacter and Azospirillum as biofertilizers also have the ability of nitrogen-fixing and release phytohormones which could stimulate plant growth, absorption of nutrients, and the photosynthesis process. Production of medicinal plants with using from biofertilizers leads to an increase of the quantity and quality of active substances such as essential oil. Hyssop (Hyssopus officinalis L.) is a perennial herb that grows wild and is cultivated in temperate regions of Asia, Europe, and America. The essential oil of hyssop is widely used as a traditional drug in some the parts of Asia and Europe to treat respiratory diseases. Hyssop is also used in food, pharmaceutical, flavor, and cosmetic industries throughout the world. The main constituents of hyssop essential oil have been reported as pinocamphone, pinocarvone, and phellandrene. 

In order to study the effects of compost, vermicompost, and nitrogen-fixing bacteria as sustainable nutrient management on the essential oil composition of Hyssopus officinalis, an experiment was conducted based on a randomized complete block design with eight treatments and three replications at the research field of Agriculture Company of Ran in Firouzkooh of Iran during 2012. The treatments were 20 t.ha-1 compost, 12 t.ha-1 vermicompost, biofertilizer (inoculated seeds with Azotobacter chroococcum and Azospirillum lipoferum), 10 t.ha-1 compost  + 6 t.ha-1 vermicompost,  20 t.ha-1 compost + biofertilizer, 12 t.ha-1 vermicompost  + biofertilizer, 10 t.ha-1 compost + 6 t.ha-1 vermicompost + biofertilizer and control (without fertilizer). Studied traits were contained herb yield and percent, yield, and composition of essential oil. The essential oil extraction was done by the hydro-distillation method in Clevenger’s apparatus, and essential oil composition was determined by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). Analysis of variance was conducted by SAS software, and the means were compared by the least significant difference test (LSD) at the 5% probability level.

Results showed that the highest herb yield (2601.6 kg.ha-1), essential oil percent (0.20%), and essential oil yield (5.21 kg.ha-1) were obtained in integrated application of 12 t.ha-1 vermicomposts and biofertilizer (nitrogen-fixing bacteria)(2 lit/ha). The maximum cis Pinocamphone percent (63.56%) and beta Phellandrene percentage (9.71%) and the minimum trans Pinocamphone percent (2.50%) in an essential oil by integrated using of 10 t.ha-1 compost, six t.ha-1 vermicomposts, and biofertilizer and the highest Valerianol percentage (5.36%) and Phytol percentage (2.19%) in essential oil with the application of  20 t.ha-1 compost were obtained.   Integrated application of vermicompost and biofertilizer through the high ability for absorption of mineral nutrients like N, P, and K by plants and then increase of biomass amount has a positive effect on essential oil content. Increased essential oil yield in treatment of the integrated application of vermicompost (12 t.ha-1) and biofertilizer can be owing to the improvement of yield attributes such as; essential oil percentage and herb yield. Some studies have reported that the application of bio and organic fertilizers can increase the content and yield of essential oil in a few medicinal plants such as basil, chamomile, and coriander. Integrated application of bio and organic fertilizers through the improvement of biological activities of soil and nutrient elements absorption such as nitrogen and phosphorus, caused more growth and biomass production, which leads to improvement of the essential oil quality. Several studies have shown a beneficial effect on the essential oil composition of medicinal plants by the integrated application of bio and organic fertilizers.  

Generally, the highest essential oil quantity with the integrated application of 12 t.ha-1 vermicomposts and biofertilizer and the highest essential oil quality with the integrated application of 10 t.ha-1 compost, six t.ha-1 vermicomposts and biofertilizer were obtained.