Document Type : Research Article
Authors
1 Ferdowsi university
2 Department of Soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad
3 , Department of Soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad
Abstract
The effect of organic fertilizers application and humic acid foliar sprying on growth characteristics of stevia (Stevia rebaudiana Bertoni) in a saline soil
Abstract
Saline soils due to lack of organic matter and poor physicochemical properties and subsequent lack of moisture, usually having poor vegetation. The use of organic fertilizers in saline soils, can improve the growth and tolerance of plants under salinity conditions by improving the physical and chemical properties of the soil. For this purpose, this research was carried out with two types of organic fertilizers to modify saline soil properties along with humic acid foliar application as a stimulant for the growth of the Stevia plant. The experimental factors included the first factor: 1) control (without organic fertilizer), 2) vermi compost (20 ton/ha), 3) vermi compost (40 ton/ha), 4) Spent mushroom compost (20 tons/ha), 5) Spent mushroom compost (40 ton/ha), and the second factor was foliar spraying of humic acid at two levels of 0 and 0.1% in a Completely Randomized Design (factorial) with three replications. Photosynthesis rate, leaf area, plant dry weight, pH, salinity, bulk density and soil organic carbon were investigated in order to determine the most effective organic matter treatment under soil salinity stress conditions. Results showed that spent mushroom compost fertilizer (SMC) significantly decreased soil pH, bulk density, but increased electrical conductivity and soil organic carbon. Leaf area was reduced but total phenol, chlorophyll a, b, total and Carotenoid were increased resulting in significant increase in the dry weight of Stevia plants in saline soil. The highest dry weight of the plant was obtained with the application of 40 tons/ha of SMC fertilizer and humic acid foliar application, which was 45.12% more than the control (without fertilizer). Therefore, SMC fertilizer can be a suitable remediator for saline soil, humic acid spray also had a significant positive effect if used along with SMC soil application.
Key words: Stevia sweet leaf, plant biostimulants, humic acid, soil salinity
Materials and methods:
This experiment was conducted in a completely randomized design (factorial) in boxes (dimensions 30x40x30 cm) containing natural saline soil (EC=10.15 dS/m) under natural agronomic conditions in The Ferdowsi University of Mashhad with three replications from July to January 2018. Experimental factors were included the first factor: 1) control (without organic fertilizer), 2) vermicompost 20 tons/ha, 3) vermicompost 40 tons/ha, 4) Spent mushroom compost 20 tons/ha, 5) Spent mushroom compost 40 tons per hectare and the second factor: foliar spraying of humic acid at two levels of zero and 0.1%.
A soil sample was collected from Kushk region of Neyshabur city) with desired salinity (ECe=10.15 dS/m) and some physical and chemical properties of soil and organic fertilizers were measured before the experiment. Organic fertilizers after mixing with the experimental soil, were added to the plastic boxes according to the amount of each treatment. 2 seedlings were planted in each plastic box at a distance of 20 cm. Irrigation was done with tap water daily and one month after the adaptation of the stevia plant to the climatic conditions of Mashhad, humic acid foliar spraying was done in three stages with 20 days intervals.
After plant physiological stge some parameters including plant dry weight, leaf area, total plant phenol, amount of chlorophyll a, b, carotenoid, total plant chlorophyll, and soil organic carbon, bulk density, salinity, and soil pH , were determined after plant harvest. The dry weight of the stevia plant was obtained by weighing the plants after drying in an oven for 48 hours at 70°C. Statistical analysis of data was performed by JMP software version 0.8, drawing graphs using Excel software and comparing average data using LSD test at significance levels 1 and 5 percent.
Conclusion:
According to the results of this research, the application of SMC fertilizer with and without foliar application of humic acid was able to significantly increase the dry weight of the stevia plant compared to the control (without fertilizer) through modifying the physical and chemical properties of saline soil (pH, OC, bulk density) and some phytochemical properties of the plant (Photosynthetic pigments and total phenol). Application of VC fertilizer was not successful. Even though humic acid foliar application increased the total plant phenol, it could not improve the growth of the plant in saline soil alone, but it could increase the dry weight of the plant only with the application of SMC fertilizer. Thus, the highest dry weight of stevia plant was obtained with the application of 40 ton/ha of SMC fertilizer and humic acid spraying.Therefore, it is suggested that in order to achieve proper performance (≥80%) and improvement in the physiological and morphological characteristics of the stevia plant in very saline soil (ECe≥10 dS/m), it is necessary to use 40 tons/ha or more of mushroom compost waste. It should be used in saline soil three to six months before cultivation and 0.1% humic acid foliar spraying should be done three times with an interval of 20 days.
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