Effect of Different levels of Seaweed Fertilizer on Growth Parameters, Yield and Essential Oil Content of Summer Savory (Satureja hortensis L.)

Introduction: Organic production is one of the important aspects in the medicinal plants industry and the use of organic fertilizers is very important in this topic. Seaweeds are important marine living resources with tremendous commercial applications and many commercial products from seaweed extract are used in agriculture and horticulture. Seaweed extracts can be used in liquid form as a foliar spray, soil drench or in powder and granular forms as soil conditioners and manure. Using seaweed extracts as fertilizers can improve plant productivity, because they contain growth-promoting hormones. Several studies have also shown that the seaweed extracts can suppress plant diseases and insect pests. Nowadays, seaweed extract is used as an organic fertilizer in order to increase the quantitative yield of medicinal plants and also resistance to environmental stresses. Summer savory is one of the medicinal and spice plants that has a high area under cultivation in our country for food and medicine. Various studies on its essential oil had been shown that it contains high amounts of phenolic compounds like Carvacrol, γ-Terpinene, Thymol, p-Cymene, β-Caryophyllene, Linalool, and other terpenoids. Materials and Methods: In order to study the effect of different levels of seaweed fertilizer on the growth characteristics, plant material yield, essential oil percentage of summer savory, an experiment was conducted as a randomized complete block design with 3 replications at the Faculty of Agriculture, Tarbiat Modares University (TMU) during 2017. The treatments included: 0 (control), 2.5, 5 and 10 ml/liter seaweed fertilizer that they were used as a foliar application for three times in the growing season. According to the meteorological data, the area had an average rainfall of 246 mm and a semi-arid climate. In order to determine the physical and chemical properties of the soil, soil sampling and testing were done. To prepare the field, the soil tillage operation was carried out using a 40 cm depth plow. Then, plots with a 2 × 2 meters at a distance of half a meter from each other were prepared. The seeds used in this experiment were prepared from Varamin landrace, which is mainly cultivated by farmers in Tehran and Alborz provinces. Sowing operation was carried out manually. In each plot, 7 rows (30 cm spacing between rows) were cultivated and all of the plots were irrigated in the same conditions. The organic fertilizer (Bioalgax) used in this experiment was based on an extract of seaweed (Ascophyllum nodosum), which was obtained from the Kimitec company, Spain. This fertilizer is a natural source of phytohormones such as cytokinins, auxins, and gibberellins and also, it has some minerals. After reaching the height of 20 cm (eight weeks after planting), spraying of the fertilizer solutions was applied three times during the growing season at intervals of 10 days. The foliar application was carried out at sunset time by using a manual sprayer. The harvest was carried out at full flowering stage and 3 plants of each plot were harvested. The studied traits were: plant height, stem diameter, the number of branches, leaf length, and width, shoot fresh and dry weight, root fresh and dry weight, SPAD index, essential oil yield and content.  Results and Discussion: The results showed that different concentrations of seaweed fertilizer had a significant effect on the number of branches, shoot dry weight, root fresh and dry weight, leaf width and plant height at 1% probability level. They also had a significant effect on the shoot fresh weight, essential oil percentage, and yield at 5% probability level. On the basis of the results, the highest number of branches (35.44), leaf length and width (43.22 and 8.07 mm), stem diameter (5.00 mm), root fresh and dry weight (15.17 and 6.42 g), shoot fresh and dry weight (181.01 and 37.69 g) and SPAD index (48.13) were obtained from 10 ml/liter seaweed fertilizer and the lowest amounts were observed in control treatment. The maximum plant height (54.66 cm) and the highest percentages and the yield of essential oil (2.51% and 6.28 g/m2) were also obtained from 5 ml/liter seaweed fertilizer. According to the results, the response of summer savory to the use of seaweed fertilizer was positive and it could be placed in the fertilization program of farmers.