he Effect of Water Stress, Chemical and Organic Fertilizers on Biomass, Seed Yield and Root Phenolic Compounds of Purple Coneflower(Echinacea purpurea L.)

Nowadays the demand for medicinal plants is increasing in the pharmaceutical industries. Echinacea spp. is an herbaceous, perennial plant containing valuable substances which belong to different chemical groups, most notably phenolic compounds. Echinacea is the most well-known and most important treatment for the immune system and protects against cough, cold and fever. Drought stress can be a major factor in increasing the content of secondary metabolites in many medicinal plants. Organic fertilizers are known to be one of the fertility factors for soil and plant nutrition due to the impacts on the physical, chemical and biological properties of soil. The purpose of this study was to investigate the response of yield and phenolic compounds as the most important group of active compounds in Echinacea in response to different levels of water stress, chemical and organic fertilizer management and their interactions.

This experiment was carried out during 2016 and 2017 years at the experimental Field of Ferdowsi University of Mashhad, located at 10 km East of Mashhad. The split plot based on factorial design was implemented in 3 Replications. The  studied factors in this experiment in the main plot were water stress at three levels, including1- Non-Water stress (6000 m3.ha-1), 2- Moderate Water Stress (4500 m3.ha-1), 3- Severe Water stress (3000 m3.ha-1).In sub plots, fertilization treatments applied in eight levels, including, 1- NPK fertilizer (500 kg.ha-1) ; 2-Humic acid (20 L.ha-1); 3-Vermicompost (6000 kg.ha-1); 4-Humic acid+NPK (20 L.ha-1+500 kg.ha-1); 5. Vermicompost+NPK (3000 kg.ha-1+250 kg.ha-1); 6-vermicompost+humic acid (3000 kg.ha-1+20 L.ha-1); 7. Vermicompost+Humic acid+NPK (3000 kg.ha-1+20 L.ha-1+250 kg.ha-1) and 8.control. The amount of irrigation needed at each turn was calculated by NETWAT software. In combined treatments, half of the NPK fertilizer which used in the pure treatment was replaced with the equivalent amount of vermicompost. Constant amount of liquid humic acid was applied at the same time with vermicompost and NPK in rosette leave developing and before stem-elongation phase. The total amount of phenolic compounds in the sample was evaluated by the Folin-Ciocalteu method. Data were analyzed with MSTAT-C statistic software and means compared by Duncan Multiple Range Test.

The most amounts of stem dry matter, flower dry matter and biomass were observed at vermicompost and non-stress treatment and the least amount of them was obtained from control and severe water stress condition. The highest amounts of leaf and root dry weight were obtained under vermicompost+humic acid and moderate water stress treatments and the least amount of leaf dry weight was observed at control and severe water stress treatments. At the same time with the increase of water stress, the impact of organic fertilizers on leaf dry weight decreased, however the application of organic fertilizers increased the leaf dry weight even under severe stress conditions. Maximum seed yield was observed under vermicompost+humic acid+NPK and NPK treatments with severe water stress condition. With increase in the stress level, root to shoot ratio was increased and the maximum amount of that was obtained in control treatment under severe water stress condition and the minimum amount of that was obtained at vermicompost and non-stress treatment. The application of vermicompost and humic acid increased root to shoot ratio in severe stress conditions and it were effective in developing root systems in these conditions. Maximum amounts of phenolic compounds were observed under humic acid+vermicompost treatment with severe stress condition and minimum of these compounds were obtained under humic acid treatment at no-stress. 

The response of aerial parts of plant was associated with a decrease in irrigation levels, however this trend was reversed in underground sections. Thus, the maximum amount of root dry weight, root to shoot ratio and root phenolic compounds were observed in severe stress treatment. The highest amount of Phenolic compounds of the root, the ultimate goal of this plant, were observed under humic acid+vermicompost combination treatments. Therefore the production of this plant in terms of supplying 50% of the required moisture content (is equivalent to 300 mm of irrigation during the one-year growth period) and the use of fertilizer treatments containing humic acid and vermicompost compounds is recommended.