Effect of chemical, organic and biological fertilizers on growth and physiological characteristics of garlic (Allium sativum L.) in Guilan province

Garlic (Allium sativum L.) is one of the main vegetable crops grown in Iran. Garlic occupies a prominent position among human foods, not only as a condiment, but also due to its therapeutic properties, attributed to the presence of bioactive compounds (25). Garlic yield are varied with agricultural practices and cultivar. Application of the required nutrients through chemical fertilizers alone can have deleterious effect on soil health and can lead to unsustainable yields, while integration of chemical fertilizers with organic manures and biofertilizers can maintain soil health and soil productivity (3). Numerous bacteria are beneficial for plant productivity. Free-living soil bacteria such as Pseudomonas, Azotobacter and Azospirillum spp could add nutrients through the natural processes of nitrogen fixation, solubilizing phosphorus, and stimulating plant growth through the synthesis of growth-promoting substances (20 and 26). Hence, this experiment carried out in order to evaluate the effect of chemical, organic and bio-fertilizers on yield and some physiological characteristics of landrace garlic in Guilan climatic condition. This experiment was performed in 2016-2017 cropping season as split plot based on complete block design with three replications in Rasht, Iran. Three nitrogen sources including vermicompost (15 ton/ha), urea (100 kg N/ha), integrated management nutrient (7.5 ton/ha + 50 kg N/ha) and 10 biological inoculations including without inoculation as control, Azospirillum brasilense, Azospirillum lipoferum, Pseudomonas putida, Pseudomonas fluorescens, Azotobacter, Azospirillum + Pseudomonas, Azospirillum + Azotobacter, Pseudomonas + Azotobacter, Azospirillum + Pseudomonas + Azotobacter comprised experimental treatments. Results showed that the maximum plant height, leaf numbers, biological weight per plant and bulb yield were obtained under the application of chemical nitrogen fertilizer along with Pseudomonas + Azospirillum spp bacteria. Also, there was a positive and significant correlation between bulb yield and some characteristic such as plant height, leaf numbers and biological weight per plant. In addition, the simultaneous application of Azospirillum and Azotobacter biological fertilizers under using vermicompost caused to enhance bulb yield. In this experiment, simultaneous usage of all studied bio-fertilizers enhanced bulb yield under integrated nutrition system. In general, bulb yield and its attributes showed difference responses to the application of chemical, organic and bio-fertilizers. Based on results of this experiment, different biological fertilizers could be beneficial related to type of nutrition systems for bulb yield enhancement. In addition, the application of Azospirillum + Pseudomonas could be recommendable to improve biological and bulb yield of garlic in conventional agriculture and under region climatic condition.