- PRODUCTION -
Soybean Inoculant –
|By Dr. Ron Levy|
Soybeans are big users of nitrogen, removing about four pounds of nitrogen per bushel. Soybeans that are poorly nodulated will have to take up most of the nitrogen they need from the soil.
Since nitrogen fertilizer is generally not applied to soybeans, a crop that is poorly nodulated will quickly use up the available nitrogen in the soil and become chlorotic from nitrogen deficiency.
Soybean inoculant contains Bradyrhizobium japonicum bacteria. The Bradyrhizobium bacteria forms nodules on soybean roots, and these nodules fix nitrogen from the atmosphere and supply it to the plants. For nitrogen fixation to occur, the nitrogen-fixing bacteria need to be readily available in the soil or must be applied to the seed or soil. When the seed germinates, the bacteria invade the root hairs of the seedling and begin to multiply, forming nodules on soybean roots.
Nodules, which house the bacteria, can be seen shortly after emergence, but active nitrogen fixation does not begin until about the V2 stage. After this, the number of nodules formed and the amount of nitrogen fixed increase with time until about R5.5 (midway between R5 and R6) when they decrease sharply.
Consider field history
If soybeans have been grown on the field in previous years, there may be enough Bradyrhizobium bacteria in the soil to nodulate the soybeans adequately. In that case, an inoculant may not benefit the crop. But if there is not enough Bradyrhizo-bium in the soil, the inoculant may increase yields by two bushels per acre or more on fields that have had soybeans in the recent past.
On fields where soybeans have never been grown, the inoculant has been shown to increase yields by 10 bushels per acre or more.
Poor or failed inoculation
Most fungicide seed treatments should not harm the inoculant if applied according to directions, but be sure to check the label of the specific fungicide seed treatment to be used.
If you have questions concerning inoculation, contact your county Extension service agent.
Dr. Ron Levy is the state soybean specialist with the LSU AgCenter. Contact him at (318) 427-4424 or firstname.lastname@example.org.
When Should Soybeans Be Innoculated?
Inoculation should be considered as follows: