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General Concepts

Introduction

In recent decades, efforts to increase rice production and excessive and unbalanced use of chemical fertilizers had negative environmental consequences and increased production costs, necessitating a revision of new methods of increasing crop production. In this regard, the use of biofertilizers, one of the most important strategies for sustainable management of ecosystems and increasing production in sustainable agricultural systems. Biofertilizers are bacterial and fungal microorganisms that affect the growth and development of crops and soil properties by biologically nitrogen fixation, dissolving soil phosphorus and producing significant amounts of growth-promoting hormones (mainly oxins, gibberellins and cytokines).

Challenges and necessity

The use of growth-promoting bacteria (PGPRs) in crop production, while maintaining and improving the physical and chemical properties of the soil, reduce the consumption of chemical inputs, protect water and soil resources from pollution, increase crop yield, produce healthy-organic rice leading to sustainability in rice production. Use the technique of inoculation of rice plant’s roots or grains with plant growth promoting bacteria is a way to follow the correct principles of sustainable agriculture that can pave the way for the design and implementation of many research projects aimed at modulating and reducing the use of chemical fertilizers.

Research hypotheses

  1. Do the inoculation with non-symbiotic bacteria strains cause significant changes in rice yield and yield components?
  2. Do the inoculation with non-symbiotic bacteria strains cause significant changes in physical and chemical properties of paddy soil ?
  3. Do the inoculation with non-symbiotic bacteria strains cause significant changes in concentration of nutrition elements in grain and rice straw?
  4. Do the interaction of non-symbiotic bacteria and rice varieties cause significant changes in rice yield and yield components?
  5. Do the interaction of non-symbiotic bacteria and rice varieties cause significant changes in physical and chemical properties of paddy soil?
  6. Do the interaction of non-symbiotic bacteria and rice varieties cause significant changes in concentration of nutrition elements in grain and rice straw?

Objectives

  1. To study the effect of strains of plant growth promoting bacteria on quantitative rice
  2. To study the effect of strains of plant growth promoting bacteria on some chemical properties
  3. To study the effect of strains of plant growth promoting bacteria on concentration of nutrition elements in grain and rice straw
  4. To study the interaction of strains of plant growth promoting bacteria and rice varieties on rice quantitative characteristics
  5. To study the interaction of strains of plant growth promoting bacteria and rice varieties on some chemical properties of rice plants
  6. To study the interaction of strains of plant growth promoting bacteria and rice varieties on concentration of nutrition elements in grain and rice straw

Materials and methods

In order to investigate the effect of application of different strains of non-symbiotic bacteria on quantitative traits and yield of rice varieties (Hashemi and Gilaneh varieties) and also the physical and chemical properties of paddy soil, a factorial experiment in the form of a randomized complete block design with three replications was conducted since 2019 for two years (including two periods of rice cultivation). Experimental factors include eight levels of inoculation with non-symbiotic bacteria (control, inoculation with the Azotobacter crococum, inoculation with the Pseudomonas fluorescens P169, inoculation with the Azospirillum lipofrom, inoculation with a combination of Azotobacter crococum and Pseudomonas fluorescens, inoculation with a combination of Azotobacter crococum and Azospirillum lipofrom inoculation with a combination of Azospirillum lipofrom and Pseudomonas fluorescens, inoculation with a combination of Azospirillum lipofrom, Azotobacter crococum, Pseudomonas fluorescens) and two varieties of rice, including Hashemi and Gilaneh were considered. Before field preparing, a compound sample of 0-25 cm depth of soil surface was prepared from several points of the experimental field and sent to the soil and water laboratory of the Rice Research Institute to measure the chemical properties of the soil (acidity, organic matter, nitrogen, phosphorus, potassium and zinc). The non-symbiotic bacteria were obtained from the microbial collection of the Soil and Water Research Institute and their population after duplication in Nutrient Broth medium was set at about 108 cfu (colony forming unit) per milliliter. Experimental treatments were performed before seed sowing in the nursery and by inoculation of rice germinated seeds with bacterial suspension. For this purpose, the rice grains are firstly washed with distilled water and placed in a suitable damp cloth to germinate. Then, according to the amount of rice germinated seeds, a certain amount of bacterial suspension is poured into a suitable cleaning container and shaken for one hour to ensure that the seeds are completely inoculated with rhizobacteria. In order to determine the effectiveness of biological fertilizers on the quantitative traits of rice varieties, no chemical fertilizers were used in the experimental plots. Also, to study and compare the growth characteristics and yield of rice varieties in conditions without consumption and with consumption of chemical fertilizers, a control treatment of chemical fertilizers consumption for each rice variety (based on soil chemical properties results) was considered in addition to the above treatments in each repetition. In order to prevent the infiltration of water from plot to another plot, as well as the growth of weeds, the borders are covered with plastic. Rice seedlings was transplanted with 20× 20 cm cultivation pattern. During the rice cultivation period, Trichogramma bee trichocartes was used to control rice stem borer worms, and mechanical weeding was used to control weeds. After each rice cultivation period, soil samples from experimental plots were prepared from a depth of 0-25 cm above the soil surface to measure soil chemical properties (acidity, organic carbon, nitrogen, phosphorus, potassium and zinc). Agronomic traits such as plant height, number of tillers per plant, number of fertile tillers per plant, number of panicles per square meter, panicle length, total number of grain per panicle, filled grain number, grain yield, biological yield, harvest index and nutrient elements concentration (N, P, K) in grain and straw would be measured. Data analysis will be performed with SAS software (version 9.4) and means comparison will be done using LSD5%.