Effect of Plant Growth Promoting Rhizobacteria on Yield and Yield Components of Garlic Medicinal Plant (Allium sativum L.) under the Conditions of Different Organic and Chemical Fertilizers Application

In recent years, the effect of exogenous organic amendments on soil properties and plant growth characteristics has received renewed attention. Although the utilization of mineral fertilizers could be viewed as the best solution in terms of plant productivity, this approach is often inefficient in long-term in tropical ecosystems due to the limited ability of low-activity clay soils to retain nutrients. Intensive use of agrochemicals in agricultural systems is also known to have irreversible effects on soil and water resources. Vermicompost is currently being promoted to improve soil quality, reduce water and fertilizer needs and therefore increase the sustainability of agricultural practices in tropical countries. Vermicomposting is a process which stabilizes organic matter under aerobic and mesophilic conditions through the joint action of earthworms and microorganisms. The products of vermicomposting have been successfully used to suppress plant pests and diseases, as well as increase crop productivity. Cow manure is an excellent fertilizer containing nitrogen, phosphorus, potassium and other nutrients. It also adds organic matter to the soil which may improve soil structure, aeration, soil moisture-holding capacity, and water infiltration. Biofertilizers are defined as preparations containing living cells or latent cells of efficient strains of microorganisms that help plant's nutrients uptake by their interactions in the rhizosphere when applied through seed or soil. They accelerate certain microbial processes in soil which augment the extent of availability of nutrients in a form easily assimilated by plants. Very often microorganisms are not as efficient in natural surroundings as one would expect them to be and therefore artificially multiplied cultures of efficient selected microorganisms play a vital role in accelerating the microbial processes in soil. Garlic (Allium sativum L.) is a very powerful medicinal plant that is often underestimated. Garlic is easy to grow and can be grown year-round in mild climates. Garlic cloves are used for consumption (raw and cooked) or for medicinal purposes. They have a pungent characteristic, spicy flavor that mellows and sweetens considerably with cooking.
In order to evaluate the effect of biofertilizers and organic and chemical fertilizers on yield and yield components of garlic (Allium sativum L.), a split plot experiment based on RCBD with three replications was conducted in 2015-2016 growing seasons, in Gonabad University, Iran. Main plot included different organic and chemical fertilizers (1- vermicompost, 2- cow manure, 3- chemical fertilizer and 4- control) and sub plot included plant growth promoting rhizobacteria (nitroxin, biophosphorous and control). In order to determine physic-chemical properties of soil, sampling was performed at the depth of 0 to 30 cm. Before cultivation, 7 and 30 t.ha-1 vermicompost and cow manure were added to the soil, respectively. Nutrient requirement of garlic for nitrogen, phosphorous and potassium from the chemical source was considered 40, 50 and 60 kg.ha-1. For application of biofertilizers, bulblets inoculated with plant growth promoting rhizobacteria for 15 minutes. Distance in and between rows was considered 10 and 20 cm, respectively. Weeds were controlled manually three times. At the end of the growing season, economic yield, biological yield, plant height, shoot dry weight, bulb diameter, bulblet weight per plant, bulblet volume per plant and bulblet number per plant were measured. Analysis of data variance was performed by using SAS software (Ver 9.1).
The results showed that simple effect of chemical fertilizer on bulb diameter was not significant but combined application of chemical fertilizer and biophosphorous increased bulb diameter as much as 18% compared to control. Combined application of nitroxin and cow manure increased bulblet weight per plant by 41% compared to single application of nitroxin. Biophosphorous plus vermicompost, cow manure and chemical fertilizer increased biological yield, respectively, by 25, 18 and 15% compared to single application of these fertilizers. The highest economic yield obtained in treatment of nitroxin plus cow manure. Organic and biological fertilizers are among the most significant resources for improvement of agricultural soil quality and increase in the yield of different medicinal plants. It has been reported that these ecological inputs provide favorable conditions for plant growth and development through improvement of physical, chemical and biological properties of the soil (10, 39), therefore, it can be concluded that improvement in most studied traits in the present study was due to the use of organic fertilizers. Fallahi et al. (22) reported the positive effects of organic and biological fertilizers on the improvement of quantitative and qualitative characteristics in chamomile (Matricaria chamomilla L.).
In general, the results of this research showed that combined use of organic and biological inputs can improve quantitative characteristics of plant, and thus decrease the environmental risks of chemical inpus.