Nitrogen and Sulfur with Thiobacillus Bacteria Effects on Garlic Yield and Garlic Nitrate Content and some Nutrients Availability in Soil

Introduction: Garlic (Allium sativum L) is the second most commonly used herb of alliums after onions. This plant has significant effects on lowering blood pressure, preventing atherosclerosis, reducing blood cholesterol and triglyceride and inhibiting platelet aggregation. In recent years, the increase in the yield of this product has been of interest to manufacturers of this product with respect to the preservation of qualitative characteristics, including the maximum content of nitrate. It has been shown that the absorption of nutrients in the soil affects the yield and yield components of the plant. In this regard, the timely and adequate supply of nutrients such as sulfur and nitrogen has a special role in promoting quantitative and qualitative characteristics of garlic. Material and Methods: In order to study the effects of nitrogen and sulfur consumption on quantitative and qualitative traits of garlic, this study was conducted with 12 treatments and three replications in the form of a split plot design in two years in Agricultural Research Center of Agricultural and Natural Resources of Tehran Province which located in Varamin in Iran. Nitrogen factor was considered at four levels (0, 100, 200 and 300 kg ha-1) and sulfur at three levels (0, 500 and 1000 kg ha-1 with inoculation of Thiobacillus). Before planting, soil samples were taken from the experimental site and physical and chemical characteristics including texture, reaction, organic carbon, lime, nitrogen, phosphorus and potassium, and iron, manganese, copper, zinc and boron were measured. Dry matter yield, number of bulbs per garlic, single plant weight, garlic weight, plant height, leaf number per plant and leaf area were recorded at the end of experiment. Garlic nitrate content and nutrient concentration in garlic leaves were also measured. Data obtained were analyzed statistically using SAS software. Results and Discussion: The effects of nitrogen and sulfur on the yield of garlic cloves, number of bulbs in cloves, cloves weights, bulbs weights, plant height, leaf area and bulb nitrate were significant as all these traits were improved. Application of 1000 kg.ha-1 of sulfur increased the garlic cloves yield by 31% compared to the control. Nitrogen consumption up to 200 kg.ha-1 increased garlic cloves yield by 58% compared to the control. The highest economic yield of garlic cloves was obtained by 1000 kg.ha-1 sulfur and 200 kg.ha-1 nitrogen, which was 104% more than control treatment. Data also showed that the effects of sulfur and nitrogen and the interaction of sulfur and nitrogen on the leaf area of the garlic plant were significant. Consumption of 1000 kg.ha-1of sulfur increased the leaf area of the garlic plant by 42% compared to the control. Nitrogen consumption up to 200 kg.ha-1 increased the leaf area of garlic plant by 39.3% compared to the control. The highest leaf area of garlic plant was obtained from 1000 kg.ha-1sulfur and 200 kg.ha-1nitrogen, which was 104% higher than control. Increase of the growth and yield of garlic was attributed to the main role of nitrogen in increasing meristematic activity, cell division, prolongation of the cell. Sulfur is one of the essential nutrients of the plant, and without sulfur, the plant does not grow and function properly. Sulfur is the fourth essential element after nitrogen, potassium and phosphorus for garlic. This element is needed in production of amine acids, such as methionine and cysteine, which are essential for the production of vitamin A, and the activation of certain enzymes. The results of studies have shown that amino acids directly or indirectly affect the physiological activity of the plant, and positively affect the growth, increase in yield and increase plant tolerance to environmental stresses. The soil reaction was affected by sulfur consumption and decreased. There was a negative correlation between soil reaction as a dependent variable (Y) and consumed sulfur as an independent variable (X), which correlated with linear relation with correlation coefficient of 0.98. Data showed that use of 1000 kg.ha-1of sulfur reduced soil reaction from 7.49 to 7.26 and increased leaf iron concentration by 88% compared to control and increased leaf zinc concentration 110% compared to control treatment. The researchers believe that sulfur oxidation and sulfuric acid production in the soil reduce soil reactions and increase the absorption capacity of phosphorus and microelements. The effect of sulfur on the concentration of leaf phosphorus was significant. The phosphorus concentration was increased significantly with sulfur application into the soil, so that 1,000 kg.ha-1 of sulfur increased the concentration of leaf phosphorus by 63% compared with the control (0.33%). Research results have shown that phosphorus absorption capacity in soil is highly dependent on soil reaction and reducing soil reaction leads to increased phosphorus absorption capacity. Researchers have reported that sulfur consumption and the production of sulfuric acid, as a result of its oxidation, reduce soil reaction and increase phosphorus availability for plants. The effect of nitrogen, sulfur and the interaction of nitrogen and sulfur on the content of garlic nitrate was significant. Garlic nitrate content decreased with application of sulfur and increased with nitrogen addition. Application of sulfur at 1000 kg.ha-1 significantly reduced garlic nitrate content by 35% compared to control. The application of 100, 200 and 300 kg.ha-1 of nitrogen increased the content of garlic nitrate 97, 210 and 308%, respectively in comparison to control. At all levels of nitrogen addition, sulfur consumption reduced the content of garlic nitrate. Garlic nitrate content decreased with application of sulfur and increased with nitrogen addition.  Sulfur application at 1000 mg.kg-1 significantly reduced garlic nitrate content by 35% compared to control (mg.kg-1). Garlic nitrate was increased by the amount of nitrogen consumed. There was a positive correlation between garlic nitrate (Y) as a dependent variable (N) and independent nitrogen (X), which correlated with linear relation with the correlation coefficient of 0.99. Researchers have argued that excessive consumption of nitrogen fertilizers is the main factor causing the accumulation of nitrate in a number of vegetables and other plants such as garlic. Conclusion: Based on the results of the experiment, it was concluded that nitrogen and sulfur increase the yield of garlic. Meanwhile, sulfur reduces nitrate accumulation in garlic. Sulfur consumption reduces soil pH and increases the absorption availability of micronutrients and phosphorus in the soil and causes more absorption of these elements by the plant.