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Effect of symbiotic and non-symbiotic bacteria strains on clover and rice
(var Hashemi) yield in rice-based cropping system

 

Introduction

Rice (Oryza sativa L.) is the most important crop in the world after wheat, which feed for about two-thirds of the world's population. With the increasing need for food and the restriction of agricultural land, the optimal use of fertile farmland is unavoidable. One of the ways to increase agricultural production is using multi-cropping systems in the year instead of single-cropping system. One of the most important needs in using dual or multi-cropping systems is to preserve water and soil resources from the pollution caused by excessive intake of chemical inputs as well as maintaining and improving soil fertility in the long term. One of the prominent features of the legume family is the ability to establish a symbiotic relationship with rhizobacteria. Clover is one of the plants that is compatible with temperate and humid climates that rice can grow. The use of nitrogen fixation phenomenon has been emphasized as one of the vital necessities for the realization of sustainable agricultural systems. What nowadays encourages developed countries to produce and consume biological fertilizers is their serious attention to environmental impacts caused by the excessive and unbalanced use of chemical fertilizers. One of the most important of these solutions is the use of biological nitrogen fixation technology through inoculation with plant growth promoting bacteria. The use of biological fixation of nitrogen has been emphasized as one of the vital requirements for the implementation of sustainable agricultural systems. Different bacterial genera are vital components of soils. They are involved in various biotic activities of the soil ecosystem to make it dynamic for nutrient turn over and sustainable for crop production. They stimulate plant growth through mobilizing nutrients in soils, producing numerous plant growth regulators, protecting plants from phytopathogens by controlling or inhibiting them, improving soil structure and bioremediating the polluted soils by sequestering toxic heavy metal species and degrading xenobiotic compounds (like pesticides). According to the stated contents, it is necessary to conducting a research to provide advisable and environmentally friendly solutions with the aim of accelerating vegetative growth and yield of clover and ultimately increasing the rice yield.

 

Challenges and necessity

Over the past few decades, the excessive use of chemical inputs on cultivated land for crop production in proportion to the growing population of the planet has led to a variety of environmental crises, water and soil pollution, and a decrease in the quality of agricultural products and unpleasant complications in human health. Winter planting of legumes as a second crop in rotation with rice and the use of plant growth promoting bacteria as a new strategy in plant nutrition management can be considered as a suitable way to increase the quantity and quality of production in rice fields. Clover is one of the forage plants of legume family with biological nitrogen-fixing ability that can be developed in susceptible areas, while producing various benefits to farmers, increases the income level of farmers and reduces the many problems of supplying forage for animal husbandry. On the other hand, with increasing the level of awareness and attention of people to the health of crops, nutrient supply and fertility improvement of plant rhizosphere, especially of rice plant, there needs to be a serious overhaul. Establishing correct agronomic rotation and application of growth promoting bacteria has a significant role in increasing plant yield and can be considered as an effective roadmap for achieving of organic agriculture.

 

Research hypotheses

  1. Does the inoculation with symbiotic bacteria strains significantly change clover forage yield, chemical characteristics and nitrogen levels of the soil?
  2. Does inoculation with non-symbiotic bacteria strains cause a significant change in clover forage yield, chemical characteristics and nitrogen levels of the soil?
  3. Does the inoculation with symbiotic bacteria strains significantly change yield and yield components of rice?
  4. Does inoculation with non-symbiotic bacteria strains cause a significant change in yield and yield components of rice?
  5. Do the interactions of treatments (inoculation with symbiotic and non-symbiotic bacteria) significantly change clover forage yield and chemical characteristics and nitrogen levels of paddy soils?
  6. Do the interactions of treatments (inoculation with symbiotic and non-symbiotic bacteria) cause significant changes in yield and yield components of rice?

 

Objectives

  1. To investigate effect of symbiotic and non-symbiotic bacteria strains on clover yield and chemical characteristics of paddy soils.
  2. To investigate effect of symbiotic and non-symbiotic bacteria strains on yield and yield components of rice.
  3. To assess the interaction between symbiotic and non-symbiotic bacteria strains on clover yield and chemical characteristics of paddy soils.
  4. To assess the interaction between symbiotic and non-symbiotic bacteria strains on yield and yield components of rice.

 

Materials and methods

A factorial experiment was conducted in a randomized complete block design with three replications in Rice Research Institute of Iran, Rasht, during 2016-18, with the aim of selecting and introducing the best strain for increasing the traits of clover plants and rice production, as well as improvement physical and chemical properties of soil. Experimental factors included four inoculation levels with Rhizobium leguminosarum bv.trifolii and four inoculation levels with non-symbiotic plant growth promoting rhizobacteria including: control, Pseudomonas fluorescence, Azotobacter Chroococcum and combined treatment of these bacteria.

 

Final report

The results showed that the effect of nitrogen fixation bacteria on clover forage yield was significant at the p ˂ 0.01 level. The strains 3+ 13 symbiotic bacteria treatment significantly increased forage yield (4456 kg/ha) of clover compared to the control treatment. The effect of non-symbiotic bacteria on soil phosphorus and rice paddy yeild in rice cultivation was significant at the p ˂ 0.05 and p ˂ 0.01 levels respectively, so that the Pseudomonas treatment and the Azotobacter+ Pseudomonas treatment increased soil phosphorus levels by 1.41 and 0.83 mg/ kg respectively, compared to the control treatment. The treatment of Azotobacter+ Pseudomonas had the highest yield (3336 kg/ha) compared to the other treatments. Also, the second year of the experiment had higher organic carbon percentage (1.79), soil nitrogen percentage (0.216) and rice yield (3250 kg/ ha). The results showed that the use of growth promoting bacteria in addition to increasing plant yield by improving soil chemical properties could increase the yield of rice in the next crop and reduce the adverse effects of using chemical fertilizers by moderating the use of these inputs.