Soil inoculants are bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 or fungi that are added to soils in order to improve plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

 growth by either:

• Freeing up soil nutrients for plant use.
• Entering into symbiotic relationships with plant root systems.
• Acting as antagonistic
  Receptor antagonist
  A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...
  
   organism
  Organism
  In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
  
  s against plant pathogens.

The most commonly used soil inoculants are rhizobacteria

Rhizobacteria

Rhizobacteria are root-colonizing bacteria that form symbiotic relationships with many plants. The name comes from the Greek rhiza, meaning root. Though parasitic varieties of rhizobacteria exist, the term usually refers to bacteria that form a relationship beneficial for both parties...

 that live symbiotically with legumes such as peas

PEAS

P.E.A.S. is an acronym in artificial intelligence that stands for Performance, Environment, Actuators, Sensors.-Performance:Performance is a function that measures the quality of the actions the agent did....

, beans, etc. These bacteria live within specialized nodules on the root systems of legumes, where they process atmospheric nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 into a form available for the plants to use.

Another group of common soil inoculants are mycorrhizal fungi, which attach to the roots of many plant species and help conduct water and nutrients for the plants to use.

List of Soil Inoculant Bacteria

• Acidovorax facilis
  Acidovorax facilis
  Acidovorax facilis is an aerobic, chemoorganotrophic bacterium used as a soil inoculant in agriculture and horticulture.-Morphological and biochemical attributes:...
  
  
• Bacillus subtilis
  Bacillus subtilis
  Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...
  
  
• Rhodococcus rhodochrous
• Bacillus chitinoporus
• Bacillus laterosporus