Oklahoma State University

Contact Info

Josh Lofton, Assistant Professor
Cropping Systems Specialist
Oklahoma State University
376 AG Hall
Stillwater, OK 74078
Phone: 405-744-3389
FAX Number: 405-744-0354

josh.lofton@okstate.edu

 

 

 

 

Page Title

Soybean Seed Innoculation

 

 

Production Technology - PT98-19, May 1998
Oklahoma Cooperative Extension Service
Ron Sholar, Extension Crops Specialist and Lewis Edwards, Professor of Agronomy

Soybean seed planted on new land or land that has not been in soybean production for several years should be inoculated at planting with a soybean strain of nitrogen-fixing bacteria, Rhizobium japonicum. Soybeans inoculated with the proper strain of bacteria will produce up to half of their own nitrogen.

Nitrogen fixation is the result of a symbiotic (beneficial to both organisms) relationship of rhizobia bacteria and plants. Rhizobia are unicellular, microscopic plants. They invade the soybean plant through root hairs and once established, they take gaseous nitrogen from the atmosphere and convert it to forms used by the soybean plant. In turn, the soybean plants form special structures called "nodules" and rhizobia colonies are enclosed in the nodules. In the symbiotic relationship, the legume plant provides carbohydrates (sugars) and nutrients to the rhizobia for energy and the rhizobia provides nitrogen to the plant.

Legumes in the cowpea "cross inoculation" group (peanuts, cowpeas etc.) can be infected with bacteria that is native in Oklahoma soils. The rhizobia species that inoculates soybeans is not native to Oklahoma soils and must be applied to either the seed or the soil.

 

Nodules on Inoculated Plant

It is critical that soybeans going into new fields be inoculated. Where this is not done, the soybean crop will use available soil nitrogen which will usually be deficient for the crop. These fields are characterized by light green leaves, unthrifty plant growth, and lack of nodules on the plant roots. In some cases, crop failures are observed. Many producers inoculate soybean seed for all fields to be planted each year due to low cost of inoculant. This ensures an abundant supply of the proper bacteria in the soil. 

Inoculant can be either seed or soil-applied. Seed-applied inoculant should be mixed with water, forming a slurry which is used to coat the seed. This should be done several hours before planting to allow the seed to dry. Inoculant can also be applied directly to the hopper box but this is usually less acceptable than wetting/drying of the seed. Do not mix inoculant, seed, and water in the hopper box.

Recently, manufacturers have developed inoculant that is marketed in a liquid slurry. This product can be used either seed or soil-applied. Soil-applied inoculants are applied in the seed furrow at planting with insecticide boxes on the planter. A soil-applied inoculant is easy to apply and provides more bacteria per acre than a seed-applied inoculant; however, it is more expensive to use on a per acre basis. Soil-applied inoculants may be particularly valuable on "new" soybean land. Pre-inoculated seed have been shown to have little benefit. Normal degradation of the bacteria from time of application to planting occurs.

 

Noninoculated Plants

 

Precautions:

  • It is critical that soybeans going into new fields be inoculated. 

    Inoculant Storage and Handling - Soybean bacteria is a living organism and must be handled with care. Handle and store inoculants according to manufacturer's instructions. Don't leave in high temperatures or direct sunlight. The dash of a pickup truck is a poor place to store inoculant.

  • Compatibility with Fungicides - Thiram is the only fungicide that has no adverse effect on rhizobia. All other fungicides reduce rhizobia survival and number of nodules. 

Don't use a seed-applied inoculant with other seed-applied fungicides. Even where Thiram is used, Thiram-treated seed should be planted immediately after treatment. If a seed treatment other than Thiram is used, use a soil-applied inoculant. 

 

No inoculated Four-row Strip Through Field

Bacteria Response to Low pH and Molybdenum - Soybean bacteria is a living organism and will not survive in acid soils and low yields usually result on fields with low pH. Fields with a pH below 5.8 should be limed to provide a favorable environment for the bacteria. Molybdenum is important for the nitrogen fixation process and molybdenum deficiencies can occur at a pH below 6.0. At low pH, an inoculant used in conjunction with molybdenum can be used to avoid a molybdenum deficiency. However, the best solution for low pH and low molybdenum is still to lime the field.  

 

 

Oklahoma State University, in compliance with Title VI and Vii of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, sex, age, religion, disability or status as a veteran in any of its policies, practices or procedures. This includes but is not limited to admissions, employment, financial aid, and educational services.

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1913, in cooperation with the US Department of Agriculture, Sam E. Curl, Director of Oklahoma Cooperative Extension Service, Oklahoma State University, Stillwater, Oklahoma. This publication is printed and issued by Oklahoma State University as authorized by the Dean of the Division of Agricultural Sciences and Natural Resources.

 

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